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Dissertations / Theses on the topic 'Semiconductors II-VI'

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Published: 8 July 2022

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1

Claybourn, M. "Transient spectroscopy of II-VI semiconductors." Thesis, Durham University, 1985. http://etheses.dur.ac.uk/9298/.

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DLTS, ODLTS and DLOS have been used to characterise the main deep level trapping centres in some II-VI semiconductors; these were single crystal CdS, (ZnCd)S, CdSe, CdTe and ZnS, and polycrystalline CdS films. Undoped, single crystal CdS contained four electron traps as detected by DLTS, at 0.29eV, 0.41eV, 0.61eV and 0.74eV below the conduction band (CB). The first two were observed in all samples and were due to native defects. The two states of highest energy were found only in material that had been annealed in S or Cd vapours. The 0.61ev level could be photoinduced by illumination at photon energies greater than about 1eV. It decayed in the dark with an activation energy of 0.25eV. The 0.61eV and 0.74eV centres were associated with electrically active extended defects (subgrain boundaries Such samples had dislocation densities of about 10(^10) cm(^-2). Copper was found to be a residual impurity in CdS. It produced two deep hole traps resulting from a crystal field splitting of the Cu d(^9) state. They were detected by ODLTS and DLOS and were found at 0.35eV and 1.lev above the valence band (VB).Introduction of the isoelectronic impurity tellurium into CdS induced a hole repulsive centre at 0.21eV above the VB. This is thought to be an inportant radiative recombination centre. The main electron trap in CdS at 0.41eV was found to shift to higher energy with incorporation of Zn. Replacement of 20% of the Cd with Zn shifted the energy to 0.63eV. The level appeared fixed to the VB and had a similar functional dependence on composition as the band gap. The activation energies of the copper centres observed in CdS remained unchanged with incorporation of Zn up to the composition (^Zn)0.45 (^cd)0.55(^s) showed that the crystal field splitting was constant and that these levels were also pinned to the VB. During the fabrication process of the (ZnCd)S/Cu(_2)S solar cell, a deep level was induced at about 1.2eV below the CB. This is thought to be a recombination centre and one of the contributory factors to the reduction observed in the current collection efficiency of these devices. Polycrystalline CdS films were prepared by silk screen printing (SP) and evaporation. The SP films were annealed at various times and temperatures to improve the crystallinity of the layers. At 640C for 1hr, deep states at 0.16eV and 0.48eV were detected. The levels disappeared when annealed at 670C-700C and a new level was observed at 0.13eV. CdS/Cu(_2)S heterojunctions were prepared on the material sintered at 670C; this induced a further trapping level at 1.1eV and one that was poorly resolved. Copper diffused into the CdS during the fabrication of the device so the states associated with copper were detected at 0.35eV and 1.1eV, The evaporated CdS layers showed that the defect signature was sensitive to the type of substrate. Using Ag instead of the usual SnO(_x), deep states were induced at 0.48eV and 0.98eV below the CB. These Ag-associated impurity centres prevent the indiffusion of Cu during the optimising heat treatment of the CdS/Cu(_2)S heterojunction. This maintains the stoichicmetry of the Cu(_2)S layer, thereby, preventing degradation of the devices. CdSe and copper doped CdSe were found to contain several important defect centres: a native sensitising centre (0.64eV from the VB), a class I recombination centre (0.9eV from the CB), a copper impurity centre (0.2eV from the CB) and two native defects (0.16eVand 0.45eV from the CB). n-type CdTe grown by the Piper-Polich technique contained6 electron traps at 0.15eV, 0.21eV, 0.40eV, 0.47eV, 0.53eV and 0.63eV. Their presence was shown to be dependent upon the method of growth of the crystal by comparing with material grown by other techniques. One or more of these states were thought to be due to extended defects or Te precipitates. Low resistivity ZnS contained two deep electron traps at 0.25eV and O.50eV as detected by DLTS. In addition DLOS showed the presence of four further states at 1.25eV, 1.37eV, 1.89eV and 2.19eV below the CB. The first two are thought to be the strong luminescence centres observed by other workers.
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2

Boyce, Paul John. "Raman spectroscopy of II-VI semiconductors." Thesis, University of East Anglia, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357210.

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3

Wasenczuk, Adam. "Defects in epitaxial II-VI semiconductors." Thesis, University of Southampton, 1998. https://eprints.soton.ac.uk/426603/.

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4

Milnes, James. "The piezoelectric effect in II-VI semiconductors." Thesis, Heriot-Watt University, 1999. http://hdl.handle.net/10399/617.

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5

Luo, Ming. "Transition-metal ions in II-VI semiconductors ZnSe and ZnTe /." Morgantown, W. Va. : [West Virginia University Libraries], 2006. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=4630.

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Thesis (Ph. D.)--West Virginia University, 2006.<br>Title from document title page. Document formatted into pages; contains xiv, 141 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 135-141).
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6

Meredith, Wyn. "II-VI blue emitting lasers and VCSELs." Thesis, Heriot-Watt University, 1997. http://hdl.handle.net/10399/695.

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7

Cairns, John William. "The interfaces of II-VI/III-V semiconductors." Thesis, Cardiff University, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.296381.

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8

Gabriel, Tim. "The electrodeposition of mesoporous type II-VI semiconductors." Thesis, University of Southampton, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.438733.

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9

Stevens, Christopher John. "Time-resolved spectroscopy of excitons in II-VI heterostructures." Thesis, University of Oxford, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.308909.

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10

McNamee, Michael Jonathan. "Optical studies of electronic excitations in II-VI semiconductors." Thesis, University of Oxford, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359471.

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11

Urbaszek, Bernhard. "Fundamental studies of excitonic properties in II-VI semiconductors." Thesis, Heriot-Watt University, 2001. http://hdl.handle.net/10399/540.

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12

Walker, Nicholas J. "Nonlinear elastic and electrical behaviour in some (II-VI) and (IV-VI) semiconductors." Thesis, University of Bath, 1986. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.373402.

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13

Cheng, Hung Hsiang. "Magneto-optical studies of II-VI and III-V heterostructures." Thesis, University of Oxford, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318838.

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14

Moreira, Wendel Lopes. "Síntese e estabilização de pontos quânticos coloidais de semicondutores II-VI e IV-VI." [s.n.], 2005. http://repositorio.unicamp.br/jspui/handle/REPOSIP/277440.

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Orientador: Carlos Lenz Cesar<br>Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica<br>Made available in DSpace on 2018-08-04T09:35:25Z (GMT). No. of bitstreams: 1 Moreira_WendelLopes_M.pdf: 8515504 bytes, checksum: e80c0c01881efcfade7d7e39b55ade9a (MD5) Previous issue date: 2005<br>Resumo: Não informado<br>Abstract: Not informed.<br>Mestrado<br>Física da Matéria Condensada<br>Mestre em Física
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15

Romano, Ricardo. "Nanocompositos e nanoestruturas de semicondutores das familias II-VI e IV-VI." [s.n.], 2007. http://repositorio.unicamp.br/jspui/handle/REPOSIP/249039.

