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Dissertations / Theses on the topic 'Doped semiconductors. Diluted magnetic semiconductors'

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Published: 4 June 2021
Last updated: 11 February 2022

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1

Gatuna, Ngigi wa. "Intrinsic vacancy chalcogenides as dilute magnetic semiconductors : theoretical investigation of transition-metal doped gallium selenide /." Thesis, Connect to this title online; UW restricted, 2007. http://hdl.handle.net/1773/10595.

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2

Liu, William K. "Electron spin dynamics in quantum dots, and the roles of charge transfer excited states in diluted magnetic semiconductors /." Thesis, Connect to this title online; UW restricted, 2007. http://hdl.handle.net/1773/8588.

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3

Fan, Junpeng. "Synthesis and advanced structural and magnetic characterization of mesoporous transition metal–doped sno2 powders and films." Doctoral thesis, Universitat Autònoma de Barcelona, 2017. http://hdl.handle.net/10803/457982.

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Aquesta Tesi doctoral comprèn la síntesi mitjançant nanoemmotllament (de l’anglès, nanocasting) i autoassemblatge per evaporació induïda (de l’anglès, evaporation–induced self–assembly) i la caracterització exhaustiva de pols i capes de SnO2 mesoporós dopat amb Ni i Cu. L’origen de les propietats magnètiques d’aquests materials es discuteix en detall. En primer lloc, es van sintetitzar per nanoemmotllament a partir de motlles de sílice KIT–6, pols mesoporosa ordenada de SnO2 dopada amb diferents quantitats de Ni. Es va verificar la replicació correcta del motlle de sílice mitjançant microscòpia electrònica de rastreig. No es van detectar fases extres atribuïbles a Ni o NiO en els corresponents difractogrames excepte per a la mostra amb el dopatge més alt (9 at.% Ni), per a la qual es va observar la presència de NiO com a fase secundària. Es va estudiar l’estat d’oxidació i la distribució espaial de Ni en la pols mitjançant espectroscòpia fotoelectrònica de raigs X i espectroscòpia de pèrdua d’energia d’electrons, respectivament. Les mostres dopades amb Ni presenten resposta ferromagnètica tant a temperatura ambient com a baixa temperatura, com a conseqüència de la presència d’espins no compensats a la superfície de nanopartícules de NiO i vacants d’oxigen. En segon lloc, es van sintetitzar capes primes continues i mesoporoses de SnO2 dopades amb Ni a partir de diferents relacions molars [Ni(II)]/[Sn(IV)] mitjançant un procés d’autoassemblatge sol–gel, utilitzant el copolímer tribloc P–123 com a agent director d’estructura. Una caracterització estructural profunda va evidenciar l’obtenció d’una estructura nanoporosa 3–D, de gruix comprès entre els 100 i 150 nm, i mida de porus de 10 nm. Els experiments de difracció de raigs X d’incidència rasant van posar de manifest que el Ni ocupava posicions substitucionals en la xarxa tipus rutil del SnO2, tot i que les anàlisis per dispersió d’energies de raigs X també van revelar la presència de petits clústers de NiO en les capes produïdes a partir de les relacions molars [Ni(II)]/[Sn(IV)] més elevades. Convé remarcar que les propietats magnètiques de les capes mesoporoses varien significativament en funció del percentatge de dopant. Les capes de SnO2 no dopades presenten un comportament diamagnètic, mentre que les dopades amb Ni mostren un clar senyal paramagnètic amb una petita contribució ferromagnètica. En tercer lloc, també es van estudiar les propietats magnètiques de pols mesoporosa ordenada de SnO2 dopada amb Cu, obtinguda mitjançant nanoemmotllament a partir de sílice KIT–6. Per bé que una eventual contaminació amb impureses de Fe or la presència de vacants d’oxigen podrien explicar el comportament ferromagnètic observat a temperatura ambient, el ferromagnetisme a baixa temperatura es va atribuir únicament a la naturalesa nanoestructurada de les nanopartícules antiferromagnètiques de CuO formades (espins no compensats i shape–mediated spin canting). La menor temperatura de bloqueig, situada entre 30 i 50 K, i l’existència de petits desplaçaments verticals en els cicles d’histèresi van confirmar efectes de mida en les nanopartícules de CuO
This Thesis dissertation covers the synthesis by means of nanocasting and evaporation–induced self–assembly (EISA) methods as well as the advanced characterization of Ni, Cu–doped mesoporous SnO2 powders and films. The origin of the magnetic properties in these materials is also discussed in detail. Firstly, ordered mesoporous SnO2 powders doped with different Ni amounts were synthesized by nanocasting from mesoporous KIT–6 silica. Successful replication of the silica template was verified by scanning electron microscopy. No extra phases attributed to Ni or NiO were detected in the corresponding X–ray diffractograms except for the sample with the highest doping amount (e.g., 9 at.% Ni), for which NiO as secondary phase was observed. The oxidation state and spatial distribution of Ni in the powders was investigated by X–ray photoelectron spectroscopy and electron energy loss spectroscopy, respectively. Ni–containing powders exhibit ferromagnetic response at low and room temperatures, due to uncompensated spins at the surface of NiO nanoparticles and the occurrence of oxygen vacancies. Secondly, continuous mesoporous Ni–doped SnO2 thin films were synthesized from variable [Ni(II)]/[Sn(IV)] molar ratios through a sol–gel based self–assembly process, using P–123 triblock copolymer as a structure directing agent. A deep structural characterization revealed a truly 3–D nanoporous structure with thickness in the range of 100–150 nm, and average pore size about 10 nm. Grazing incidence X–ray diffraction experiments indicated that Ni had successfully substituted Sn in the rutile–type lattice, although energy–dispersive X–ray analyses also revealed the occurrence of small NiO clusters in the films produced from high [Ni(II)]/[Sn(IV)] molar ratios. Interestingly, the magnetic properties of these mesoporous films significantly vary as a function of the doping percentage. The undoped SnO2 films exhibit a diamagnetic behaviour, whereas a clear paramagnetic signal with small ferromagnetic contribution dominates the magnetic response of the Ni–doped mesoporous films. Thirdly, the magnetic properties of ordered mesoporous Cu–doped SnO2 powders, prepared by hard–templating from KIT–6 silica, were also studied. While Fe contamination or the presence of oxygen vacancies might be a plausible explanation of the room temperature ferromagnetism, the low–temperature ferromagnetism was mainly and uniquely assigned to the nanoscale nature of the formed antiferromagnetic CuO nanoparticles (uncompensated spins and shape–mediated spin canting). The reduced blocking temperature, which resided between 30 and 5 K, and small vertical shifts in the hysteresis loops confirmed size effects in the CuO nanoparticles.
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4

