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Tesi sul tema "Resonant tunnelling in semiconductors"

Autore: Grafiati

Pubblicato: 4 giugno 2021

Ultima modifica: 16 febbraio 2022

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1

Rimmer, Nicholas. "Structure-property relationships in a resonant tunnelling diode." Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.308244.

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2

Hayden, Robin Kenneth. "High magnetic field studies of hole resonant tunnelling." Thesis, University of Nottingham, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334551.

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3

Goodings, Christopher John. "Variable-area resonant tunnelling diodes using implanted gates." Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.282159.

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4

Booker, Stuart Michael. "Theory of tunnelling in double barrier heterostructures." Thesis, University of Nottingham, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334465.

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5

Leadbeater, Mark Levence. "Resonant tunnelling in semiconductor heterostructures." Thesis, University of Nottingham, 1990. http://eprints.nottingham.ac.uk/28733/.

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This thesis examines the electrical transport properties of a series of n-type GaAs/(AIGa)As double barrier resonant tunnelling devices with well widths between 50 angstrem and 2400 angstrem . The current-voltage characteristics show peak-to-valley ratios as high as 25:1 and as many as seventy resonances, with clear evidence of quantum interference effects at room temperature. The application of a high magnetic field parallel to the current flow produces magnetooscillations in the transport properties which allow the sheet charge density in the accumulation layer to be determined. The energy level in the well over a wide range of bias is obtained from analysis of thermal activation of resonant tunnelling. The contributions of elastic scattering and LO phonon emission to the valley current are investigated spectroscopically with a magnetic field and two phonon modes of the (AIGa)As barrier are observed. The buildup of space charge in the quantum well at resonance leads to intrinsic bistability in the current and differential capacitance of an asymmetric structure. Magnetoquantum oscillations due to a degenerate electron gas in the well are used to measure this charge buildup and demonstrate that the tunnelling process is truly sequential. The bistability is dramatically enhanced at high magnetic fields when the lowest energy Landau level of the well can accommodate a high electron density. In a strongly asymmetric sample, a new kind of bistability is observed where the off-resonant current exceeds the resonant current due to enhancement of charge buildup by intersubband scattering. The modulation of the scattering rate by a magnetic field produces periodic oscillations in the width of the bistability. In a magnetic field applied perpendicular to the current, the resonances are broadened as a consequence of the conservation of canonical momentum. The transition from electric to magnetic quantisation in wide wells is investigated and tunnelling into interfacial Landau levels is observed. The angular dependence of the resonances is used to probe conduction band anisotropy. In a tilted field, a completely new type of magneto-oscillations is observed.

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6

Evans, Bryn. "Optical and magnetic studies of p-i-n resonant tunnelling devices." Thesis, University of Nottingham, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.307721.

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7

Kuznetsov, Vladimir. "Mesoscopic effects in conduction and noise of GaAs microstructures." Thesis, University of Exeter, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337746.

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8

Sakai, Joao Wesley Lopes. "Donor-assisted resonant tunnelling in semiconductor heterostructures." Thesis, University of Nottingham, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387861.

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9

Iredale, Nicholas Herbert. "Low-dimensional resonant tunnelling between coupled electron gases." Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.388434.

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10

Smith, Jason Michael. "Resonant tunnelling in GaAs / AlAs double barrier heterostructures under elevated hydrostatic pressure and in high magnetic fields." Thesis, University of Oxford, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337539.

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11

Alves, Elmo Salomao. "High magnetic field studies of resonant tunnelling and lateral superlattices." Thesis, University of Nottingham, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.280100.

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12

Conterio, Michael John. "An electrically driven resonant tunnelling semiconductor quantum dot single photon source." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708597.

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13

Honda, S., H. Itoh, J. Inoue, et al. "Spin polarization control through resonant states in an Fe/GaAs Schottky barrier." American Physical Society, 2008. http://hdl.handle.net/2237/11246.

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14

Tewordt, Matthias Ludwig. "Resonant tunnelling in quantum dots." Thesis, University of Cambridge, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.260415.

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15

Hutchinson, A. "Acoustoelectric interactions in resonant tunnelling structures." Thesis, University of Cambridge, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.604843.