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Orientador: Oswaldo Luiz Alves<br>Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Quimica<br>Made available in DSpace on 2018-08-08T20:29:31Z (GMT). No. of bitstreams: 1 Romano_Ricardo_D.pdf: 7756171 bytes, checksum: bd3a8af5af06fb7ec50b3cd881d41bfd (MD5) Previous issue date: 2007<br>Resumo: O desenvolvimento das nanoestruturas e suas aplicações compõem uma das áreas científicas em mais dinâmica ascensão. Grande parte dos estudos na área concentra-se nos métodos de preparação e, de uma forma geral, podem ser divididos em métodos físicos ou químicos. Os primeiros reúnem processos baseados em sistemas de feixes moleculares ou litografia, enquanto os últimos envolvem reações químicas em meios onde o crescimento dos cristais possa ser controlado e estabilizado. Nesta Tese foram preparadas nano(micro)estruturas de semicondutores II-VI e IV-VI a partir de três abordagens químicas distintas. Na primeira, foram obtidos nanocompósitos pelo encapsulamento de nanocristais de CdS e PbS no ambiente microporoso de um vidro transparente, comercialmente conhecido por Vycor®. A técnica envolvida foi a impregnação de peças do vidro com precursor single-source seguida por tratamento térmico visando a pirólise in situ do precursor. Efeitos de confinamento quântico no espectro óptico e micrografias eletrônicas de transmissão confirmaram a natureza nanométrica da fase ocluída. Na segunda, foram obtidos cristais nano e micrométricos de CdS, PbS e ZnS através da técnica conhecida por moldagem molecular por solvente coordenante, na qual precursores single-source foram tratados solvotermicamente em solventes coordenantes e levaram à formação de bastões de CdS, microestrelas de PbS e intercalatos de ZnS com etilenodiamina. Na última abordagem, nanocristais coloidais de CdSe com diferentes faixas de tamanho (2 a 7 nm) foram preparados com a finalidade de se estudar o comportamento da estrutura local e dinâmica vibracional do CdSe em função da redução no tamanho e substituição do agente de recobrimento usado na síntese<br>Abstract: The development of nanostructures and their applications constitute one of the most exciting scientific areas. A great number of studies in this area concern the preparation methods. Generally, they are classified in physical and chemical methods. The former class is based on molecular beam and lithography techniques, while the latter involves chemical reactions where crystal growth can be controlled and stabilized. In this Thesis, II-VI and IV-VI semiconductor nano(micro)structures were prepared according to three different approaches. In the first one, nanocomposites were obtained through the encapsulation of CdS and PbS nanocrystals into a porous and transparent commercial glass, named Vycor®. Glass pieces were impregnated with single-source precursors and, then, thermally treated in order to achieve in situ pyrolysis, making use of the porous environment as the stabilizer for the crystal growth. Quantum confinement effects in the optical spectrum and transmission electron micrographs characterized the nanometric dimensions of the occluded phase. In the second approach, a technique known as molecular templating by coordenant solvents was employed in order to obtaining CdS, PbS and ZnS nano(micro)crystals showing unusual morphologies. Single-source precursors were solvothermically treated in such solvents leading to CdS nanowires, PbS microstars and ZnS-ethylenediamine intercalates. In the last approach, colloidal CdSe nanocrystals with different size ranges (2 up to 7 nm) were prepared and employed in the study of the local structure and vibrational dynamics of CdSe as a function of crystal size reduction and substitution of the covering agent used in the synthetic procedure<br>Doutorado<br>Quimica Inorganica<br>Doutor em Ciências
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16

Tran, Tuyen K. "Optical properties of II-VI semiconductor materials and superlattice structures." Diss., Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/30929.

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17

Cornet, i. Calveras Albert. "Estudio por medio de espectroscopia picosegundo de los compuestos II-VI sometidos a fuerte excitación óptica." Doctoral thesis, Universitat de Barcelona, 1987. http://hdl.handle.net/10803/665808.

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En la pasada década, se han observado nuevas bandas de luminescencia en los semiconductores cuando son excitados fuertemente por medio de láseres (fotoexcitacion). La interpretación del origen de estas bandas era variado y ha sido objeto de controversias y discusiones entre los diferentes autores. Finalmente, por medio de experiencias complementarias (efecto Raman, scattering con luz I.R., espectroscopia de excitación, fotoconducción)) se ha probado que en CuCl tiene lugar la formación de moleculas biexcitónicas y que en Ge y en Si, las altas excitaciones producen un plasma electrón-hueco. Sin embargo, en los compuestos II-VI, la interpretación es más difícil, y si bien en alguno de ellos (ZnO) ha quedado bien establecida la existencia de procesos de colisión inelásticos, en general, hay controversias acerca de la interpretación de las llamadas bandas M y P. Generalmente, una de las características comunes de todos los experimentos citados es el uso de láseres nanosegundo para el estudio, por medio de la espectroscopia integrada en el tiempo (técnicas de luminescencia o de ganancia-absorción), de las propiedades de dichos materiales sometidos a excitaciones fuertes. Estas condiciones experimentales dan lugar a ciertas dificultades, que se resuelven con el empleo de técnicas picosegundo, ya que en efecto, el uso de un láser psicosegundo de alta potencia (láser YAG), permite la excitación homogénea de la muestra en la dirección de la excitación, por medio de la absorción a dos fotones. Además, dado que la duración de la impulsión es menor oue el tiempo de vida de las diferentes excitaciones elementales (excitón, biexcitón, plasma electron-hueco...) podemos obtener una dinámica de la relajación de portadores que tiene lugar al final de la impulsión excitadora y, con ello, clarificar algunas de las contradicciones citadas anteriormente. En el dominio de las fuertes excitaciones picosegundo, los experimentadores pueden escoger entre una excitación “caliente” pero relativamente homogénea (excitación a dos fotones) y una excitación “fría” (con un fotón de energía) pero inhomogénea. El primer método nos conduce a .la utilización de láseres de potencia y el segundo, al empleo de láseres de longitud de onda reglable. Nosotros hemos empleado el método de la excitacion caliente. Este método exige tener en cuenta los problemas de termalización del sistema electrón-hueco excitado. Dado que esta cuestión es esencial en este tipo de experiencias, gran parte de esta memoria ha sido consagrada al estudio de dicha termalización. El capítulo I contiene la presentación del conjunto experimental y algunos datos de los materiales estudiados CdSe y CdS. En el capítulo II, calcularemos un modelo simple para prever la cinética de temperatura del plasma. Finalmente, el capitulo III contiene una discusiónsobre la naturaleza de las diferentes líneas de luminescencia del espectro de los semiconductores II-VI estudiados.
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18

Wagner, Franz X. "Excimer laser ablation and processing of II-VI compound semiconductors." Thesis, University of Hull, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.363271.

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19

Blewett, Ian James. "Ultrafast nonlinear optical processes in wide-gap II-VI semiconductors." Thesis, Heriot-Watt University, 1996. http://hdl.handle.net/10399/754.

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20

Tookey, Andrew. "Ultrafast four-wave-mixing in wide-bandgap II-VI semiconductors." Thesis, Heriot-Watt University, 1998. http://hdl.handle.net/10399/1261.

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21

O'Donnell, Cormac Brendan. "MBE growth and characterisation of ZnSe-based II-VI semiconductors." Thesis, Heriot-Watt University, 2000. http://hdl.handle.net/10399/524.

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22

Horsfall, Alton Barrett. "Electrical and magnetic properties of II-VI diluted magnetic semiconductors." Thesis, Durham University, 1997. http://etheses.dur.ac.uk/4984/.

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The electrical and magnetic properties of MOVPE grown epitaxial layers of Hg(_1-x)Mn(_x)Te layers has been investigated using a number of techniques. The samples have been grown by the Inter Diffused Multilayer Process, (IMP) on (100) semi insulating GaAs substrates with ZnTe and CdTe buffer layers. The samples have been shown to show a number of phenomena nopt observed in the bulk material, such as an anomaly in the resistivity, rnagnetoresistance related to the intrinsic magnetism of the material, and saturation of the room temperature magnetisation. In general the samples are of a highly compensated nature with the value of |R(_H)e|(^-1) varying between l0(^14) and 5xI0(^17) cm(^-3) at 20K, the Hall mobilities varying between 8 and 3.5x10(^5) cm(^2)V(^-1)s(^-1) at 20K. Magnetically, the samples generally show a paramagnetic signal that is swamped by the diamagnetic background of the substrate and buffer layers. The paramagnetisrn can be well modelled using a Curie Weiss fit. A number of the samples show a saturation in the magnetisation, which, has been explained via the use of vacancy ordering within MnTe regions in the sample. The susceptibility of the samples has been investigated using a Faraday balance system, and this data has been fitted using; a cluster model for Mn ions within the sample. The photomagnetisation of Cd(_0.9)Mn(_0.1)Te:In has been investigated using a faraday balance system, and modelled using the work of Dietl and Sample, to calculate the number of polarons that had formed on donors in the sample, ΔN(_D)(^MAG) = 1.28x10(^15)cm(^-3). The number of donors in the sample has been measured by means of the Hall effect, ΔN(_D)(^ELEC) = 1.92x10(^15)cm(^-3), and this value compared to that obtained from the model. We have proposed a model to explain this discrepancy based on the concept of band tails in the impurity band.
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23

Spellward, Paul. "Analytical electron diffraction from III-V and II-VI semiconductors." Thesis, University of Bristol, 1990. http://hdl.handle.net/1983/bf55826f-4baf-4e0c-abe8-de539218626e.