Kaspar, Tiffany C. "Materials and magnetic studies of cobalt-doped anatase titanium dioxide and perovskite strontium titanate as potential dilute magnetic semiconductors /." Thesis, Connect to this title online; UW restricted, 2004. http://hdl.handle.net/1773/9902.

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5

Rumaiz, Abdul K. "Cobalt doped titanium dioxide, a possible candidate for dilute magnetic semiconductor." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 149 p, 2008. http://proquest.umi.com/pqdweb?did=1459915881&sid=3&Fmt=2&clientId=8331&RQT=309&VName=PQD.

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6

Yang, Zihao. "Magneto and Spin Transport in Magnetically Doped Semiconductors and Magnetic Insulators." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1502963926201783.

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7

Chey, Chan Oeurn. "Synthesis of ZnO and transition metals doped ZnO nanostructures, their characterization and sensing applications." Doctoral thesis, Linköpings universitet, Fysik och elektroteknik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-113237.

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Nanotechnology is a technology of the design and the applications of nanoscale materials with their fundamentally new properties and functions. Nanosensor devices based on nanomaterials provide very fast response, low-cost, long-life time, easy to use for unskilled users, and provide high-efficiency. 1-D ZnO nanostructures materials have great potential applications in various sensing applications. ZnO is a wide band gap (3.37 eV at room temperature) semiconductor materials having large exciton binding energy (60 meV) and excellent chemical stability, electrical, optical, piezoelectric and pyroelectric properties. By doping the transition metals (TM) into ZnO matrix, the properties of ZnO nanostructures can be tuned and its room  temperature ferromagnetic behavior can be enhanced, which provide the TM-doped ZnO nanostructures as promising candidate for optoelectronic, spintronics and high performance sensors based devices. The synthesis of ZnO and TM-doped ZnO nanostructures via the low temperature hydrothermal method is considered a promising technique due to low cost, environmental friendly, simple solution process, diverse 1-D ZnO nanostructures can be achieved, and large scale production on any type of substrate, and their properties can be controlled by the growth parameters. However, to synthesize 1-D ZnO and TM-doped ZnO nanostructures with controlled shape, structure and uniform size distribution on large area substrates with desirable properties, low cost and simple processes are of high interest and it is a big challenge at present. The main purpose of this dissertation aims to develop new techniques to synthesize 1-D ZnO and (Fe, Mn)-doped ZnO nanostructures via the hydrothermal method, to characterize and to enhance their functional properties for developing sensing devices such as biosensors for clinical diagnoses and environmental monitoring applications, piezoresistive sensors and UV photodetector. The first part of the dissertation deals with the hydrothermal synthesis of ZnO nanostructures with controlled shape, structure and uniform size distribution under different conditions and their structural characterization. The possible parameters affecting the growth which can alter the morphology, uniformity and properties of the ZnO nanostructures were investigated. Well-aligned ZnO nanorods have been fabricated for high sensitive piezoresistive sensor. The development of creatinine biosensor for clinical diagnoses purpose and the development of glucose biosensor for indirect determination of mercury ions for an inexpensive and unskilled users for environmental monitoring applications with highly sensitive, selective, stable, reproducible, interference resistant, and fast response time have been fabricated based on ZnO nanorods. The second part of the dissertation presents a new hydrothermal synthesis of (Fe, Mn)-doped-ZnO nanostructures under different preparation conditions, their properties characterization and the fabrication of piezoresistive sensors and UV photodetectors based devices were demonstrated. The solution preparation condition and growth parameters that influences on the morphology, structures and properties of the nanostructures were investigated. The fabrication of Mn-doped-ZnO NRs/PEDOT:PSS Schottky diodes used as high performance piezoresistive sensor and UV photodetector have been studied and Fe-doped ZnO NRs/FTO Schottky diode has also been fabricated for high performance of UV photodetector. Finally, a brief outlook into future challenges and relating new opportunities are presented in the last part of the dissertation.
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8

Haider, Muhammad Baseer. "Surface and Bulk Properties of Magnetically Doped GaN and Their Dependence on the Growth Conditions." Ohio University / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1132011994.

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9

Ramanathan, Sivakumar. "Optical and electrical properties of compound and transition metal doped compound semiconductor nanowires." VCU Scholars Compass, 2009. http://scholarscompass.vcu.edu/etd/1667.