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This thesis presents a novel device architecture allowing the monolithic integration of SAWs and semiconductors, which compensates for the inherent weakness of piezoelectric coupling in GaAs by relying on a strong non-local interaction mechanism. A special double-barrier quantum well RTS is designed so that large vertical currents can be sensitivity triggered by a small potential near the surface of the structure, such as the potential associated with a SAW. When a SAW beam is incident on the RTS mesa, the peaks ( and valleys) of the SAW electric field change the potential across the quantum well, resulting in local increases (and decreases) of the current through the structure. With the appropriate device design, the net effect of the SAW integrated over the entire RTS mesa will induce a microwave current in the receiving circuit connected to the RTS emitter. The basic linear and nonlinear properties of the microwave response have been investigated. Simple phenomenological models taking into account the spatial distribution of the SAW electric field and the nonlocality of the RTS conductivity have demonstrated good agreement with experimental results. The effect of varying the RTS layer structure on both the dc characteristics and the microwave response has been investigated theoretically, and experiments once again support the predictions. A process for non-annealed Ohmic contact to the RTS emitter has been optimized, in which Al is grown <I>in situ</I> on highly-doped GaAs incorporating several layers of <I>δ</I>-doping near the surface. The use of this contact method helps to eliminate the extrinsic instability observed in the negative differential resistance region of early devices. Finally, possible applications of the interaction are discussed, including a proposal for the parametric generation of very high frequency SAWs.

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16

McDonnell, Paul. "Resonant tunnelling across double barrier structures." Thesis, University of Nottingham, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.285640.

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17

Wilkinson, Paul Bryan. "Quantum chaos in resonant tunnelling diodes." Thesis, University of Nottingham, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.363557.

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18

Turner, Thomas Stephen. "Optical studies of resonant tunnelling structures." Thesis, University of Nottingham, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.284112.

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19

Figueiredo, José Maria Longras. "Optoelectronic properties of resonant tunnelling diodes." Tese, Universidade do Porto. Reitoria, 2000. http://hdl.handle.net/10216/14347.

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20

Razvan, Baba. "Resonant tunnelling diodes for THz communications." Thesis, University of Glasgow, 2018. http://theses.gla.ac.uk/30870/.

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Abstract (sommario):

Resonant tunnelling diodes realised in the InGaAs/AlAs compound semiconductor system lattice-matched to InP substrates represent one of the fastest electronic solid-state devices, with demonstrated oscillation capability in excess of 2 THz. Current state-of-the-art offers a poor DC-to-RF conversion efficiency. This thesis discusses the structural issues limiting the device performance and offers structural design optimums based on quantum transport modelling. These structures are viewed in the context of epitaxial growth limitations and their extrinsic oscillator performance. An advanced non-destructive characterisation scheme based on low-temperature photoluminescence spectroscopy and high-resolution TEM is proposed to verify the epitaxial perfection of the proposed structure, followed by recommendations to improve the statistical process control, and eventually yield of these very high-current density mesoscopic devices. This work concludes with an outward look towards other compound semiconductor systems, advanced layer structures, and antenna designs.

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21

Figueiredo, José Maria Longras. "Optoelectronic properties of resonant tunnelling diodes." Doctoral thesis, Universidade do Porto. Reitoria, 2000. http://hdl.handle.net/10216/14347.

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22

Martin, Patrick Michael. "Magnetospectroscopy of electron and hole tunnelling in (AlGa) as resonant tunnelling structures." Thesis, University of Nottingham, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.363614.

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23

Sellai, Azzouz. "Double barrier resonant tunnelling diodes and applications." Thesis, University of Nottingham, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334973.

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24

Thornton, Andrew Simon Graham. "Resonant tunnelling through zero dimensional quantum dots." Thesis, University of Nottingham, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.298032.

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25

Nemr, Noureddine I. "Resonant tunnelling nanostructures for THz energy harvesting." Thesis, University of Liverpool, 2018. http://livrepository.liverpool.ac.uk/3022929/.

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26

Jacobs, Kristof. "Development of resonant tunnelling diode terahertz emitter." Thesis, University of Sheffield, 2015. http://etheses.whiterose.ac.uk/9304/.