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This thesis describes the development and evaluation of a number of new TEM-based techniques for the measurement of composition in ternary III-V and II-VI semiconductors. New methods of polarity determination in binary and ternary compounds are also presented. The theory of high energy electron diffraction is outlined, with particular emphasis on zone axis diffraction from well-defined strings. An account of TEM microstructural studies of CdHg1-, Te and CdTe epitaxial layers, which provided the impetus for developing the diffraction-based analytical techniques, is given. The wide range of TEM-based compositional determination techniques is described. The use of HOLZ deficiency lines to infer composition from a lattice parameter measurement is evaluated. In the case of CdxHg1. XTe, it is found to be inferior to other techniques developed. Studies of dynamical aspects of HOLZ diffraction can yield information about the dispersion surface from which a measure of composition may be obtained. This technique is evaluated for AIXGal_XAs, in which it is found to be of some use, and for CdXHg1. Te, in which the large Debye-Waller factor associated with mercury is discovered to render the method of little value. A number of critical voltages may be measured in medium voltage TEMs. The [111] zone axis critical voltage of CdxHgl_XTe is found to vary significantly with x and forms the basis of an accurate technique for composition measurement in that ternary compound. Other critical voltage phenomena are investigated. In AIXGa 1-,B As and other light ternaries, a non-systematic critical voltage is found to vary with x, providing a good indicator of composition. Critical voltage measurements may be made by conventional CBED or by various other techniques, which may also simultaneously yield information on the spatial variation of composition. The use of diffraction contrast imaging, large angle CBED and convergent beam imaging is evaluated and shown to have some advantages for flat samples. In studies of growth mechanisms, microstructures and even macroscopic properties, knowledge of the polarity of a zincblende structure crystal may be valuable. Methods of polarity determination are surveyed. Two new TEM-based techniques are described and results from a range of II-VI and III-V semiconductors are presented
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24

Lancaster, Adam. "Mid-IR waveguide lasers in transition metal doped II-VI semiconductors." Thesis, Heriot-Watt University, 2017. http://hdl.handle.net/10399/3342.

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This thesis focuses on the development of compact Mid-IR waveguide laser systems in transition metal doped II-VI semiconductors. These waveguide lasers have been developed to produce high brightness and compact sources in the Mid-IR. The wavelength tuneable operation of Cr:ZnSe waveguides was investigated. The waveguides were fabricated using ultrafast laser inscription. The waveguide laser demonstrated a tuning range of 2080 - 2883 nm, with more than 15 mW of output power across the full range. This resulted in a tuneable bandwidth of 39 THz, which is the widest range demonstrated by a Mid-IR waveguide laser. Modelocking of a Cr:ZnSe waveguide laser was investigated using a SESAM. This resulted in the demonstration of a CW modelocked laser with a PRF of 308 MHz, pulse energy of 0.3 nJ and a pulse width of 638 fs. In addition, a CW modelocked laser was demonstrated with a PRF of 1.03 GHz, this is the fastest PRF of any Cr:ZnSe laser demonstrated. Other transition metal doped II-VI semiconductors were investigated. Waveguides were developed in Cr:ZnS because of its improved thermal properties compared with Cr:ZnSe for future power scaling applications. The Cr:ZnS waveguide laser emitted 97 mW at a central wavelength of 2333 nm. Waveguide laser operation was investigated in Fe:ZnSe for laser operation in the 3.7 to 5 μm spectral band. Firstly, low-loss laser waveguide parameters were investigated in Fe:ZnSe. The passive characterisation found the waveguide propagation losses to be as low as 0.4 dB/cm, which is much lower than those demonstrated in other ULI cladding waveguides in Cr:ZnSe and Cr:ZnS. The low-loss waveguides were inserted inside a cryostat for CW laser operation. A free running CW laser operation with an Fe:ZnSe waveguide laser was demonstrated. An output power of 76 mW was produced at 4122 nm with a pump power of 908 mW. This work highlights the operational wavelength versatility of ULI fabricated depressed cladding waveguides.
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25

Parker, David. "Structure and photoelectrochemistry of nanostructured II-VI semiconductors for photovoltaic applications." Thesis, University of Bristol, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.681734.

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ZnO nanorods, sensitised to visible light using dyes, quantum dots, or thin films of low-bandgap semiconductors are commonly used as photoanodes in novel solar cells . They have a number of exciting properties for such an application. These include a direct conducting path for electrons, with few grain boundaries, and an increased surface area offering enhanced optical absorption. They are also able to sustain a depletion layer, the electric field this creates can effectively separate charge carriers at the nanorod/sensitiser interface, reducing recombination. However, despite these potential benefits, devices made using 1-D ZnO nanostructures are so far unable to match the performance of devices constructed using mesoporous Ti02 films. One of the reasons given for this is the presence of mid-bandgap states at the surface, which are investigated in this work. ZnO nanorods were grown using a hydrothermal growth technique. Using cyclic voltammetry and photocurrent measurements, mid-band gap trap states were identified and their position found to be centred around 0.8V below the conduction band. Visible luminescence from defect states identified by photoluminescence may be associated with these states. The effects of annealing in air at 180°C, 350°C and 450°C were investigated, all three experimental techniques showed that annealing at temperatures equal to or greater than 350°C was effective in reducing the density of these states. Annealing was also found to have a critical effect on doping density of the nanorods, with implications for both conductivity and the characteristics of the depletion layer that forms at the interface of the nanorods. The doping density was measured using a modified form of MottSchottky analysis and found to be high (> 1020cm-3) for as-grown rods, and only slightly reduced by annealing at temperatures up to 350°C. Annealing at 450°C however reduced the doping density by over two orders of magnitude. These results are consistent with previously reported evidence that incorporated hydrogen acts as a donor for ZnO. A study of the structure of alloyed CdSel-xTex quantum dots was also carried out using a combination of high resolution transmission electron microscopy, selected area electron diffraction and X-ray diffraction. This showed that both wurtzite and zinc blende QDs were present at all compositions, with no clear phase transition between different compositions. CdSe QDs were then successfully used to sensitise annealed nanorods to visible light. Electron transport within the rods was shown to be efficient. The results in this work should prove useful in understanding how best to utilise 1D ZnO nanostructures in solar cells, and provide insights into the nature of defect states which have so far limited the efficiency of such devices.
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26

Railson, Stuart Vaughan. "Optical spectroscopy of Cd←1←←←xMn←xTe heterostructures." Thesis, University of East Anglia, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318019.

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27

Alshawa, Amer K. "Luminescence properties of rare earth doped III-V and II-VI semiconductors." Ohio : Ohio University, 2000. http://www.ohiolink.edu/etd/view.cgi?ohiou1179167587.

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28

Adams, Richard Andrew. "Time resolved photoluminescence studies of the lasing mechanisms in II-VI semiconductors." Thesis, University of Oxford, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.360020.

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29

Rueda-Fonseca, Pamela. "Magnetic quantum dots in II-VI semiconductor nanowires." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GRENY015/document.

