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Hong, Sang Jeen. "Real-time malfunction diagnosis and prognosis of reactive ion etching using neural networks." Diss., Available online, Georgia Institute of Technology, 2004:, 2003. http://etd.gatech.edu/theses/available/etd-04082004-180227/unrestricted/hong%5Fsang%5Fj%5F200312%5Fphd.pdf.
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Wasenczuk, Adam. "Defects in epitaxial II-VI semiconductors." Thesis, University of Southampton, 1998. https://eprints.soton.ac.uk/426603/.
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Cobden, David Henry. "Individual defects in mesoscopic transistors." Thesis, University of Cambridge, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386908.
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Gladney, Dewey Clinton. "Simulating radiation-induced defects on semiconductor devices." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Sep%5FGladney.pdf.
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Doolittle, William Alan. "Fundamental understanding, characterization, passivation and gettering of electrically active defects in silicon." Diss., Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/15710.
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Gatti, Fabio Garcia. "Uma contribuição para caracterização de níveis de energia de impurezas em AlxGa1-xAs tipo n." Universidade de São Paulo, 2000. http://www.teses.usp.br/teses/disponiveis/76/76132/tde-05052010-153410/.
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Neste trabalho apresentamos medidas de fotocondutividade, decaimento da fotocondutividade persistente, resistência em função da temperatura em amostras de AlxGa1-xAs de gap direto e indireto, dopadas com Si. Comparamos as teorias de Brooks-Herring e Takimoto, ambas referentes ao espalhamento por impurezas ionizadas, e sua aplicabilidade para nosso material. Interpretamos a presença de um estado de energia intermediário nos cálculos da energia de ativação baseado nos resultados de concentração de elétrons livres em função da temperatura .como devido ao defeito D-. Nos resultados de decaimento da fotocondutividade persistente no intervalo de 80 - 100K, contamos com a contribuição do espalhamento por dipolos e propomos o par d+ - VAS- como os responsáveis pela formação destes dipolos e conseqüente melhoria do ajuste da simulação numérica.In this work, we show results of photoconductivity, decay of persistent photoconductivity, resistance x temperature in Si doped direct and indirect bandgap AlxGa1-xAs. We compare Brooks-Herring and Takimoto theories, both in reference to ionized impurity scattering applied to our material. We interpret the intermediate state in our calculation of activation energy as a D- defect. In the numerical simulation of decay of persistent photoconductivity in the range 80-100 K, we propose the dipole pair d+ - VAS- responsible for the fitting improvement, when the dipole scattering is taken into account.
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Höglund, Andreas. "Electronic Structure Calculations of Point Defects in Semiconductors." Doctoral thesis, Uppsala universitet, Fysiska institutionen, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-7926.
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In this thesis point defects in semiconductors are studied by electronic structure calculations. Results are presented for the stability and equilibrium concentrations of native defects in GaP, InP, InAs, and InSb, for the entire range of doping conditions and stoichiometry. The native defects are also studied on the (110) surfaces of InP, InAs, and InSb. Comparing the relative stability at the surface and in the bulk, it is concluded that the defects have a tendency to migrate to the surface. It is found that the cation vacancy is not stable, but decomposes into an anion antisite-anion vacancy complex. The surface charge accumulation in InAs is explained by complementary intrinsic doping by native defects and extrinsic doping by residual hydrogen. A technical investigation of the supercell treatment of defects is performed, testing existing correction schemes and suggesting a more reliable alternative. It is shown that the defect level of [2VCu-IIICu] in the solarcell-material CuIn1-xGaxSe2 leads to a smaller band gap of the ordered defect γ-phase, which possibly explains why the maximal efficiency for CuIn1-xGaxSe2 has been found for x=0.3 and not for x=0.6, as expected from the band gap of the α-phase. It is found that Zn diffuses via the kick-out mechanism in InP and GaP with activation energies of 1.60 eV and 2.49 eV, respectively. Explanations are found for the tendency of Zn to accumulate at pn-junctions in InP and to why a relatively low fraction of Zn is found on substitutional sites in InP. Finally, it is shown that the equilibrium solubility of dopants in semiconductors can be increased significantly by strategic alloying. This is shown to be due to the local stress in the material, and the solubility in an alloy can in fact be much higher than in either of the constituting elements. The equilibrium solubility of Zn in Ga0.9In0.1P is for example five orders of magnitude larger than in GaP or InP.