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This thesis reports on the development of high current density InGaAs/AlAs/InP resonant tunnelling diodes (RTDs) grown by metal-organic vapour phase epitaxy (MOVPE) for terahertz (THz) applications. A wide variety of characterisation techniques are employed to investigate the material properties and quality on the wafer level allowing future device and growth optimisation. An optical characterisation technique based on photoluminescence (PL) spectroscopy is developed to non-destructively map the doping and structural composition of the RTD on the wafer level. A new non-destructive optical characterisation technique to resolve the absolute energy level position of the first electron state of RTDs through low temperature PL spectroscopy is also reported. The absolute energy levels are resolved by a combination of type-I and type-II quantum well (QW) recombination, allowing an investigation into important scattering mechanisms affecting device performance, and monitor the QW alloy content and thickness non-destructively. Details of the growth process and the characterisation techniques are discussed. A new fabrication technique based on conventional i-line photolithography for micron scale high current density RTD devices is also developed with accurate control over the final device area (and hence characteristics). This is achieved by measuring the V-I characteristic of the RTD during the fabrication process, which has not been previously possible. This was made possible by guiding the emitter current through the full RTD structure by a large second contact electrode on the collector side and using an air-bridge contact to the collector. Important information about the RTD performance is extracted by using this method. Temperature dependent V-I characterisation is also carried out to investigate the valley current of the RTD. Details of the design, fabrication, and characterisation of a room temperature operating THz emitter in the 300 GHz band are reported.

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27

Harrison, Paul Anthony. "Resonant tunnelling and luminescence in coupled quantum wells." Thesis, University of Nottingham, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.363933.

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28

Holder, Jonathan Paul. "Resonant tunnelling spectroscopy of vertical GaAs/AlGaAs structures." Thesis, University of Exeter, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.312281.

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29

Quierin, Marcus Alfred. "Gated resonant tunnelling diodes fabricated by MBE regrowth." Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627241.

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30

Billen, Keri. "Ion implantation of double-barrier resonant-tunnelling diodes." Thesis, University of Surrey, 1996. http://epubs.surrey.ac.uk/843881/.

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Many doses of ions have been implanted through near-surface AlGaAs/GaAs double-barrier diodes. The first objective of this work was the creation of a resistive layer beneath the diodes in selected areas of the wafer. It is shown that if the damage within the double-barrier diodes could be annealed without removing the resistive layer, the three-dimensional integration of the diodes with a second level of devices beneath the resistive layer could be attained. Implantation-and-annealing to create either a damaged or a chemically-compensated resistive layer has been attempted, where, during both types of process, the damage within the doublebarrier diodes was much less than that below them. After implantation of 5.0x1018 2.0MeV B+ ions cm-2, and anneals at 600° C, near-surface Al0.4Ga0.6As/GaAs double-barrier diodes still had good quality negative differential-resistance. It is shown that if (the smaller and less damaging) 1.2MeV Be+ ions were implanted instead of the 2.0MeV B+ ions, an n+-doped layer beneath the diodes can, in principle, be chemically compensated without destroying the diodes irreparably. This work was the first to successfully carry out the anneal-induced recovery of an ion-implanted electronic device having quantum-length-scale layers. The second objective of this work was the elucidation of the electronic and structural characteristics of the same implanted-and-annealed double-barrier diodes. Before annealing, electron conduction through the ion-implanted diodes was limited primarily by field-enhanced emission of electrons from defect states within the lightly-doped spacer layers. The current of ballistic electrons through the as-grown double-barrier structures was suppressed by implantation-and-annealing; this was probably caused by scattering of these electrons by the remaining defect states. The suppression of the ballistic-electron current within implanted-and- annealed double-barrier diodes is proposed to be the primary cause of their larger-than-as-grown 5K and 77K peak-to-valley current ratios. Multi-stage annealing of defects within the double-barrier diodes has been investigated by electrical measurements. The anneal-induced creation of defect clusters within the device mesas was confirmed by both DC and AC measurements, where these clusters were surrounded by percolation paths of as-grown material. Single-electron switching and resonant tunnelling through donor states have been observed within the percolation paths at 4.2K; these observations indicate that the typical diameter of the paths was probably less than five microns, and possibly less than one micron.

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31

Allford, Craig. "Resonant tunnelling in GaAs/AlGaAs triple barrier heterostructures." Thesis, Cardiff University, 2016. http://orca.cf.ac.uk/91151/.