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Dans ce travail de thèse a été développé et étudié un nouveau type d'objet semiconducteur magnétique : des boîtes quantiques de CdMnTe insérées dans des nanofils de ZnTe/ZnMgTe constituant une structure de type cœur-coquille. L'objectif était d'étudier la croissance par épitaxie par jets moléculaires et les propriétés fondamentales de ces hétéro-structures complexes. Dans ce but deux aspects principaux ont été abordés : i) la qualité et le contrôle des propriétés structurales, électroniques et magnétiques de ces objets, grâce à une maîtrise de leur croissance et ii) l'obtention d'informations quantitatives locales sur la composition chimique de ces nanostructures inhomogènes. Pour atteindre ces objectifs, nous avons divisé notre étude en quatre étapes. La première étape de ce travail a été concentrée sur l'étude quantitative de la formation des particules d'or servant de catalyseurs à la croissance des nanofils. La seconde étape a porté sur l'analyse des mécanismes de croissance et des paramètres gouvernant la croissance des fils de ZnTe. En particulier deux types de fils ont été observés : des fils cylindriques de structure wurtzite et des fils coniques de structures zinc-blende. Un modèle de croissance guidée par la diffusion a été utilisé pour rendre compte de certains des résultats quantitatifs présentés dans cette partie. La troisième étape a concerné l'insertion de boîtes quantiques de CdMnTe dans des nanofils de structure cœur-coquille ZnTe/ZnMgTe. Une étude préalable des paramètres pertinents influençant les propriétés magnéto-optiques de ces objets, tels que le confinement de la boîte quantique, l'incorporation du Mn et l'anisotropie de contrainte créée par la structure, a été menée. La quatrième et dernière étape de ce travail a porté sur l'interprétation quantitative de mesures d'analyse dispersive en énergie effectuées sur des nanofils de structure cœur-multicoquille. Un modèle géométrique a été proposé, permettant de retrouver la forme, les dimensions et la composition chimique des boîtes quantiques et des coquilles. Cette étude a été couplée à des mesures de caractérisation telles que la cathodo-luminescence, la micro-photo-luminescence et la spectroscopie magnéto-optique effectuées sur le même nanofil<br>In this PhD work a novel type of magnetic semiconductor object has been developed: Cd(Mn)Te quantum dots embedded in ZnTe/ZnMgTe core-shell nanowires. The goal was to investigate the growth, by molecular beam epitaxy, and the fundamental properties of these complex heterostructures. For that purpose, two main issues were addressed: i) gaining control of the structural, electronic and magnetic properties of these quantum objects by mastering their growth; and ii) obtaining quantitative local knowledge on the chemical composition of those non-homogeneous nanostructures. To tackle these topics, our research was divided into four stages. The first stage was devoted to perform a quantitative study of the formation process of the Au particles that catalyze the growth of nanowires. The second stage involved the analysis of the mechanisms and parameters governing the growth of ZnTe nanowires. In particular, two different types of nanowires were found: cone-shaped nanowires with the zinc-blende crystal structure and cylinder-shaped nanowires with the hexagonal wurtzite structure. A diffusion-driven growth model is employed to fit some of the quantitative results presented in this part. The third stage focused on the insertion of pure CdTe quantum dots containing Mn ions in the core-shell nanowires. An initial study of the relevant parameters influencing the magneto-optical properties of these objects, such as the quantum dot confinement, the Mn incorporation, and the strain anisotropy, was performed. The four and last stage of this work concerned the quantitative interpretation of Energy-Dispersive X-ray spectroscopy measurements performed on single core-multishell nanowires. A geometrical model was proposed to retrieve the shape, the size and the local composition of the quantum dot insertions and of the multiple layers of the heterostructures. This study was coupled to other complementary characterization measurements on the same nanowire, such as cathodo-luminescence, micro-photo-luminescence and magneto-optical spectroscopy
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30

Bensaid, Nacer-Eddine. "Use of phonon echoes in the study of II-VI compounds and dielectric Bi←1←2GeO←2←0:Cr." Thesis, Lancaster University, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293208.

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31

Little, Reginald Bernard. "The synthesis and characterization of some II-VI semiconductor quantum dots, quantum shells and quantum wells." Diss., Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/30573.

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32

Shkurmanov, Alexander, Chris Sturm, Jörg Lenzner, et al. "Selective growth of tilted ZnO nanoneedles and nanowires by PLD of patterned sapphire substrates." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-210898.

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We report the possibility to control the tilting of nanoneedles and nanowires by using structured sapphire substrates. The advantage of the reported strategy is to obtain well oriented growth along a single direction tilted with respect to the surface normal, whereas the growth in other directions is suppressed. In our particular case, the nanostructures are tilted with respect to the surface normal by an angle of 58°. Moreover, we demonstrate that variation of the nanostructures shape from nanoneedles to cylindrical nanowires by using SiO2 layer is observed.
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33

Khallaf, Hani. "Chemical Bath Deposition of Group II-VI Semiconductor Thin Films for Solar Cells Applications." Doctoral diss., University of Central Florida, 2009. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2101.

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Chemical bath deposition (CBD) is the analog in liquid phase of the well-known chemical vapor deposition technique in the vapor phase. In CBD, deposition of thin films takes place from aqueous solutions at low temperatures by a chemical reaction between dissolved precursors, with the help of a complexing agent. Among all techniques used to grow Group II-VI semiconductors, CBD has the advantage of being a simple, low temperature, and inexpensive large-area deposition technique. So far, its contribution in thin film solar cells industry has been mainly limited to growing n-type CdS and/or ZnS window layers for CdTe-based and CIGS-based solar cells. In this work we first optimize the CBD process of CdS using nitrilotriacetic acid and hydrazine as complexing agents as an alternative to ammonia. We then study the effect of the cadmium precursor on the optical/electrical properties, as well as crystal structure, morphology, and composition of CBD-CdS films. A better understanding of the CBD process of CdS as a whole has been achieved and high quality CBD-CdS films have been obtained. Next, we investigate in-situ doping of CBD-CdS with group III elements, such as B, Al, In, and Ga. The objective is to show that CBD is capable of not only growing CdS but also of doping it to reduce its resistivity and, as a result, facilitate its use in solar cells as well as other optoelectronic device fabrication. A four orders of magnitude drop of film resistivity has been achieved without a significant change in film bandgap, structure, or morphology. Finally, we test the possibility of using CBD to grow transparent conducting oxide (TCO) films, such as Al-doped ZnO films and cadmium stannate films. First, we study CBD of ZnO and later in-situ doping of ZnO using Al. High quality ZnO thin films have been grown using CBD with the help of four different complexing agents. Post heat treatment in argon ambient helped reduce resistivity of CBD-ZnO undoped films to ~ 10-1 &#937;-cm. In-situ doping of such films using Al shows promising results. Such films could be an alternative to indium tin oxide (ITO) layers that are commonly used as TCO layers for solar cells. Another approach is to use CBD to grow CdO and SnO2 thin films, with the goal of obtaining Cd2SnO4 by later annealing of these two layers. Cadmium stannate is another TCO candidate that could replace ITO in the near future. We have succeeded in growing CBD-CdO thin films using three different complexing agents. Undoped CBD-CdO films with a resistivity as low as 1.01 x10-2 [omega]-cm and a carrier density as high as 2.59 x 1020 cm-3 have been obtained. SnO2 films have been successfully grown using CBD. Fabrication of Cadmium stannate thin films using CBD is investigated. In summary, our objective to expand the use of CBD beyond just growing CdS and ZnS, and to test the possibility of using it for in-situ doping of group II-VI semiconductors as well as TCO layers fabrication proved to be successful. We believe that this may have a significant impact on solar cells as well as other optoelectronic devices fabrication industry, due to the simplicity and the cost-effectiveness of CBD.<br>Ph.D.<br>Department of Physics<br>Sciences<br>Physics PhD
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34

Laura, M. Robinson. "USING TIME-RESOLVED PHOTOLUMINESCENCE SPECTROSCOPY TO EXAMINE EXCITON DYNAMICS IN II-VI SEMICONDUCTOR NANOSTRUCTURES." University of Cincinnati / OhioLINK, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=ucin980259259.

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35

Kumar, Vishwanath. "Characterization Of Large Area Cadmium Telluride Films And Solar Cells Deposited On Moving Substrates By Close Spaced Sublimation." [Tampa, Fla.] : University of South Florida, 2003. http://purl.fcla.edu/fcla/etd/SFE0000218.

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36

Godde, Tillmann [Verfasser], Ilya [Akademischer Betreuer] Akimov, and Thomas [Gutachter] Weis. "Dynamical properties of excitonic quasi-particles in II-VI semiconductors / Tillmann Godde. Betreuer: Ilya Akimov. Gutachter: Thomas Weis." Dortmund : Universitätsbibliothek Dortmund, 2013. http://d-nb.info/1101476524/34.

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37

Arnoult, Alexandre. "Dopage par modulation d'hétérostructures de semiconducteurs II-VI semimagnétiques en épitaxie par jets moléculaires." Université Joseph Fourier (Grenoble), 1998. http://www.theses.fr/1998GRE10237.