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Nanotechnology is the science and engineering of creating functional materials by precise control of matter at nanometer (nm) length scale and exploring novel properties at that scale. It is vital to understand the quantum mechanical phenomena manifested at nanometer scale dimensions since that will enable us to precisely engineer quantum mechanical properties to realize novel device functionalities. This dissertation investigates optical and electronic properties of compound and transition metal doped compound semiconductor nanowires with a view to exploiting them for a wide range of applications in semiconductor electronic and optical devices. In this dissertation work, basic concepts of optical and electronic properties at low dimensional structures will be discussed in chapter 1. Chapter 2 discusses the nanofabrication technique employed to fabricate highly ordered nanowires. Using this method, which is based on electrochemical self-assembly techniques, we can fabricate highly ordered and size controlled nanowires and quantum dots of different materials. In Chapter 3, we report size dependent fluorescence spectroscopy of ZnSe and Mn doped ZnSe nanowires fabricated by the above method. The nanowires exhibit blue shift in the emission spectrum due to quantum confinement effect, which increases the effective bandgap of the semiconductor. We found that the fluorescence spectrum of Mn doped ZnSe nanowires shows high luminescence efficiency, which seems to increase with increasing Mn concentration. These results are highly encouraging for applications in multi spectral displays. Chapter 4 investigates field emission results of highly ordered 50 nm tapered ZnO nanowires that were also fabricated by electrochemical self-assembly. Subsequent to fabrication, the nanowires tips are exposed by chemical etching which renders the tips conical in shape. This tapered shape concentrates the electric field lines at the tip of the wires, and that, in turn, increases the emission current density while lowering the threshold field for the onset of field emission. Measurement of the Fowler-Nordheim tunneling current carried out in partial vacuum indicates that the threshold electric field for field emission in 50-nm diameter ZnO nanowires is 15 V/µm. In this study we identified the key constraint that can increase the threshold field and reduce emission current density. In Chapter 5 we report optical and magnetic measurement of Mn-doped ZnO nanowires. Hysterisis measurements carried out at various temperatures show a ferromagnetic behavior with a Curie temperature of ~ 200 K. We also studied Mn-doping of the ZnO nanowires. The room temperature fluorescence spectroscopy of Mn-doped ZnO nanowires shows a red-shift in the spectra compared to the undoped ZnO nanowires possibly due to strain introduced by the dopants in the nanowires. Finally, in Chapter 6, we report our study of the ensemble averaged transverse spin relaxation time (T2*) in InSb thin films and nanowires using electron spin resonance (ESR) measurement. Unfortunately, the nanowires contained too few spins to produce a detectable signal in our apparatus, but the thin films contained enough spins (> 109/cm2) to produce a measurable ESR signal. We found that the T2* decreases rapidly with increasing temperature between 3.5 K and 20 K, which indicates that spin-dephasing is primarily caused by spin-phonon interactions.
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10

Tran, Lien. "InSb semiconductors and (In,Mn)Sb diluted magnetic semiconductors." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2011. http://dx.doi.org/10.18452/16334.

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Im Rahmen dieser Arbeit wurden InSb- und verdünnt-magnetische In_{1-x}Mn_xSb Filme mittels Gasquellen-Molekularstrahlepitaxie hergestellt und deren strukturelle und elektronische Eigenschaften untersucht. Die 2 μm InSb-Dünnschichten wurden sowohl auf GaAs(001)-Substrat als auch um 4° in Richtung [110] fehlgeschnittenem Si(001)-Substrat hergestellt. Optimierte InSb-Schichten direkt auf GaAs zeigen eine hohe kristalline Qualität, niedriges Rauschen und eine Elektronenbeweglichkeit von 41100 cm^2/Vs bei 300 K. Die Ladungsträgerkonzentration beträgt etwa 2,9e16 cm^{-3}. Um InSb-Dünnschichten guter Qualität auf Si-Substrat zu realisieren, wurden fehlgeschnittene Substrate benutzt. Zur Reduzierung der Gitterfehlanpassung wurden Pufferschichten gewachsen. Eine Elektronenmobilität von 24000 cm^2/Vs und Ladungsträgerkonzentration von 2,6e16 cm^{-3} wurden bei 300 K nachgewiesen. Diese Probe enthält ein 0,06 μm GaAs/AlSb-Supergitter als Pufferschicht (Wachstumstemperatur war 340°C). Diese Probe zeigt der höheren Dichte der Microtwins und Stapelfehler als auch den Threading-Versetzungen in der schnittstellennahen Region geschuldet. Die Deep-Level Rauschspektren zeigen die Existenz von Deep-Levels sowohl in GaAs- als auch in Si-basierten Proben. Die InSb-Filme auf Si-Substrat zeigen einen kleineren Hooge-Faktor im Vergleich zu Schichten auf GaAs (300 K). Unter Anwendung der optimierten Wachstumsbedingungen für InSb/GaAs wurden verdünnt-magnetische In_{1-x}Mn_xSb-Schichten (bis zum 1% Mangan) auf GaAs (001)-realisiert. Mn verringert die Gitterkonstante und damit den Grad der Relaxation von (In,Mn)Sb-Filmen. In den Proben befindet sich Mn in zwei magnetischen Formen, sowohl als verdünnt-magnetischer Halbleiter (In,Mn)Sb, als auch als MnSb-Cluster. Die Cluster dominieren auf der Oberfläche. Die Curie-Temperatur, Tc, unterscheidet sich für die beiden Formen. Für (In,Mn)Sb ist Tc kleiner als 50 K. Die MnSb-Cluster zeigen dagegen ein Tc über 300 K.
This dissertation describes the growth by molecular beam epitaxy and the characterization of the semiconductor InSb and the diluted magnetic semiconductor (DMS) In_{1-x}Mn_xSb. The 2 µm-thick InSb films were grown on GaAs (001) substrate and Si (001) offcut by 4° toward (110) substrate. After optimizing the growth conditions, the best InSb films grown directly on GaAs results in a high crystal quality, low noise, and an electron mobility of 41100 cm^2/V s Vs with associated electron concentration of 2.9e16 cm^{-3} at 300 K. In order to successfully grow InSb on Si, tilted substrates and the insertion of buffer layers were used. An electron mobility of 24000 cm^2/V s measured at 300 K, with an associated carrier concentration of 2.6e16 cm^{-3} is found for the best sample that was grown at 340°C with a 0.06 μm-thick GaSb/AlSb superlattice buffer layer. The sample reveals a density of microtwins and stacking faults as well as threading dislocations in the near-interface. Deep level noise spectra indicate the existence of deep levels in both GaAs and Si-based samples. The Si-based samples exhibit the lowest Hooge factor at 300 K, lower than the GaAs-based samples. Taking the optimized growth conditions of InSb/GaAs, the DMS In_{1-x}Mn_xSb/GaAs is prepared by adding Mn (x < 1%) into the InSb during growth. Mn decreases the lattice constant as well as the degree of relaxation of (In,Mn)Sb films. Mn also distributes itself to result in two different and distinct magnetic materials: the DMS (In,Mn)Sb and clusters MnSb. The MnSb clusters dominate only on the surface. For the DMS alloy (In,Mn)Sb, the measured values of Curie temperature Tc appears to be smaller than 50 K, whereas it is greater than 300 K for the MnSb clusters.
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11