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Höglund, Andreas. "Electronic structure calculations of point defects in semiconductors /." Uppsala : Acta Universitatis Upsaliensis, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-7926.
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Goss, Jonathan Paul. "A first principles study of defects in semiconductors." Thesis, University of Exeter, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.361336.
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Ewels, Christopher Paul. "Density functional modelling of point defects in semiconductors." Thesis, University of Exeter, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.388588.
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Eberlein, Thomas Andreas Georg. "Point and extended defects in Group IV semiconductors." Thesis, University of Exeter, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.398963.
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Elsherif, Osama S. "Electrical characterisation of defects in wide bandgap semiconductors." Thesis, Sheffield Hallam University, 2012. http://shura.shu.ac.uk/19622/.
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Defects usually have a very large influence on the semiconductor material properties and hence on fabricated electronic devices. The nature and properties of defects in semiconducting materials can be investigated by applying electrical characterization techniques such as thermal admittance spectroscopy (TAS), deep level transient spectroscopy (DLTS) and high resolution Laplace-DLTS measurements. This dissertation presents the electrical characterisation of two different wide bandgap semiconducting materials (polycrystalline diamond and GaN) which have both recently attracted a great deal of attention because of their potential applications in the fields of power electronics and optoelectronics. Raman spectroscopy, I-V and C-V measurements were carried out as supporting experiments for the above investigations. The first part of this work focuses on studying the effect of B concentration on the electronic states in polycrystalline diamond thin films grown on silicon by the hot filament chemical vapour deposition method. A combination of high-resolution LDLTS and direct-capture cross-section measurements was used to investigate whether the deep electronic states present in the layers originated from point or extended defects. There was good agreement between data on deep electronic levels obtained from DLTS and TAS experiments. A number of hole traps have been detected; the majority of these levels show an unusual dependence of the DLTS signal on the fill pulse duration which is interpreted as possibly the levels are part of extended defects within the grain boundaries. In contrast, a defect level found in a more highly doped film, with an activation energy of -0.37 eV, exhibited behaviour characteristic of an isolated point defect, which we attribute to B-related centres in the bulk diamond, away from the dislocations. The second part of this thesis presents electrical measurements carried out at temperatures up to 450 K in order to study the electronic states associated with Mg in Mg-doped GaN films grown on sapphire by metalorganic vapour phase epitaxy, and to determine how these are affected by the threading dislocation density (TDD). Two different buffer layer schemes between the film and the sapphire substrate were used, giving rise to different TDDs in the GaN. Admittance spectroscopy of the films finds a single impurity-related acceptor level. It is observed in theses experiments that admittance spectroscopy detects no traps that can be attributed to extended defects, despite the fact that the dislocations are well-known to be active recombination centres. This unexpected finding is discussed in detail.
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Almrabet, Meftah M. "Electrically active defects in novel Group IV semiconductors." Thesis, Sheffield Hallam University, 2006. http://shura.shu.ac.uk/19253/.