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Une etude theorique preliminaire a cette these a prevu que lorsque l'on introduit un gaz de trous bidimensionnel (2d) dans un puits quantique de semiconducteur semimagnetique, l'interaction entre les spins localises et les porteurs de charges induit une transition de phase ferromagnetique. Nous avons mis au point l'elaboration d'un tel systeme a base de tellurures en epitaxie par jets moleculaires, ainsi que la caracterisation au niveau microscopique des interfaces, du dopage et du transfert de porteurs dans le puits quantique. Ceci nous a permis d'elaborer des echantillons ayant donne lieu a toute une serie d'etudes physiques. Le dopage par modulation d'heterostructures de semiconducteurs ii-vi a base de tellure en epitaxie par jets moleculaires n'avait ete realise jusqu'a notre etude que pour un dopage de type n, sur des structures comportant du cdmgte comme materiau barriere, avec peu de magnesium. Or cet alliage est la clef de la realisation d'un bon confinement quantique dans les tellurures, surtout pour le dopage de type p ou la concentration en mg doit etre augmentee. L'utilisation d'une source d'azote ecr, dopant de type p, et l'optimisation des parametres de la croissance ont permis l'obtention d'un gaz de trous 2d de bonne densite, comme le montrent la spectroscopie optique, l'effet hall et la capacite-tension. L'etude de structures interdiffusees par sims, diffraction de rayon x et spectroscopie optique, nous a de plus permis de mieux comprendre les mecanismes de degradation en cours de croissance de nos couches comportant du magnesium, et dopees a l'azote. Un modele base sur la diffusion de l'azote a ete propose. Il a ensuite ete possible de realiser des structures semimagnetiques dans lesquelles l'interaction entre un gaz de trous 2d et des spins localises de manganese a permis la mise en evidence de la transition de phase ferromagnetique attendue theoriquement. Par ailleurs, un nouveau dopant de type n pour l'epitaxie par jets moleculaire des tellurures a ete teste avec succes sur des couches epaisses, ainsi que pour des heterostructures. Il s'agit de l'aluminium, dont le domaine d'utilisation est plus etendu que les autres dopants utilises jusqu'a present, puisqu'il permet d'obtenir une bonne efficacite meme sur des couches comportant du magnesium.
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Cremel, Thibault. "Vers une source de photons uniques opérationnelle à base de nanofils semiconducteurs." Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAY064/document.

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Le développement récent de la théorie quantique de l’information porte la communauté scientifique à s’intéresser de plus en plus aux sources de photons uniques. En effet, ces sources peuvent par exemple être utilisées pour le calcul quantique optique ou la cryptographie quantique pour améliorer les performances de distribution des clés et éviter les écoutes ou tentatives de hacking. Par conséquent, il est nécessaire de disposer de sources fiables et pour des applications réalistes, le défi est d'obtenir des sources de photons uniques qui fonctionnent jusqu'à température ambiante.Notre groupe à récemment démontré qu'en insérant une boîte quantique de CdSe dans un nanofil de ZnSe, l'émission de photons uniques pouvait être obtenue jusqu'à température ambiante. Néanmoins, ces nanofils avaient un rendement quantique faible et n'étaient pas orientés verticalement à la surface des échantillons du fait de leur croissance suivant l'orientation cristallographique (001). Ces nanofils verticaux ont pour intérêt de pouvoir être aisément couplés à des structures photoniques pour augmenter la collection des photons et leur croissance est favorisée avec des substrats orientés suivant l'orientation cristallographique (111).Dans ce contexte, le but de ce travail de doctorat est de développer la croissance de boîtes quantiques de CdSe insérées dans des nanofils de ZnSe verticaux suivant l'orientation cristallographique (111) par épitaxie par jet moléculaire, d'en étudier les propriétés optiques jusqu'à température ambiante pour des applications potentielles en tant que sources de photons uniques, et de coupler ces nano-objets à des structures photoniques pour augmenter la collection de photons. Pour atteindre ces objectifs, nous avons divisé notre étude en trois points.La première étape de ce travail est concentrée sur le développement de la croissance de nanofils de ZnSe verticalement orientés et passivés par une coquille semiconductrice de ZnMgSe. Nous observons que grâce à cette coquille, l’émission lumineuse de nanofils uniques augmente de plus de deux ordres de grandeur. Dans un second temps, nous démontrons la possibilité d’insérer des boîtes de CdSe dans ces nanofils de ZnSe suivant différentes conditions de croissance. L’influence de ces conditions de croissance est mise en évidence par des études structurales et de composition de ces nano-objets. Des études optiques en fonction de la température montrent que ces nanofils émettent jusqu'à température ambiante. De plus, l'étude du temps de déclin de nanofils uniques révèle que ces fils sont robustes et insensibles aux canaux de recombinaison non-radiatifs jusqu'à 200 K. La troisième étape de ce travail concerne l'augmentation de la collection des photons de ces nano-objets. Nous montrons dans un premier temps qu’en changeant l’environnement diélectrique d’une boîte quantique, son taux d’émission spontanée peut être augmenté. Puis nous montrons la possibilité de créer des fils photoniques à partir des boîtes quantiques insérées dans des nanofils, en recouvrant ces fils d'une épaisse coquille diélectrique. A la lumière d'expériences de microphotoluminescence - qui montrent que ces fils photoniques augmentent efficacement la collection de photons - et de simulations, nous discutons l'intérêt de l'orientation du dipôle (parallèle ou perpendiculaire à l'axe de croissance du nanofil) dans ces structures<br>The recent development of the quantum information theory focuses the interest of the scientific community on single-photon sources. Indeed, these sources can be used for instance for optical quantum computing or quantum cryptography to improve the quantum key distribution performances and avoid eavesdropping. Consequently, it is necessary to have reliable single-photon sources and for realistic applications, the challenge is to get a single-photon source operating up to room temperature.Our group recently demonstrated that by inserting a quantum dot of CdSe in a nanowire of ZnSe, single-photon emission could be obtained up to room temperature. Still, these nanowires had a low quantum yield and were not vertically oriented on the as-grown sample since they were grown along the (001) crystallographic orientation. The interest of vertically oriented nanowires is that they can be coupled to photonic structures to increase their photons collection and their growth is favored on (111)-oriented substrates.In this context, the aim of this PhD work is to develop the growth of vertically oriented ZnSe-CdSe nanowire quantum dots along the (111) crystallographic orientation by molecular beam epitaxy, to study their luminescence up to room temperature for single-photon sources applications, and to couple these nano-objects to photonic structures to increase the photons collection. To reach this goal, we divided this project in three steps.The first step focuses on the development of vertically oriented ZnSe nanowires, passivated with a semiconductor shell of ZnMgSe to enhance their luminescence. In a second step, we demonstrate the possibility to insert CdSe quantum dots in these ZnSe nanowires, using different growth conditions for the quantum dot. The influence of these growth conditions is studied with structural and composition analysis of these nano-objects. Optical studies as a function of the temperature show that these nanowires emit up to room temperature. Moreover, decay-time studies on single nanowire quantum dots reveal that these nanowires are robust and insensitive to non-radiative recombination channels up to 200 K. The third step of this work concerns the enhancement of the light collection from these nano-objects. First, we show that by changing the dielectric environment of the quantum dot, its decay-rate can be increased. Then, we show the possibility to create photonic wires by covering these nanowire quantum dots with a thick dielectric shell. In the light of microphotoluminescence experiments – which show that these photonic wires efficiently increase the photons collection – and simulations, we discuss the interest of the dipole orientation (parallel or perpendicular to the nanowire growth axis) in these structures
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39

Gemain, Frédérique. "Etudes spectroscopiques du dopage dans les matériaux II-VI pour les détecteurs infrarouge et les cellules photovoltaïques." Phd thesis, Université de Grenoble, 2012. http://tel.archives-ouvertes.fr/tel-00849144.