Wang, Weigang. "Spin-dependent transport in magnetic tunnel junctions and diluted magnetic semiconductors." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 184 p, 2009. http://proquest.umi.com/pqdweb?did=1654494821&sid=3&Fmt=2&clientId=8331&RQT=309&VName=PQD.

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12

Huang, Lunmei. "Computational Material Design : Diluted Magnetic Semiconductors for Spintronics." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-7800.

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13

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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14

Peleckis, Germanas. "Studies on diluted oxide magnetic semiconductors for spin electronic applications." Access electronically, 2006. http://www.library.uow.edu.au/adt-NWU/public/adt-NWU20070821.145447/index.html.

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15

Brieler, Felix [Verfasser]. "Nanostructured diluted magnetic semiconductors within mesoporous silica / Felix Brieler." Gießen : Universitätsbibliothek, 2012. http://d-nb.info/1063954878/34.

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16

Miao, Jingqi. "The theory of magnetic polarons and magnetic field effect in diluted magnetic semiconductors." Thesis, University of Hull, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.264955.

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17

Mishra, Subodha. "Theory of photo-induced ferro-magnetism in dilute magnetic semiconductors." Diss., Columbia, Mo. : University of Missouri-Columbia, 2006. http://hdl.handle.net/10355/4413.

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Thesis (Ph. D.) University of Missouri-Columbia, 2006.
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on August 6, 2007) Includes bibliographical references.
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18

Norberg, Nicholas S. "Magnetic nanocrystals : synthesis and properties of diluted magnetic semiconductor quantum dots /." Thesis, Connect to this title online; UW restricted, 2006. http://hdl.handle.net/1773/8625.

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19

Owen, Man Hon Samuel. "Electrical gating effects on the magnetic properties of (Ga,Mn)As diluted magnetic semiconductors." Thesis, University of Cambridge, 2010. https://www.repository.cam.ac.uk/handle/1810/228705.

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The aim of the research project presented in this thesis is to investigate the effects of electrostatic gating on the magnetic properties of carrier-mediated ferromagnetic Ga1-xMnxAs diluted magnetic semiconductors. (Ga,Mn)As can be regarded as a prototype material because of its strong spin-orbit coupling and its crystalline properties which can be described within a simple band structure model. Compressively strained (Ga,Mn)As epilayer with more complex in-plane competing cubic and uniaxial magnetic anisotropies is of particular interest since a small variation of these competing anisotropy fields provide a means for the manipulation of its magnetization via external electric field. An all-semiconductor epitaxial p-n junction field-effect transistor (FET) based on low-doped Ga0.975Mn0.025As was fabricated. It has an in-built n-GaAs back-gate, which, in addition to being a normal gate, enhances the gating effects, especially in the depletion of the epilayer, by decreasing the effective channel thickness by means of a depletion region. A shift in the Curie temperature of ~2 K and enhanced anisotropic magnetoresistance (AMR) (which at saturation reaches ~30%) is achieved with a depletion of a few volts. Persistent magnetization switchings with short electric field pulses are also observed. The magnitude of the switching field is found to decrease with increasing depletion of the (Ga,Mn)As layer. By employing the k . p semiconductor theory approach (performed by our collaborators in Institute of Physics, ASCR, Prague), including strong spin-orbit coupling effects in the host semiconductor valence band, a change in sign of Kc at hole density of approximately 1.5x1020 cm-3 is observed. Below this density, the [110]/[1⁻10] magnetization directions are favoured, consistent with experimental data. A double-gated FET, with an ionic-gel top-gate coupled with a p-n junction back-gate based on the same material, was also employed in an attempt to achieve larger effects through gating. It reaffirms the results obtained and demonstrates enhanced gating effects on the magnetic properties of (Ga,Mn)As.
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20

Herwadkar, Aditi Dr. "Electronic structure and magnetism in some transition metal nitrides: MN-doped ScN, dilute magnetic semiconductor and CrN, Mott insulator." Case Western Reserve University School of Graduate Studies / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=case1164816868.

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21

De, Ranieri Elisa. "Strain-induced effects on the magnetotransport properties of GaMnAs diluted magnetic semiconductors." Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.608470.

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22

Radovanovic, Pavle V. "Synthesis, spectroscopy, and magnetism of diluted magnetic semiconductor nanocrystals /." Thesis, Connect to this title online; UW restricted, 2004. http://hdl.handle.net/1773/8494.