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This thesis presents the electrical characterisation of defects in novel group IV semiconducting materials: semiconducting diamond and silicon germanium (SiGe) virtual substrates. Several methods to clean diamond surfaces are introduced, which lead to the fabrication of a diamond Schottky diode with acceptable characteristics. Current-Voltage (I-V) and Capacitance-Voltage (C-V) measurements were carried out to study the electrical properties of both the diamond and SiGe Schottky diodes. Deep level transient spectroscopy (DLTS) and Laplace DLTS were then carried out to investigate the deep electronic states in these devices. Scanning Electron Microscopy (SEM) was also used to investigate defects in the diamond samples. For the diamond Schottky diodes, I-V and C-V measurements confirmed the quality of the fabricated Schottky diode; the measured phase angle between capacitance and voltage was close to 90° for temperatures greater than 300K and frequencies above 200 kHz and the device clearly exhibited rectification. DLTS and LDLTS measurements of the diamond did not show any signatures that could be attributed to isolated point defects. This could be due to the fact that it was necessary to take the samples to higher temperatures in order to fully ionize the boron in the sample. The boron acceptor is at 0.37 eV above the valence band and therefore only about 5% is ionised at room temperature. During the major part of the study at Manchester, there was no access to a high temperature cryostat. However, a clear capacitance transient was observed at lower temperatures and it is proposed that this is due to emission of holes from boron. Deep traps will be located deeper in the band gap than the boron. An additional problem was that the sample was of polycrystalline structure and is full of grain boundaries, which appear to be implicated in the leakage currents present in our devices. I-V, C-V, DLTS and LDLTS were also used to investigate the deep states in the SiGe virtual substrate. I-V and C-V measurements showed that the SiGe Schottky diode showed some leakage (reported by the suppliers) but nevertheless the diode exhibited rectification. Analysis of the DLTS data showed the presence of a defect in the SiGe samples which could be a structural defect, probably dislocation-related. However, the low background doping meant that a considerable depth below the surface was being measured in DLTS and depth profiling was not possible.
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Bertram, Uwe Christoph. "Theoretical studies of Cs impurities in semiconductors." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319587.
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Claybourn, M. "Transient spectroscopy of II-VI semiconductors." Thesis, Durham University, 1985. http://etheses.dur.ac.uk/9298/.
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DLTS, ODLTS and DLOS have been used to characterise the main deep level trapping centres in some II-VI semiconductors; these were single crystal CdS, (ZnCd)S, CdSe, CdTe and ZnS, and polycrystalline CdS films. Undoped, single crystal CdS contained four electron traps as detected by DLTS, at 0.29eV, 0.41eV, 0.61eV and 0.74eV below the conduction band (CB). The first two were observed in all samples and were due to native defects. The two states of highest energy were found only in material that had been annealed in S or Cd vapours. The 0.61ev level could be photoinduced by illumination at photon energies greater than about 1eV. It decayed in the dark with an activation energy of 0.25eV. The 0.61eV and 0.74eV centres were associated with electrically active extended defects (subgrain boundaries Such samples had dislocation densities of about 10(^10) cm(^-2). Copper was found to be a residual impurity in CdS. It produced two deep hole traps resulting from a crystal field splitting of the Cu d(^9) state. They were detected by ODLTS and DLOS and were found at 0.35eV and 1.lev above the valence band (VB).Introduction of the isoelectronic impurity tellurium into CdS induced a hole repulsive centre at 0.21eV above the VB. This is thought to be an inportant radiative recombination centre. The main electron trap in CdS at 0.41eV was found to shift to higher energy with incorporation of Zn. Replacement of 20% of the Cd with Zn shifted the energy to 0.63eV. The level appeared fixed to the VB and had a similar functional dependence on composition as the band gap. The activation energies of the copper centres observed in CdS remained unchanged with incorporation of Zn up to the composition (^Zn)0.45 (^cd)0.55(^s) showed that the crystal field splitting was constant and that these levels were also pinned to the VB. During the fabrication process of the (ZnCd)S/Cu(_2)S solar cell, a deep level was induced at about 1.2eV below the