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Ce travail de thèse présente les caractéristiques optiques et électriques de dopants dans des couches de CdHgTe, CdZnTe et CdS. Ces 3 matériaux II-VI ont pour point commun d'être utilisés dans des dispositifs de détection, que ce soit la détection de lumière infrarouge pour les couches de CdHgTe et CdZnTe ou la détection visible comme c'est le cas pour le CdS. La caractérisation optique de ces couches de matériaux II-VI a été réalisée par la technique de photoluminescence et corrélée à des mesures électriques effectuées par effet Hall en température. Dans un premier temps, une étude du dopage intrinsèque par les lacunes de mercure et du dopage extrinsèque par incorporation d'arsenic de l'alliage CdHgTe, couche active des détecteurs IR a été réalisée. Pour cela, des mesures optiques par photoluminescence (sur un banc mis en place au laboratoire pendant la 1ere année de thèse permettant de travailler depuis les basses températures jusqu'à l'ambiante entre 1µm et 12 µm dans l'IR) sur des couches de CdHgTe réalisées par épitaxie en phase liquide (EPL) de différentes compositions en Cd ont été effectuées. La corrélation de ces mesures optiques avec des mesures électriques par effet Hall en température a permis d'identifier les énergies d'activation des 2 niveaux de la lacune de mercure ainsi que de démontrer le phénomène de U-négativité de la lacune de mercure dans le CdHgTe. De plus, la comparaison de spectres de PL d'échantillons dopés arsenic pendant la croissance par épitaxie par jets moléculaires (EJM) avec des mesures disponibles réalisées par absorption de rayons X (EXAFS) a permis d'observer des transitions optiques associées aux différents complexes arsenic formés avant et pendant le recuit d'activation. Par ailleurs, un travail de modélisation du phénomène de désordre d'alliage dans le CdHgTe a été réalisé. Plus précisément, un modèle basé sur une statistique gaussienne associée aux fluctuations d'alliage autour d'un gap moyen et une statistique de Boltzman a été développé pour ajuster dans un premier temps des spectres d'absorption puis pour ajuster les spectres de photoluminescence. Ce modèle nous a permis d'ajuster étroitement les spectres de photoluminescence et d'absorption, tout en prenant en compte intrinsèquement le désordre d'alliage du matériau. Nous avons ainsi constaté que l'ajustement des spectres par des fonctions gaussiennes comme il est réalisé communément dans la littérature permet de trouver les bons écarts entre les pics d'émission et donc les bonnes énergies d'ionisation. Dans un deuxième temps, toujours dans le cas de la détection infrarouge, le travail a porté sur l'étude du substrat CdZnTe utilisé pour l'épitaxie du CdHgTe. Des comparaisons des spectres de PL avec les paramètres de croissance ont été effectuées. Plus particulièrement, une étude sur une zone spécifique de certains échantillons présentant une absorption du rayonnement IR a été réalisée afin d'en comprendre l'origine. Enfin, nous nous sommes intéressés à la couche de CdS, matériau II-VI dopé intrinsèquement (type n) utilisé comme fenêtre transparente et formant la jonction p-n avec le CdTe dans les cellules solaires, détecteurs de lumière visible. Dans cette partie, nous avons cherché à étudier l'influence des différentes méthodes de dépôt, sublimation ou bain chimique de la couche de CdS sur un substrat de verre, en comparant les spectres d'émission de photoluminescence obtenus ainsi que les types de traitements thermiques effectués après dépôts. Ces mesures ont été corrélées avec le rendement des cellules solaires finales.
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40

Baron, Thierry. "Dopage des semiconducteurs II-VI à base de tellure et réalisation de structures quantiques." Université Joseph Fourier (Grenoble ; 1971-2015), 1996. http://www.theses.fr/1996GRE10060.

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Nous avons etudie le dopage des semiconducteurs ii-vi a base de tellure. Concernant le dopage de type n, nous avons montre que l'impurete iode est mieux adaptee que l'impurete indium, pour atteindre de fortes concentrations de porteurs dans cdte et cdznte. Le dopage de type p est realise en utilisant une cellule dc plasma, permettant d'obtenir de l'azote sous forme atomique. En comparant les proprietes electriques, optiques et structurales de znte:n et de cdte:n, nous avons mis en evidence un phenomene de compensation limitant le niveau maximum de dopage accessible pour cdte:n. Afin de comprendre l'origine de ce phenomene, nous avons entrepris l'etude du dopage des alliages cdznte et des alliages cdmgte et znmgte. A partir de cette etude, nous avons elabore un modele fonde sur la comparaison des enthalpies de formation des composes nitrures a#3n#2 (a=cd, zn, mg). La formation de tels composes limiterait la solubilite limite de l'azote en site substitutionnel actif. Ainsi, la compensation interviendrait preferentiellement dans les materiaux contenant du mg puis du cd, et serait faible pour le materiau znte. Un mecanisme complementaire, faisant intervenir le parametre de maille, a egalement ete propose. Maitrisant le dopage des tellurures, nous avons realise des heterostructures dopees par modulation afin d'etudier des gaz d'electrons bidimensionnels. En epitaxiant des puits quantiques dopes de type p, nous avons montre que la localisation de l'impurete azote dans la structure modifie les energies de liaison (i) de l'exciton lie sur un accepteur neutre et (ii) de l'accepteur. Nous avons mis en evidence, par des mesures optiques, structurales et chimiques, une acceleration de l'interdiffusion dans les superreseaux contenant a la fois du mg et de l'azote. Enfin, nous avons realise des dispositifs optoelectroniques tels que des modulateurs optiques ou des emetteurs et des detecteurs de rayonnement dans l'infrarouge
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41

Fourreau, Yohan. "Study of the structural properties and defects in CdxHg1-xTe / Cd1-yZnyTe system and investigation of technological improvements for Infrared detection at high temperature." Electronic Thesis or Diss., Paris 6, 2016. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2016PA066761.pdf.

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La problématique de qualité des images des composants matriciels IR refroidis, à base de matériaux II-VI, fait partie des enjeux critiques pour SOFRADIR. Positionnées dans un contexte très concurrentiel, cette problématique est exacerbée à hautes températures (HOT). Elle concerne en particulier les filières CdHgTe, confrontées à des instabilités en bruit de certains pixels, dits "clignotants", difficilement corrigibles. Des études internes à SOFRADIR montrent un fort degré de corrélation entre ce bruit spécifique et la défectivité (densité de dislocations) de la couche d’absorption CdHgTe. L’amélioration des performances en bruit des imageurs IR à base de matériaux II-VI passe donc par l’amélioration de la défectivité de l’alliage CdHgTe. C’est l’objet de ces travaux de thèse. Plus spécifiquement, ces travaux ont eu pour principal objectif la réduction de la densité de dislocations des couches CdHgTe(111)B élaborées par Epitaxie en Phase Liquide (EPL) sur substrats CdZnTe, dits à "accord de maille". Précisément, ces études ciblent la réduction de la défectivité inhérente au désaccord paramétrique. Ces travaux montrent que la qualité cristalline des épitaxies CdHgTe se situe à l’état de l’art mondial lorsque les croissances s’effectuent à accord paramétrique. La dégradation de la qualité cristalline des croissances est corrélée avec l’augmentation du désaccord paramétrique, au demeurant très faible dans ce système (0,1% maximum). Plusieurs solutions ont été mises en œuvre dans ces travaux pour limiter la formation de dislocations dans l’épitaxie CdHgTe. Notamment, une méthode originale d’épitaxie du CdHgTe a été développée pour permettre la croissance de couches buffers épaisses entre le substrat et l’épitaxie. L’efficacité de cette méthode a été évaluée par des caractérisations physico-chimiques approfondies des couches buffers et des épitaxies HgCdTe EPL reprises sur ces mêmes buffers. Les performances électro-optiques de composants intégrant ces empilements ont également été évaluées. D’autres stratégies technologiques ont été étudiées afin d’améliorer la défectivité des alliages CdHgTe. L’étude de substrats quaternaires CdZnTeSe à paramètre de maille constant a ainsi été adressée. La qualité cristalline de ces substrats et des épitaxies CdHgTe réalisées est proche de l’état de l’art. Ces conclusions préliminaires ouvrent des perspectives de grand intérêt technologique<br>Quality and stability issues of the images of the matrix components IR cooled with materials II-VI, in particular at high temperature with functioning is critical stakes for Sofradir in a very competitive context. In particular, CdHgTe FPAs are confronted with instabilities in noises of certain pixels, said "blinkers", dominated by a noise type RTS's low frequency (Random Telegraph Signal) difficult to correct. Works show that this specific noise is partially connected to the density of dislocations of the absorption layer, CdHgTe. The improvement of the performances in noise of imagers thus passes by the reduction of the density of dislocations of the alloy CdHgTe.More specifically, these works had for objectives the reduction of the density of dislocations stemming from the plastic relaxation of all or part of the constraints related to the lattice mismatch between the liquid-phase epitaxy (EPL) CdHgTe ( 111 ) B and its CdZnTe substrate.It is shown in these works that the crystalline quality of CdHgTe is situated in the world state of the art when the growths are made in lattice-match conditions (EPD from 9.103 to 5.104 cm-2). The degradation of the crystalline quality of epitaxy is then correlated to the increase of the lattice mismatch substrate-epitaxy, which remains very low (0,1 %). From then on, several solutions, partially stemming from the literature of the systems CdHgTe on If, GaAs or Ge, in strong lattice mismatch (&gt; 13 %), were implemented in these works to limit the formation of misfit dislocations within the CdHgTe layer. In particular, A specific method based on CdHgTe epitaxy was developed to reduce lattice mismatch between the CdZnTe substrate and the CdHgTe epitaxy. The efficiency of this method is estimated since the structural characterization CdHgTe layers, up to the analysis of the electro-optical performances of FPA components.Finally, the problem of the lattice mismatch is approached on a wider frame, in particular via the study of other II-VI-based alloys allowing the realization of lattice-match substrates for CdHgTe. The crystalline quality of these substrates and the realized CdHgTe layers is close to the state of the art. These preliminary conclusions open perspectives of big interest
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42