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This thesis describes experimental and theoretical research into triple barrier resonant tunnelling structures which are attractive as potential high frequency oscillators in the terahertz frequency range. A lack of practical and coherent radiation emitters in this frequency range has resulted in it being named the \terahertz gap". However resonant tunnelling structures are seen as potential sources for practical solid state emitters which operate in this frequency range at room temperature. A series of symmetric and asymmetric GaAs/Al0:33Ga0:67As triple barrier resonant tunnelling structures have been studied at low temperatures to investigate the tunnelling electrical behaviour and origin of the current resonances observed in the current-voltage characteristics of these structures. The e�ect of charge accumulation in the emitter quantum well has been investigated, and has been found to signi�cantly alter the behaviour of the electrical characteristics of the structures. These investigations have provided a thorough understanding of the behaviour of these structures and has allowed for optimisation of the triple barrier design with a view to being utilised as a high frequency emitter. The current-voltage characteristics have also been studied as a function of temperature and a novel temperature dependent resonant tunnelling mechanism has been observed. The magnitude of the observed current resonance, which is associated with the energetic alignment to the n = 1 quasi-bound subband states increases with increasing sample temperature which is rare behaviour in systems dominated by quantum mechanics. Finally, the maximum oscillation frequency and output power of these resonant tunnelling structures has been calculated and an optimised triple barrier structure in which charge accumulation in the emitter quantum well does not occur has been designed. Simulated current-voltage characteristics for this design shows it improves the maximum oscillation frequency and maximum output power reported in current state of the art double barrier resonant oscillator structures.

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32

Gaskell, J. "High-frequency oscillations in graphene resonant tunnelling heterostructures." Thesis, University of Nottingham, 2016. http://eprints.nottingham.ac.uk/33694/.

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In this thesis, the form of the current-voltage characteristics and the resulting current oscillations in graphene-hexagonal boron nitride heterostructures are explored by means of theoretical investigation and are supported by experimental observations. The conditions for resonant tunnelling and the effect of device and circuit parameters are examined through simulation of the charge dynamics using the Bardeen Transfer Hamiltonian method. Studies of the effect of induced moir\'e patterns between the crystallographically aligned graphene and the boron nitride lattices are also undertaken, with recommendations for future investigation. It is theoretically shown that samples containing two layers of graphene, separated by hexagonal boron nitride tunnel barriers, produced higher frequency oscillations when the graphene lattices are aligned. This was found to be due to the decrease in wavefunction overlap in the misaligned samples, which is not compensated by the higher density of states available for tunnelling. Chemical doping of the graphene layers are also found to increase the frequency, as it allows the Dirac cones to be brought into alignment for resonant tunnelling with a higher number of states available. It is known that the mismatch in lattice constant between the graphene lattice and the hexagonal boron nitride lattice creates a moir\'e pattern. This, in turn, induces additional Dirac points in the band structure and thus leads to new features in the current-voltage characteristics. The theoretical simulations presented in this thesis are substantiated by recently-published experimental results, and provide insight into possible future high-frequency, room-temperature solid state oscillators and amplifiers. In conclusion, the mechanisms for resonant tunnelling in multiple graphene heterostructures are identified and demonstrated in this work, and provide promising evidence for novel high frequency technologies and further research.

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33

Mayne, A. J. "Scanning tunnelling microscopy of small adsorbates on semiconductors." Thesis, University of Oxford, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386614.

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34

Reker, Tobias. "Resonant magneto-tunnelling in GaAs/AlGaAs double-barrier heterostructures." Thesis, University of Oxford, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.393758.

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35

Zuo, Dingli. "Manufacturability of circuits based on resonant (interband) tunnelling diodes." Thesis, University of Cambridge, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648793.

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36

Hees, Simon Söhnke. "Single photon detection using quantum dot resonant tunnelling diodes." Thesis, University of Cambridge, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.613151.

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37

See, Un Siong Patrick. "In-situ focused ion beam patterned resonant tunnelling diodes." Thesis, University of Cambridge, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.624475.

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38

Peck, Andrew John. "Lateral tunnelling in two-dimensional electron systems." Thesis, University of Bath, 1994. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.385345.

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39

Kulikowski, Anoushka. "Phonon studies of energy loss in vertical tunnelling structures." Thesis, Lancaster University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.286990.