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23

Liu, Mingde. "Magnetization-steps spectroscopy in dilute magnetic semiconductors and in molecular magnetism /." Thesis, Connect to Dissertations & Theses @ Tufts University, 1998.

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Thesis (Ph.D.)--Tufts University, 1998 .
Adviser: Yaacov Shapira. Submitted to the Dept. of Physics. Includes bibliographical references. Access restricted to members of the Tufts University community. Also available via the World Wide Web;
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24

Herwadkar, Aditi A. "Electronic structure and magnetism in some transition metal nitrides Mn-doped ScN, dilute magnetic semiconductor and CrN, Mott insulator /." online version, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=case1164816868.

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25

Bergqvist, Lars. "Electronic Structure and Statistical Methods Applied to Nanomagnetism, Diluted Magnetic Semiconductors and Spintronics." Doctoral thesis, Uppsala University, Department of Physics, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-5732.

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This thesis is divided in three parts. In the first part, a study of materials aimed for spintronics applications is presented. More specifically, calculations of the critical temperature in diluted magnetic semiconductors (DMS) and half-metallic ferromagnets are presented using a combination of electronic structure and statistical methods. It is shown that disorder and randomness of the magnetic atoms in DMS materials play a very important role in the determination of the critical temperature.

The second part treats materials in reduced dimensions. Studies of multilayer and trilayer systems are presented. A theoretical model that incorporates interdiffusion in a multilayer is developed that gives better agreement with experimental observations. Using Monte Carlo simulations, the observed magnetic properties in the trilayer system Ni/Cu/Co at finite temperatures are qualitatively reproduced.

In the third part, electronic structure calculations of complex Mn-based compounds displaying noncollinear magnetism are presented. The calculations reproduce with high accuracy the observed magnetic properties in these compounds. Furthermore, a model based on the electronic structure of the necessary conditions for noncollinear magnetism is presented.

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26

Titov, Andrey. "Electronic properties of the diluted magnetic semiconductors : Ga1-xMnxN, Ga1-xMnxAs, Ge1-xMnx." Université Joseph Fourier (Grenoble), 2006. http://www.theses.fr/2006GRE10285.

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Les propriétés électroniques de (Ga,Mn)N ont été étudiées par spectroscopie d'absorption des rayons X au seuil K du Mn. Des calculs ab-initio ont été utilisés pour interpréter les spectres d'absorption de (Ga,Mn)N. Deux pré-pics sont présents dans le seuil du Mn: le premier pré-pic est attribué aux transitions électronique vers les états 3d du Mn de spin up, tandis que le second pré-pic correspond aux transitions vers les états 3d du Mn de spin down. Cette interprétation nous permet de déterminer que l'état électronique du Mn dans (Ga,Mn)N est Mn3+: deux pré-pics sont présents dans les spectres d'absorption du Mn3+ et un seul pré-pic reste dans les spectres du Mn2+. Ce changement des spectres a été vérifié expérimentalement sur des échantillons de (Zn,Mn2+)Te et (Ga,Mn2+)As. De plus, cette interprétation permet d'étudier la distribution du Mn dans (Ga,Mn)N: la forme des spectres d'absorption suggère que la distribution du Mn est homogène dans nos échantillons de (Ga,Mn)N
Electronic properties of the diluted magnetic semiconductor (Ga,Mn)N were studied by x-ray absorption spectroscopy at the K-edge of Mn. The measured x-ray absorption spectra were further interpreted using the ab-initio calculations. Two pre-edge absorption lines are observed in the x-ray absorption spectra: the first line was attributed to electronic transitions into 3d states of Mn of spin up, while the second line corresponds to transitions into 3d states of Mn of spin down. This interpretation allows us to determine the valence state of Mn: two absorption lines are present in the pre-edge structure of Mn3+ and only one line remains in case of Mn2+. Such a change of the pre-edge structure was checked experimentally on (Zn,Mn2+)Te and on (Ga,Mn2+)As. In addition, the distribution of Mn in (Ga,Mn)N can be studied using the interpretation: the shape of the spectra points to a homogeneous distribution of Mn in our (Ga,Mn)N samples
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Mak, Chee-Leung. "Light scattering study of the diluted magnetic semiconductors Zn1-xCoxSe and Zn1-xFexSe /." The Ohio State University, 1993. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487843688959851.

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Ali, Bakhtyar. "Study of titanium dioxide based dilute magnetic semiconductors the role of defects and dopants /." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 85 p, 2008. http://proquest.umi.com/pqdweb?did=1597633311&sid=20&Fmt=2&clientId=8331&RQT=309&VName=PQD.

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Stanciu, Victor. "Magnetism of Semiconductors and Metallic Multilayers." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-5844.

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Tran, Lien [Verfasser], T. [Akademischer Betreuer] Masselink, H. [Akademischer Betreuer] Riechert, and G. [Akademischer Betreuer] Salamo. "InSb semiconductors and (In,Mn)Sb diluted magnetic semiconductors : growth and properties / Lien Tran. Gutachter: T. Masselink ; H. Riechert ; G. Salamo." Berlin : Humboldt Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2011. http://d-nb.info/1015081541/34.

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Sun, Yongke. "Theoretical studies of the electronic, magneto-optical, and transport properties of diluted magnetic semiconductors." [Gainesville, Fla.] : University of Florida, 2005. http://purl.fcla.edu/fcla/etd/UFE0011604.

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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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Bombeck, Michael [Verfasser], Manfred [Akademischer Betreuer] Bayer, and Metin [Gutachter] Tolan. "High frequency magneto-acoustics in diluted magnetic semiconductors / Michael Bombeck. Betreuer: Manfred Bayer. Gutachter: Metin Tolan." Dortmund : Universitätsbibliothek Dortmund, 2014. http://d-nb.info/1101476400/34.