Zuniga-Perez, Jesús, Lars Kappei, Christiane Deparis, et al. "Homoepitaxial nonpolar (10-10) ZnO/ZnMgO monolithic microcavities: Towards reduced photonic disorder." American Institute of Physics, 2016. https://ul.qucosa.de/id/qucosa%3A23543.

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Nonpolar ZnO/ZnMgO-based optical microcavities have been grown on (10-10) m-plane ZnO substrates by plasma-assisted molecular beam epitaxy. Reflectivity measurements indicate an exponential increase of the cavity quality factor with the number of layers in the distributed Bragg reflectors. Most importantly, microreflectivity spectra recorded with a spot size in the order of 2 lm show a negligible photonic disorder (well below 1 meV), leading to local quality factors equivalent to those obtained by macroreflectivity. The anisotropic character of the nonpolar heterostructures manifests itself both in the surface features, elongated parallel to the in-plane c direction, and in the optical spectra, with two cavity modes being observed at different energies for orthogonal polarizations.
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43

Wille, Marcel, Tom Michalsky, Evgeny Krüger, Marius Grundmann, and Rüdiger Schmidt-Grund. "Absorptive lasing mode suppression in ZnO nano- and microcavities." American Institute of Physics, 2016. https://ul.qucosa.de/id/qucosa%3A23548.

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We conclusively explain the different lasing mode energies in ZnO nano- and microcavities observed by us and reported in literature. The limited penetration depth of usually used excitation lasers results in an inhomogeneous spatial gain region depending on the structure size and geometry. Hence, weakly or even nonexcited areas remain present after excitation, where modes are instantaneously suppressed by excitonic absorption. We compare the effects for ZnO microwires, nanowires, and tetrapod-like structures at room temperature and demonstrate that the corresponding mode selective effect is most pronounced for whispering-gallery modes in microwires with a hexagonal cross section. Furthermore, the absorptive lasing mode suppression will be demonstrated by correlating the spot size of the excitation laser and the lasing mode characteristic of a single ZnO nanowire.
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44

Eley, Clive William. "The rational design of photocatalytic semiconductor nanocrystals." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:ee29c922-857c-432a-8316-a7e04c822b1d.

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This thesis reports the successful rational design of three highly active photocatalytic semiconductor nanocrystal (SNC) systems by exploiting morphology effects and the electronic properties of type II semiconductor heterojunctions. Novel architectures of colloidal SNCs are produced with the aim of suppressing exciton recombination and improving charge extraction for the successful initiation of desirable redox chemistry. Rod-shaped niobium pentoxide Nb<sub>2</sub>O<sub>5</sub> nanocrystals (NCs) are shown to exhibit significantly enhanced activity (10-fold increase in rate constant) relative to spherical-shaped NCs of the same material. The increase is attributed to Nb5<sup>+</sup> Lewis acid site rich (001) surfaces, present in higher proportions in the rod morphology, which bind organic substrates from solution resulting in direct interaction with photogenerated charges on the surface of the NC. Building on the insights into morphology-activity dependence, type II semiconductor heterojunctions are exploited for their ability to increase exciton lifetimes and spatially separate charges. Two novel II-VI heterostructured semiconductor nanocrystals (HSNCs) systems are investigated: a series of CdX/ZnO (X = S, Se, Te) HSNCs and ZnS/ZnO HSNCs capped with two different surface ligands. In the first case, substantial photocatalytic activity improvement is observed for HSNCs (relative to pure ZnO analogues) according to the following trend: CdTe/ZnO > CdS/ZnO > CdSe/ZnO. The observed trend is explained in terms of heterojunction structure and fundamental chalcogenide chemistry. In the second case, both ZnS/ZnO HSNCs exhibit activity enhancement over analogous pure ZnO, but the degree of enhancement is found to be a function of surface ligand chemistry. Photocatalytic activity testing of all the materials investigated in this work is performed via the photodecomposition of methylene blue dye in aerated aqueous conditions under UVA (350 nm) irradiation. The synthetic techniques employed for the synthesis of colloidal SNCs investigated in this thesis range from chemical precipitation and solvothermal techniques to several different organometallic approaches. A wide variety of analytical techniques are employed for the chemical, structural and optical characterisation of SNC photocatalysts including: XRD, XPS, TEM, UV-vis absorption, PL spectroscopy and FTIR. Atom Probe Tomography (APT) is employed for the first time in the structural characterisation of II-VI heterojunctions in colloidal HSNCs. Overall, this thesis provides a useful contribution to the growing body of knowledge pertaining to the enhancement of photocatalytic SNCs for useful applications including: solar energy conversion to chemical fuels, the photodecomposition of pollutants and light-driven synthetic chemistry.
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45

Mordenti, Stéphane. "Etude magnéto-optique dans le proche infrarouge de systèmes bidimensionnels élaborés à partir d'alliages II-VI ou III-V." Université Joseph Fourier (Grenoble), 1997. http://www.theses.fr/1997GRE10127.

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Ce memoire presente des etudes magneto-optiques realisees dans le proche infrarouge de systemes bidimensionnels construits a partir des alliages cdhgte ou gainas. Les structures symetriques cd#yhg#1#-#yte/cd#xhg#1#-#yte ont ete etudiees sous champ magnetique (0,20 t) en luminescence et en abosorption. Les variations de formes quadratiques de la position des raies de luminescence sous champ montrent que la transition observee dans ce type de systemes fait intervenir une forte energie de liaison entre les porteurs des bandes de conduction et de valence. Nous l'avons d'ailleurs interpretee comme une transition entre donneurs et accepteurs distribues aleatoirement dans les structures. Les structures symetriques al#yin#1#-#yas/ga#xin#1#-#xyas/al#yin#1#-#yas dopees donneurs si dans les barrieres et accepteurs be au centre des puits ont permis de nombreuses analyses sous champ magnetique. Le comportement d'un gaz bidimensionnel d'electrons cree par les techniques de dopage a ete ainsi etudie a travers la recombinaison radiative entre les electrons libres et les trous lies aux accepteurs be. Les oscillations du rayon de bohr des accepteurs, causees par les variations du pouvoir d'ecrantage du gaz d'electrons 2d ont ete tres bien mises en evidence : l'etude des spectres en fonction de la temperature et du facteur de remplissage, l'evolution en fonction du champ de l'intensite totale du niveau de landau n = o montrent que pour les facteurs de remplissage pairs, l'efficacite d'ecrantage du gaz 2d presente des minimums relatifs qui generent des minimums dans les variations du rayon de bohr. Les variations du premier moment et du second moment du spectre soulignent l'interet des etudes magnetooptiques dans le cas de la transition electrons-accepteurs pour mesurer les gaps entre chaque niveau de landau apparaissant dans les etats de l'effet hall quantique.
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46

Gérard, Lionel. "Structures de semiconducteurs II-VI à alignements de bande de type II pour le photovoltaïque." Thesis, Grenoble, 2013. http://www.theses.fr/2013GRENY070.