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40

Isic, Goran. "Electron transport in resonant tunnelling structures with spin-orbit interaction." Thesis, University of Leeds, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.545696.

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41

Steenson, David Paul. "The high-frequency application of double-barrier resonant tunnelling diodes." Thesis, University of Nottingham, 1993. http://eprints.nottingham.ac.uk/13957/.

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The aim of this Thesis was to try to develop an understanding of the growth and fabrication of Double Barrier Resonant Tunnelling (DBRT) diodes, in order to enhance their properties at millimetre wave frequencies (ie. above 35GHz). Chapter 1 introduces the DBRT diode and outlines some of its applications while Chapter 2 describes aspects of device fabrication. Chapter 3 discusses the solid-state and quantum mechanical aspects which determine the DBRT's current-voltage characteristics and Chapter 4 describes an extensive parametric study relating the device properties to the high frequency behaviour. Chapter 5 covers the applications of DBRT devices at high frequencies and presents some of the results achieved so far. Besides the primary objective of studying the properties which determine the high frequency application of DBRT devices (via. the characterization of an extensive range of structures grown for the project), the other goal was to try to improve upon the results of other workers in terms of generating power and to improve the efficiency of up and down conversion at millimetre wave frequencies. Perhaps the most promising application of DBRT devices is as self-oscillating mixers (SOM) which can also provide conversion gain (due to the wide bandwidth of the negative differential resistance) at the intermediate frequency. This is of great importance since it negates the need to generate a local oscillator signal and dispenses with complicated image rejection mixer arrangements (for superheterodyne mixing) and amplification stages, which are very difficult to build and are expensive at millimetre wave frequencies. Whilst working in collaboration with staff at the University of Leeds, department of Electronic and Electrical Engineering a SOM was fabricated on microstrip which gave a modest gain at around 10GHz. Similarly a DBRT diode was operated in waveguide at 106GHz and provided -9.8dBm of power as measured on a spectrum analyzer. Both of these results represent (to the authors knowledge) the best results currently seen for DBRT devices in the UK and Europe.

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42

Mansouri, Lamia. "Optical and high magnetic field studies of resonant tunnelling diodes." Thesis, University of Nottingham, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.338438.

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43

Nield, Stuart Alan. "Coulomb drag and resonant tunnelling between low-dimensional electron systems." Thesis, University of Cambridge, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.621296.

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44

Sammut, Carmel Victor. "An investigation of the microwave properties of resonant tunnelling devices." Thesis, University of Bath, 1992. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.306813.

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45

Kardynal, Beata Ewa. "Fabrication and physics of equilibrium electron tunnelling devices." Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.243018.

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46

Slight, Thomas James. "Integration of a resonant tunnelling diode and an optical communications laser." Thesis, University of Glasgow, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.433193.

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47

Elsaadi, Mussa Farag Mussa. "Resonant tunnelling diodes for millimetre and sub-millimetre wave mixing applications." Thesis, University of Leeds, 2016. http://etheses.whiterose.ac.uk/14367/.

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The primary intention of this research work was to evaluate a topology for a sub-harmonic down conversion mixer exploiting the fourth harmonic of a LO signal. Designs were evaluated by simulation at 640GHz and 320GHz with the aim of exploring the potential of a RTD based down-converter at 640GHz, in the 580-750GHz atmospheric window, with an intermediate frequency signal in the range around 2GHz by mixing with the fourth harmonic of a 159.5GHz LO signal. Related design studies were undertaken at 320GHz which gave a simulated single side band (SSB) conversion loss of 5.7dB, and with a LO power requirement of less than -9.5dBm which vindicated the principle, as far as the design stage is concerned, of using RTDs as the non-linear mixing element, where the layer design can be tailored to favour very low pump powers. The other, related, target of the current PhD work was to also explore the potential for high LO drive level mixers and their up-conversion efficiencies using the same novel devices, i.e. RTDs, but with a different layer design, better suited to support high pump powers in this instance. For achieving the latter goal, two different sub-harmonic up-conversion mixers employing a single RTD and using the second harmonic of an LO signal were designed and evaluated at two different frequencies. The first mixer design was aimed at 180 GHz providing -7.5dBm of output power while the second one should work at 110GHz showing output power in the range of -4dBm, and was used to initially evaluate the approach and which could, in principle, be later fabricated and measured. All these down and up-conversion mixers were carefully designed using ADS and HFSS and evaluated using two different technologies, microstrip and Grounded Coplanar Waveguide (GCPW), and both compared with a nearest Schottky diode based approaches, and also their physical mask was produced in anticipation of a later fabrication stage.