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Bombeck, Michael [Verfasser], Manfred Akademischer Betreuer] Bayer, and Metin [Gutachter] [Tolan. "High frequency magneto-acoustics in diluted magnetic semiconductors / Michael Bombeck. Betreuer: Manfred Bayer. Gutachter: Metin Tolan." Dortmund : Universitätsbibliothek Dortmund, 2014. http://nbn-resolving.de/urn:nbn:de:101:1-201605242288.

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Wang, Jie. "Carrier concentration determination in GaMnAs by optical techniques /." View abstract or full-text, 2006. http://library.ust.hk/cgi/db/thesis.pl?PHYS%202006%20WANGJ.

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Guo, Bicheng. "Chemical synthesis and characterization of CdMnS and CdMnSe quantum dots /." View abstract or full-text, 2004. http://library.ust.hk/cgi/db/thesis.pl?PHYS%202004%20GUO.

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Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2004.
Includes bibliographical references (leaves 63-66). Also available in electronic version. Access restricted to campus users.
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Walsh, Kevin Anthony Peter. "Relaxation and field-cycling nuclear magnetic resonance studies of doped III-V semiconductors." Thesis, University of Surrey, 1992. http://epubs.surrey.ac.uk/843507/.

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Nuclear Magnetic Resonance Field Cycling has been further developed as a spectroscopy for impurities in III-V semiconductors. It has been used to investigate the quadrupolar and hyperfine interactions around impurity sites in GaAs and InP. Large low field relaxation peaks in the range 0 to 100 Gauss have been observed in matrix nuclei resulting from deep level impurities and broader peaks up to 1000 Gauss from shallow level impurities. The temperature dependences, from 4K to 300K, of the spin-lattice relaxation times of the matrix nuclei in doped III-V semiconductors have been measured and interpreted in terms of Korringa and quadrupolar relaxation. A detailed theory of the field-cycling experiments based on the cross-coupling of energy levels of the matrix nuclei has been developed. In addition, the spin-lattice relaxation rates have been used to understand the dynamics of cross-coupling. Anomalous field-cycling spectra have been observed in optically irradiated InP:Co and low frequency (< 1MHz) irradiated InP:S. These have been investigated in depth and possible models to interpret the results have been developed. Finally, a system has been designed and constructed to investigate NMR and related phenomena in two-dimensional electron gas systems.
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Zhou, Shengqiang. "Transition metal implanted ZnO: a correlation between structure and magnetism." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2008. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1209998012687-36583.

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Nowadays ferromagnetism is often found in potential diluted magnetic semiconductor systems. However, many authors question the origin of this ferromagnetism, i.e. if the observed ferromagnetism stems from ferromagnetic precipitates rather than from carriermediated magnetic coupling of ionic impurities, as required for a diluted magnetic semiconductor. In this thesis, this question will be answered for transition-metal implanted ZnO single crystals. Magnetic secondary phases, namely metallic Fe, Co and Ni nanocrystals, are formed inside ZnO. They are - although difficult to detect by common approaches of structural analysis - responsible for the observed ferromagnetism. Particularly Co and Ni nanocrystals are crystallographically oriented with respect to the ZnO matrix. Their structure phase transformation and corresponding evolution of magnetic properties upon annealing have been established. Finally, an approach, pre-annealing ZnO crystals at high temperature before implantation, has been demonstrated to sufficiently suppress the formation of metallic secondary phases.
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Cygorek, Moritz [Verfasser], and Vollrath Martin [Akademischer Betreuer] Axt. "Quantum kinetic description of the spin dynamics in diluted magnetic semiconductors / Moritz Cygorek ; Betreuer: Vollrath Martin Axt." Bayreuth : Universität Bayreuth, 2017. http://d-nb.info/1127127349/34.

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Linneweber, Thorben [Verfasser], Ute [Akademischer Betreuer] Löw, and Florian [Gutachter] Gebhard. "Ab-initio Gutzwiller-DFT studies of diluted magnetic semiconductors / Thorben Linneweber ; Gutachter: Florian Gebhard ; Betreuer: Ute Löw." Dortmund : Universitätsbibliothek Dortmund, 2016. http://d-nb.info/1128401169/34.

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Linneweber, Thorben [Verfasser], Ute Akademischer Betreuer] Löw, and Florian [Gutachter] [Gebhard. "Ab-initio Gutzwiller-DFT studies of diluted magnetic semiconductors / Thorben Linneweber ; Gutachter: Florian Gebhard ; Betreuer: Ute Löw." Dortmund : Universitätsbibliothek Dortmund, 2016. http://nbn-resolving.de/urn:nbn:de:101:1-20170324909.

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Zhou, Shengqiang. "Transition metal implanted ZnO: a correlation between structure and magnetism." Doctoral thesis, Technische Universität Dresden, 2007. https://tud.qucosa.de/id/qucosa%3A23718.

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Nowadays ferromagnetism is often found in potential diluted magnetic semiconductor systems. However, many authors question the origin of this ferromagnetism, i.e. if the observed ferromagnetism stems from ferromagnetic precipitates rather than from carriermediated magnetic coupling of ionic impurities, as required for a diluted magnetic semiconductor. In this thesis, this question will be answered for transition-metal implanted ZnO single crystals. Magnetic secondary phases, namely metallic Fe, Co and Ni nanocrystals, are formed inside ZnO. They are - although difficult to detect by common approaches of structural analysis - responsible for the observed ferromagnetism. Particularly Co and Ni nanocrystals are crystallographically oriented with respect to the ZnO matrix. Their structure phase transformation and corresponding evolution of magnetic properties upon annealing have been established. Finally, an approach, pre-annealing ZnO crystals at high temperature before implantation, has been demonstrated to sufficiently suppress the formation of metallic secondary phases.
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Gupta, Shalini. "Growth of novel wide bandgap room temperature ferromagnetic semiconductor for spintronic applications." Diss., Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/33809.