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Ce travail porte sur l'étude d'hétérostructures de semiconducteurs II-VI à alignements de bande de type II, en particulier sous forme de superréseaux. Il s'agit d'un système qui peut être prometteur pour une application photovoltaïque, et c'est dans cette optique qu'est orienté ce travail. Une première partie traite ainsi d'une réflexion conceptuelle sur l'apport des interfaces de type II au photovoltaïque.Nous présentons ensuite une étude sur la croissance de CdSe et ZnTe par épitaxie par jets moléculaires, sur différents substrats. Ces matériaux sont particulièrement intéressants et adaptés pour cette application car ils ont un gap direct, quasiment le même paramètre de maille, un alignement de bandes de type II, et le CdSe une bande interdite compatible avec le spectre solaire. Mais en contrepartie il s'agit de semiconducteurs binaires qui n'ont aucun atome en commun, de sorte que la croissance d'échantillons avec des épaisseurs précises à la monocouche près constitue un vrai défi. Pour cette raison nous avons procédé à une étude fine des interfaces grâce à des analyses de diffraction de rayons X et de microscopie en transmission, qui nous permet de conclure sur la nature chimique des atomes à proximité des interfaces.Vient ensuite une étude poussée de spectroscopie sur les effets des interfaces de type II sur les porteurs de charges, à travers leur énergie et cinétique de recombinaison. Nous avons développé un modèle analytique qui permet d'ajuster précisément toutes les caractéristiques observées en relation avec ces interfaces, et qui témoigne d'un mécanisme de séparation des charges très efficace. Nous montrons par la suite que ces effets observés sont des caractéristiques intrinsèques de toutes les interfaces de type II, indépendamment des matériaux et des structures, et que ceux-ci nous permettent d'extraire avec précision les valeurs des décalages de bandes entre différents matériaux à alignement de type II<br>This work focuses on the study of II-VI semiconductor heterostructures with type II band alignments, especially in the form of superlattices. This is a system that can be promising for photovoltaic applications, and my work is presented in this perspective. Thus the first part deals with a conceptual reflection on the contribution of type II interfaces for photovoltaics.In a second step I present a study on the growth of CdSe and ZnTe by molecular beam epitaxy on various substrates. These materials are particularly interesting and suitable for this application because they have a direct bandgap, are almost lattice-matched, present a type II band alignment, and CdSe shows a bandgap compatible with the solar spectrum. But in return these are binary semiconductors which have no atoms in common, so that the growth of samples with specific thicknesses close to the monolayer is challenging. For this reason we conducted a detailed study at the interfaces through analysis of X-ray diffraction and transmission electron microscopy, which allows us to conclude on the chemical nature of the atoms near the interfaces.This is followed by a detailed spectroscopy study on the effects of type II interfaces on the charge carriers through their energy and kinetics of recombination. We have developed an analytical model that allows to precisely adjust all the features observed in relation to these interfaces, and shows a very efficient charge separation mechanism. We show later that these effects are inherent characteristics of all interfaces of type II, regardless of materials and structures, and that they allow us to accurately extract the values of band offsets between different materials with type II band alignments
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47

Hervé, Denis. "Étude et réalisation d'un laser à semiconducteur compact de type à pompage électronique (par micropointes) émettant dans le visible (bleu)." Université Joseph Fourier (Grenoble ; 1971-2015), 1995. http://www.theses.fr/1995GRE10076.

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L'etude d'un laser a semiconducteur de type a pompage electronique est presentee. Le but de ce travail est la realisation d'un laser compact emettant dans le visible (bleu). Deux aspects distincts ont ete consideres. 1 le pompage electronique du laser ainsi que la realisation d'un dispositif compact. Le faisceau d'electrons permettant le pompage du laser est obtenu a partir d'une cathode comportant des micropointes. Ce composant est une source d'electrons froide, utilisant le principe de l'emission par effet de champ, realise grace aux procedes de la microelectronique conventionnelles et deja utilise dans la fabrication d'ecrans plats. Les travaux presentes relatent l'etude des caracteristiques de ces sources et de leur interet dans le cadre de ce projet. La focalisation du faisceau d'electrons est decrites dans plusieurs cas de figure, et la realisation d'un dispositif compact scelle sous vide statique fonctionnant en mode cathodoluminescent est rapportee. 2 laser semiconducteur ii-vi a grand gap permettant l'emission lumineuse dans le visible. Les heterostructures laser doivent etre specialement adaptees au pompage electronique a cause de la relativement faible profondeur de penetration des electrons pour les energies considerees. La description du fonctionnement des lasers semiconducteurs est donnees dans un premier temps. Il apparait que pour notre application, les structures laser doivent etre de type grinsch (heterostructure a gradient de composition et a separation des confinements) a puits quantiques. Dans un deuxieme temps, les resultats de caracterisation des materiaux laser, par les techniques de cathodoluminescence, de microscopie, de spectroscopie de masse des ions secondaires (sims) et de pompage electronique sont donnes. L'evolution des seuils en fonction de la temperature et les problemes de duree de vie en fonctionnement des lasers semiconducteurs sont plus particulierement traites. Ces resultats sont compares a ceux des diodes laser ii-vi actuelles
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48

Graham, Timothy Carl Maxwell. "Spectroscopy of II-VI semiconductor quantum dots." Thesis, Heriot-Watt University, 2006. http://hdl.handle.net/10399/103.

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49

Zhao, Lijuan. "Chemical syntheses and characterizations of II-VI semiconductor nanocrystals /." View abstract or full-text, 2007. http://library.ust.hk/cgi/db/thesis.pl?PHYS%202007%20ZHAO.

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50

Benallali, Hammouda. "Étude de nanostructures de semiconducteurs II-VI par sonde atomique tomographique." Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM4324.

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Les nanostructures de semiconducteurs II-VI ont de nombreuses applications en microélectronique, optoélectronique et photonique. Notamment, les boites quantiques II-V peuvent servir de source de photons uniques. Dans cette étude, nous nous sommes intéressés à la caractérisation chimique et structurale des nanostructures de semiconducteurs II-VI (boites quantiques (BQs) auto-organisées, nanofils II-VI et III-V …) par sonde atomique tomographique (SAT). Dans un premier temps, nous avons optimisé les conditions d’analyse des semiconducteurs III-V et II-VI par SAT. Ensuite, nous avons étudié les compositions chimiques des interfaces II-VI/III-V en montrant la formation d’un composé Ga2.7Se3 à l’interface ZnSe/GaAs et un mélange de cations (Ga, Zn) à l’interface ZnTe/InAs. Les mesures de compositions chimiques et des tailles des boites quantiques en trois dimensions par SAT ont permis de faire une corrélation avec les mesures optiques. Nous nous sommes aussi intéressés à l’étude des mécanismes de croissance des nanofils GaAs et ZnTe ainsi que des BQs (CdTe) insérés dans des nanofils ZnTe en analysant la composition chimique des catalyseurs, les BQs dans les nanofils aussi que la base des nanofils. Ces mesures montrent que les boites quantiques sont formées d’un fort mélange CdxZn1-xTe. Un scénario basé sur la diffusion de surface a été proposé pour expliquer la croissance ainsi que le mélange entre Zn/Cd pour les BQs insérées dans les nanofils<br>Nanostructures of II-VI nanostructure have many applications in microelectronics, optoelectronics and photonics. For example, II -V quantum dots have shown the ability to be a source of single photons. In this work, we performed in the chemical and structural characterization of nanostructures of II-VI semiconductors (self- organized quantum dots (QDs), nanowires II-VI and III- V ...) by atom probe tomography (APT). Firstly, the analysis conditions of III-V and II- VI semiconductors by APT were optimized. Then, we studied the chemical composition of II-VI/III-V interfaces and showed the formation of a Ga2.7Se3 compound at the ZnSe/GaAs interface and the (Ga, Zn) cations mixing at the ZnTe/InAs interface. The measurements of the chemical composition and the sizes of quantum dots in three dimensions by APT allowed making a correlation with optical measurements. We studied also growth mechanisms of GaAs, ZnTe nanowire and the CdTe QDs inserted in ZnTe nanowires by analyzing the chemical composition of the catalysts QDs and nanowires basis. These measurements show that the quantum dots are formed of a strong mixing of CdxZn1-xTe. A scenario based on surface diffusion has been proposed to explain the growth and the mixing between Zn/Cd for the QDs
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