CB. This is thought to be a recombination centre and one of the contributory factors to the reduction observed in the current collection efficiency of these devices. Polycrystalline CdS films were prepared by silk screen printing (SP) and evaporation. The SP films were annealed at various times and temperatures to improve the crystallinity of the layers. At 640C for 1hr, deep states at 0.16eV and 0.48eV were detected. The levels disappeared when annealed at 670C-700C and a new level was observed at 0.13eV. CdS/Cu(_2)S heterojunctions were prepared on the material sintered at 670C; this induced a further trapping level at 1.1eV and one that was poorly resolved. Copper diffused into the CdS during the fabrication of the device so the states associated with copper were detected at 0.35eV and 1.1eV, The evaporated CdS layers showed that the defect signature was sensitive to the type of substrate. Using Ag instead of the usual SnO(_x), deep states were induced at 0.48eV and 0.98eV below the CB. These Ag-associated impurity centres prevent the indiffusion of Cu during the optimising heat treatment of the CdS/Cu(_2)S heterojunction. This maintains the stoichicmetry of the Cu(_2)S layer, thereby, preventing degradation of the devices. CdSe and copper doped CdSe were found to contain several important defect centres: a native sensitising centre (0.64eV from the VB), a class I recombination centre (0.9eV from the CB), a copper impurity centre (0.2eV from the CB) and two native defects (0.16eVand 0.45eV from the CB). n-type CdTe grown by the Piper-Polich technique contained6 electron traps at 0.15eV, 0.21eV, 0.40eV, 0.47eV, 0.53eV and 0.63eV. Their presence was shown to be dependent upon the method of growth of the crystal by comparing with material grown by other techniques. One or more of these states were thought to be due to extended defects or Te precipitates. Low resistivity ZnS contained two deep electron traps at 0.25eV and O.50eV as detected by DLTS. In addition DLOS showed the presence of four further states at 1.25eV, 1.37eV, 1.89eV and 2.19eV below the CB. The first two are thought to be the strong luminescence centres observed by other workers.
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Lui, Mei-ki Pattie. "Acceptor defects in P-type gallium antimonide materials." Click to view the E-thesis via HKUTO, 2005. http://sunzi.lib.hku.hk/hkuto/record/B31648368.
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Or, Chun-tat. "Optical characterization of defects in GaN /." Hong Kong : University of Hong Kong, 2001. http://sunzi.lib.hku.hk/hkuto/record.jsp?B23768770.
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Sitch, Paul Kirst. "Ab-initio calculations of dislocation related properties in semiconductors." Thesis, University of Exeter, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240399.
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Lui, Mei-ki Pattie, and 雷美琪. "Acceptor defects in P-type gallium antimonide materials." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2005. http://hub.hku.hk/bib/B31648368.
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Port, Ruth Isabel. "Structural defects in MOVPE grown CdTe/GaAs." Thesis, Durham University, 1995. http://etheses.dur.ac.uk/5476/.
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This work presents a study of the character and distribution of structural defects in (00l)CdTe buffer layers grown on GaAs substrates by metal organic vapour phase epitaxy (MOVPE). These are of importance as hybrid substrates for the growth of Cd(_x)Hg(1-x)Te (CMT), a prominent infrared detector material. The 14.5% mismatch between CdTe and GaAs leads to a high-density of dislocations at the CdTe/GaAs interface, and threading through the layer. The presence of linear and planar defects is detrimental to the performance of CMT devices and it is desirable to reduce the density of dislocations to below l0(^5)cm(^-2). Results of high resolution X-ray diffraction (HRXRD) studies on a series of MOVPE grown CdTe/GaAs epilayers of different thickness and on a single thick layer which was repeatedly etched and remeasured are reported. Threading dislocation density was estimated from HRXRD full width at half maximum (FWHM) using a relationship proposed by Gay, Hirsch and Kelly and was found to decrease rapidly in the initial stages of layer growth. An optimum buffer layer thickness of 8µm is proposed for the subsequent growth of CMT. Rocking curves were recorded from a single thick CdTe/GaAs epilayer for wavelengths in the range 0.69-1.95A at the Daresbury SRS, and this data is extrapolated to infinite absorption to obtain an estimate of the rocking curve width representative of the surface of a thick layer. A number of models which attempt to describe the reduction in threading dislocation density with increasing thickness are reviewed and a new model based