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This work presents the development of a GaN-based dilute magnetic semiconductor (DMS) by metal organic chemical vapor deposition (MOCVD) that is ferromagnetic at room temperature (RT), electrically conductive, and possesses magnetic properties that can be tuned by n- and p-doping. The transition metal series (TM: Cr, Mn, and Fe) along with the rare earth (RE) element, Gd, was investigated in this work as the magnetic ion source for the DMS. Single- phase and strain-free GaTMN films were obtained. Optical measurements revealed that Mn is a deep acceptor in GaN, while Hall measurements showed that these GaTMN films were semi-insulating, making carrier mediated exchange unlikely. Hysteresis curves were obtained for all the GaTMN films, and by analyzing the effect of n- and p-dopants on the magnetic properties of these films it was determined that the magnetization is due to magnetic clusters. These findings are supported by the investigation of the effect of TM dopants in GaN nanostructures which reveal that TMs enhance nucleation resulting in superparamagnetic nanostructures. Additionally, this work presents the first report on the development of GaGdN by MOCVD providing an alternate route to developing a RT DMS. Room temperature magnetization results revealed that the magnetization strength increases with Gd concentration and can be enhanced by n- and p-doping, with holes being more efficient at stabilizing the ferromagnetic signal. The GaGdN films obtained in this work are single-phase, unstrained, and conductive making them suitable for the development of multifunctional devices that integrate electrical, optical, and magnetic properties.
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Knapp, Alexander Gerhard [Verfasser], and J. [Gutachter] Geurts. "Resonant Spin Flip Raman-Spectroscopy of Electrons and Manganese-Ions in the n-doped Diluted Magnetic Semiconductor (Zn,Mn)Se:Cl / Alexander Gerhard Knapp ; Gutachter: J. Geurts." Würzburg : Universität Würzburg, 2019. http://d-nb.info/1193927218/34.

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Wang, Lei. "Exploratory synthesis and characterization of a new class of mixed-anion framework chalcohalides and oxyhalide and its potential applications for diluted magnetic semiconductors." Connect to this title online, 2007. http://etd.lib.clemson.edu/documents/1181668846/.

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Zeng, Li. "Disordered electronic and magnetic systems - transition metal (Mn) and rare earth (Gd) doped amorphous group IV semiconductors (C, Si, Ge)." Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2007. http://wwwlib.umi.com/cr/ucsd/fullcit?p3284117.

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Thesis (Ph. D.)--University of California, San Diego, 2007.
Title from first page of PDF file (viewed January 9, 2008). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 123-132).
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Kunets, Vasyl. "Micro Hall devices based on high electron velocity semiconductors." Doctoral thesis, [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=973088672.

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Marin, Ivan Silvestre Paganini. "Propriedades eletrônicas de heteroestruturas semicondutoras magnéticas diluídas." Universidade de São Paulo, 2007. http://www.teses.usp.br/teses/disponiveis/76/76132/tde-21082008-111614/.

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Neste trabalho e apresentado um estudo, via teoria de massa efetiva multibanda autoconsistente de heteroestruturas de semicondutores magnéticos diluídos, generalizada para incluir parâmetros de diferentes materiais. A interacao magnética e descrita por um modelo de campo médio baseado no mecanismo de troca indireta, com a possibilidade de inclusão de diferentes íons magnéticos. As equacoes de massa efetiva são resolvidas de forma autoconsistente com o auxílio da equacao de Poisson. As interacoes de spin-órbita e de troca-correlacao, na aproximacao de densidade local, são incluídas no cálculo. O método e aplicado para o estudo das estruturas de bandas e densidades de carga com separacao por spin do portador de heteroestruturas com dopagem tipo-n e tipo-p, variando a geometria dos pocos magnéticos e também o período da super-rede, as densidades de portadores e as concentracoes de íons magnéticos. Solucoes autoconsistentes da equacao de massa efetiva são encontradas para o oxido semicondutor (Zn,Co)O. Será mostrada a separacao de portadores por spin em funcao dos parâmetros variados, simulando diversas concentracoes possíveis, utilizadas em sistemas descritos na literatura, e será analisado o comportamento dos perfis de potencial. Usando os dados obtidos, um diagrama de fases será traçado com base na polarizacao total ou parcial dos portadores, e o seu comportamento será discutido. Também serão mostradas as estruturas de bandas, os perfis de potencial e as distribuicoes de carga do semicondutor (GaMn)As, variando as densidades de portadores e a direcao do campo magnético intrínseco, gerado pela dopagem com íons magnéticos. Os resultados obtidos neste trabalho podem servir de guia para futuras experiências e para o desenvolvimento de dispositivos com semicondutores magnéticos diluídos baseados em (Zn,Co)O e (Ga,Mn)As. Os métodos aqui descritos são gerais e podem ser utilizados para outros materiais.
This work presents a self-consistent multiband effective mass theory applied to diluted magnetic semiconductor heterostructures, generalized to include parameters of different ma- terials. The magnetic interaction is described by a mean-field approximation based on indirect- exchange mecanism, with the possibility of inclusion of different magnetic ions. The effective mass equations are solved self-consistently with the help of the Poisson equation. Spin-orbit and exchange-correlation interactions are included in the simulation in the local density appro- ximation. The method is used to study band structures and charge densities separated by spin in n- and p-type heterostructures. The magnetic well\'s geometry, the superlattice period, the carrier density and the magnetic ion concentration are changed. Self-consistent solutions of the effective mass equation are found for the semiconductor oxide (Zn,Co)O. Charge separation by spin will be show in function of the variation of the simulation parameters, simulating several ion concentrations and charge densities used in systems described in literature, and the potenti- als profiles will be analised. Using the data obtained a phase diagram will be plotted, based on the carrier total or partial carrier polarization, and a model for the behavior of the phase diagram will be discussed. It will also be shown band structures, potential profiles and charge densities of the (Ga,Mn)As semiconductor, varying it carrier density and the direction of the intrinsic magnetic field, generated by the magnetic ions that doped the heterostructure. The results ob- tained in this work can be used as a guide in future experiences and development of devices with diluted magnetic semiconductors based on (Zn,Co)O and (Ga,Mn)As. The methods here described are general and can be used for other materials.
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Mendes, Udson Cabral 1984. "Electronic and optical properties of diluted magnetic semiconductors quantum wells and quantum dots = Propriedades eletrônicas e ópticas de poços quânticos e pontos quânticos de semicondutores magnéticos diluídos." [s.n.], 2014. http://repositorio.unicamp.br/jspui/handle/REPOSIP/276958.