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48

Somma, Carmine. "Coherent Multidimensional Off-resonant THz Spectroscopy on Semiconductors." Doctoral thesis, Humboldt-Universität zu Berlin, 2017. http://dx.doi.org/10.18452/18512.

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Zum ersten Mal konnte die kohärente Erzeugung von ultrakurzen Pulsen mit Feld stärken im MV/cm Bereich mit einem Spektralbereich von 0.1-30 THz im organischen Kristall DSTMS. Kohärente mehrdimensionale Terahertzspektroskopie (CMTS) hat sich zu einer wichtigen Methode zur Untersuchung der niederenergetischen Anregungen von Halbleitern and deren kohärenter Dynamik entwickelt. Eine neuartige CMTS Methode mit drei phasenstarren, zueinander zeitverzögerten Terahertzpulsen wurde entwickelt. Sie beruht auf der kollinearen Wechselwirkung der Pulse mit der Probe, sodass verschiedene Ordnungen des nichtlinearen Signals in gleicher Richtung emittiert werden und deshalb gleichzeitig gemessen werden können. Amplitude und Phase des nichtlinearen Signals können durch elektro-optisches Abtasten vermessen werden, wodurch die zeitliche Entwicklung der kohärenten Wechselwirkungen in Echtzeit untersucht werden kann. CMTS erlaubt zusätzlich die eindeutige Zerlegung des nichtlinearen Signals in die verschiedenen nichtlinearen Ordnungen in der jeweiligen mehrdimensionalen Frequenzdomäne. Die nichtlineare, nicht-resonante Antwort zweier undotierter Halbleiter, des Ferroelektrikums Lithiumniobat (LiNbO3) und Indiumantimonids (InSb) kann mit dieser neuartigen Methode untersucht werden. In LiNbO3 wird das nichtlineare Signal durch einen Femtosekunden nichtlinearen Verschiebestrom (SC) hervorgerufen. SC wird durch die gebrochene Inversionssymmetrie des Kristalls in Verbindung mit einer ultraschnellen Dephasierung der feldinduzierten, kohärenten interband-Polarisation hervorgerufen. Die Dephasierung der interband-Polarisation erlaubt das Tunneln von Elektronen vom Valenzband in das Leitungsband. In InSb wird das kohärente Signal durch sowohl zwei-Phonen als auch zwei-Photonen interband-Anregungen erzeugt. Die impulsive Anregung einer kohärenten zwei-Phononen Polarisation wird durch das große Übergangsdipolmoment von InSb verstärkt, was zu deutlich größeren Amplituden der Polarisation als im linearem Regime führt.<br>For the first time, the coherent generation of ultrashort MV/cm field pulses with a spectrum covering the frequency range 0.1-30 THz is demonstrated in the organic crystal DSTMS. Coherent multidimensional terahertz spectroscopy (CMTS) has become a prominent technique for, e.g., driving low-energy excitations in semiconductors and monitoring their coherent dynamics. A novel CMTS technique using three phase-locked inter-delayed THz pulses is implemented. It relies on a collinear interaction of the pulses with a sample, so that different contributions to the nonlinear signal are emitted in the same direction, and thus can be measured all at once. Phase-resolved detection by electro-optic sampling allows for measuring amplitude and absolute phase of the nonlinear signal, thereby enabling to investigate the evolution of coherent interactions between quantum excitations in real time. In CMTS, the nonlinear signal is dissected into the distinct nonlinear contributions in the corresponding multidimensional frequency domain. This novel technique is applied to study the nonlinear off-resonant response of two undoped bulk semiconductors, the wide-bandgap ferroelectric lithium niobate (LiNbO3) and the narrow-bandgap indium antimonide (InSb). In LiNbO3, the nonlinear signal is generated by a femtosecond nonlinear shift current (SC), a distinctive characteristic of the bulk photovoltaic effect. The SC stems from the lack of inversion symmetry and the ultrafast dephasing of the field-induced interband coherent polarization due to a sufficiently high decoherence rate, which enables tunneling of electrons from the valence to the conduction band. In InSb, the nonlinear signal is caused by the coherent response on both the two-phonon and two-photon interband excitations. The impulsive generation of the two-phonon coherent polarization is enhanced by the large interband transition dipole of InSb, resulting in much larger polarization amplitudes than in the regime of linear response.

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49

Wang, Liquan. "Reliable design of tunnel diode and resonant tunnelling diode based microwave sources." Thesis, University of Glasgow, 2012. http://theses.gla.ac.uk/3423/.

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This thesis describes the reliable design of tunnel diode and resonant tunneling diode (RTD) oscillator circuits. The challenges of designing with tunnel diodes and RTDs are explained and new design approaches discussed. The challenges include eliminating DC instability, which often manifests itself as low frequency parasitic oscillations, and increasing the low output power of the oscillator circuits. To stabilise tunnelling devices, a common but sometimes ineffective approach is the use of a resistor of suitable value connected across the device. It is shown in this thesis that this resistor tunnel diode circuit can be described by the Van der Pol model. Based on this model, design equations have been derived which enable the design of current-voltage (I-V) measurement circuits that are free from both low frequency bias oscillations and high frequency parasitic oscillations. In the conventional setup, the I-V characteristic of the tunnelling device is extracted from the measurement by subtracting from the measured current the current through the stabilising resistance at each bias voltage. In this thesis, also using the Van der Pol model, a circuit for the direct measurement of I-V characteristics is proposed. This circuit utilises a series resistor-capacitor combination in parallel with the tunnelling device for stabilisation. Experimental results show that IV characterisation of tunnel diodes in the negative differential resistance (NDR) region free from oscillations can be made. A new test set-up suitable for radio frequency (RF) characterisation of tunnel diodes over the entire NDR region was also developed. Initial measurement results on a packaged tunnel diode indicate that accurate characterisation and subsequent small-signal equivalent circuit model extraction for the NDR region can be done. To address the limitations of low output power of tunnel diode or RTD oscillators, a new multiple device circuit topology, incorporating a novel design methodology for the DC bias decoupling circuit, has been developed. It is based on designing the oscillator specifically for sinusoidal oscillations, and not relaxation oscillations which are also possible in tunnel diode oscillators. The oscillator circuit can also be described by the Van der Pol model which provides theoretical predictions of the maximum inductance, in terms of the tunnel diode device parameters, that is required to resonate with the device capacitance for sinusoidal oscillations. Each of the tunnel diodes in the multiple device oscillator circuit is decoupled from the others at DC and so can be stabilised independently. The oscillator topology uses parallel resonance but with each tunnel diode individually biased and DC decoupled making it possible to employ several tunnel diodes for higher output power. This approach is expected to eliminate parasitic bias oscillations in tunnel diode oscillators whilst increasing the output power of a single oscillator. Simulation and experimental oscillator results were in good agreement, with a two-tunnel diode oscillator exhibiting approximately double the output power as compared to that of a single tunnel diode oscillator, i.e. 3 dB higher. Another method considered for the realisation of higher output power tunnel diode or RTD oscillators was series integration of the NDR devices. A new method to suppress DC instability of the NDR devices connected in series with all the devices biased in their NDR regions was investigated. It was successfully employed for DC characterisation with integrations of 2 and 5 tunnel diodes. Even though no suitable oscillator circuit topology and/or methodology with series-connected NDR devices could be established for single frequency oscillation, the achieved results indicated that this approach may be worthy of further investigation. The final aspect of this project focussed on the monolithic realisation of RTD oscillators. Monolithic oscillators in coplanar waveguide (CPW) technology were successfully fabricated and worked at a fundamental frequency of 17.5 GHz with -21.83 dBm output power. Finally, to assess the potential of RTD oscillators for high frequency signal generation, a theoretical analysis of output power of stabilised RTD oscillators was undertaken. This analysis suggests that it may be possible to realise RTD oscillators with high output power (0 dBm) at millimetre-wave and low terahertz (up to 1 THz) frequencies.

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50

Roschke, Matthias Carleton University Dissertation Engineering Electronics. "A study of resonant tunnelling diodes and their application to hybrid oscillators." Ottawa, 1995.

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