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Orientador: José Antônio Brum
Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin
Made available in DSpace on 2018-08-24T13:58:03Z (GMT). No. of bitstreams: 1 Mendes_UdsonCabral_D.pdf: 12052104 bytes, checksum: 67d2d70413e86cd914ef0145b639ff5b (MD5) Previous issue date: 2014
Resumo: Nesta tese, investigamos teoricamente as propriedades eletrônicas e ópticas de poços quânticos e pontos quânticos de semicondutores magnéticos diluídos. Este estudo é fortemente motivado por muitos resultados experimentais sobre as propriedades ópticas desse materiais. Usando a teoria do funcional da densidade dependente de spin descrevemos os estados eletrônicos como função do campo magnético externo para poços quânticos que possuem barreiras dopadas com impurezas magnéticas. Nosso modelo leva em conta os efeitos de muitos-corpos do gás de buracos e as interações entre portadores e os íons magnéticos. Comparamos nossos resultados com os dados experimentais disponíveis, que apresentam forte oscilações da luz polarizada circularmente como função do campo magnético. Nossos resultados apresentam excelente concordância qualitativa e quantitativa com os resultados experimentais. Mostramos que os efeitos de troca do gás de buraco são responsáveis pela forte oscilação observada na fotoluminescência. Também realizamos uma investigação sistemática dos parâmetros da heteroestrutura afim de aumentar a interação de troca entre portadores e íons de Mn. Com o nosso modelo entedemos os diferentes regimes de relaxação de spin do elétron em poços quânticos com barreiras dopadas com impurezas magnéticas. Nós também investigamos as propriedades eletrônicas e ópticas de pontos quânticos carregados dopados com uma única impureza magnética em seu centro. Usando métodos de diagonalização exata mostramos que os elétrons que não estão diretamente acoplados com o íon de Mn acoplam-se via uma interação indireta que é mediada pela interação elétron-elétron. Este acoplamento indireto entre elétrons e Mn pode ser tanto ferromagnético quanto antiferromagnético dependendo de ambos confinamento e número de camadas eletrônicas confinadas no ponto quântico. Demonstramos que este acoplamento indireto é um efeito importante mesmo quanto o íon de Mn não esta no centro do ponto quântico. O acoplamento indireto existe independentemente do tipo de interação direta entre portadores e a impureza magnética. Também extendemos a teoria de fotoluminescência para essa heteroestrutura. Observamos que a interação indireta entre portadores e íon magnético gera uma estrutura fina em ambos os estados iniciais e finais da emissão, o que nos permite determinar o número de camadas confinadas no ponto quântico e o spin eletrônico. Com esse método de diagonalização exata, explicamos a origem da estrutura fina do biexciton confinado em um ponto quântico dopado com uma única impureza magnética
Abstract: In this thesis, we theoretically investigate the electronic and optical properties of diluted magnetic semiconductors quantum wells and quantum dots. This is strongly motivated by many experimental results on the optical properties of these materials. Using spin-density functional theory we described the electronic states as a function of the external magnetic field for quantum wells which have barriers doped with magnetic impurities. Our model takes into account the many-body effects of the two-dimensional hole gas and the interaction between carriers and the magnetic ions. We compare our findings with the available experimental data, which shows strong oscillations in the circularly polarized light as a function of the magnetic field. Our results show excellent qualitative and quantitative agreement with the experimental data. We show that the hole gas exchange effects are responsible for the strong oscillations observed in the photoluminescence. We perform a systematic investigation of the heterostructure parameters in order to enhance the carriers-Mn exchange interaction. With our model we understand the different regime of the electron¿s spin relaxation in quantum wells with barriers doped with Mn impurities. We also investigate the electronic and optical properties of charged quantum dots doped with a single magnetic impurity in its center. Using an exact diagonalization method we show that the electrons that are not directly coupled with Mn do so via an indirect coupling mediated by electron-electron interaction. This indirect electron-Mn coupling can be either ferromagnetic or antiferromagnetic depending on both quantum dot confinement and the number of electronic confined shells. We also demonstrate that the indirect electron-Mn coupling is an important effect even when Mn is off-center. This coupling exists independently of the type of the direct interaction between carriers and Mn impurity. We also extend the theory of photoluminescence for charged quantum dots containing a single magnetic impurity. We show that the indirect interaction between carriers and magnetic ion generates a fine structure in both initial and final states of the emission, which allows us to determinate the number of confined shells in the quantum dots and the electronic spins. Whit this exact diagonalizationmethod, we explain the origin of the fine structure of a biexciton confined in quantum dot containing a single Mn impurity
Doutorado
Física
Doutor em Ciências
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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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