on the coalescence of like dislocations is developed. The models are compared to published data for layers with misfit in the range 0.23-14.6%. The models previously developed by Tachikawa and Yamaguchi and by Durose and Tatsuoka are shown to be the more appropriate for describing the dislocation density distribution in highly mismatched layers. Results of the transmission electron microscopy of CdTe/GaAs epilayers, both in plan view and cross-section, showing the character of dislocations threading through thick CdTe buffer layers are presented. Many dipoles composed of 30º type dislocations with Burgers vectors parallel to the interface were observed and found to adopt an orientation whereby the component dislocations had no effect on misfit strain. In cross-section, 30º type dislocations with Burgers vectors inclined to the interface were found to be numerous, 60º and screw type threading dislocations were also observed, but the cross-section projection axis made analysis of these types difficult. The screw and edge components of 30º , 60º and screw type threading dislocations are compared and it is found that the Burgers vector component causing layer tilt is of magnitude (a(_o)/2) for each type. Annealing of CdTe/GaAs epilayers under di-methyl cadmium flow was found to have no deleterious effect on layer morphology but did not result in a narrower X-ray rocking curve. Based upon HRXRD FWHM, 8µm thick CdTe buffer layers grown by MOVPE are estimated to have a dislocation density of about 3xl0(^8)cm(^-2). Even after many of the threading dislocations have been bent over at the CdTe/CMT interface, their density in MOVPE grown CMT/CdTe/GaAs is still greatly in excess of the l0(^5)cm(^-2) desired. The issues discussed and conclusions drawn in this thesis represent a thorough study of the continuing progress towards high quality MOVPE growth of CMT.
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Mui, Wing-ki, and 梅詠琪. "Studies of Ga vacancy related defects in GaSb." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2002. http://hub.hku.hk/bib/B31226541.
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Coomer, Byron James Fraser. "A first principles study of radiation defects in semiconductors." Thesis, University of Exeter, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.326953.
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Collins, Reuben T. McGill T. C. "Electronic properties of heterostructures and defects in compound semiconductors /." Diss., Pasadena, Calif. : California Institute of Technology, 1985. http://resolver.caltech.edu/CaltechETD:etd-03262008-142511.
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Edwardson, Charlene. "Positron studies of defects in thin films and semiconductors." Thesis, University of Bath, 2013. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.577748.
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Positron studies of defects in thin films and semiconductors are reviewed. The results obtained from experimental studies of Doppler broadening of annihilation radiation (DBAR) from variable energies are presented. Normalisation methods for the DBAR parameters S and W have been developed, allowing for direct comparisons of the results for different samples taken over long periods of time. The evaluation of the P:V parameter, the peak-to-valley ratio in a full annihilation spectrum, has been improved via a correction method that produced a fourfold increase in sensitivity to o-Ps annihilation. The spectrum ratio curve technique was improved and developed to investigate the chemical composition of the environment surrounding a positron-trapping defect. By fitting to multiple-element and/or defect-type responses the percentage of that particular element or defect contained within the sample could be found. Ratio curves were found to rely on the positron affinity to different vacancy types. Beam-based Doppler broadening spectroscopy, variable-energy positron annihilation spectroscopy (VEPAS), was used as a probe of oxide film and film/substrate interface characteristics. Different film growth methods were found to play a significant role in defining the features of films and their interfaces. Vacancies have a profound effect on the properties of semiconductor-type devices. A range of different structures and the effects of implantation have been investigated. VEPAS has been found to be useful in studying the more exotic types of materials, silica aerogel and niobium.
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Capaz, Rodrigo Barbosa 1968. "Ab initio studies of semiconductors : defects, surfaces and interfaces." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/10812.
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Pi, Xiaodong. "Positron annihilation spectroscopy of sub-surface defects in semiconductors." Thesis, University of Bath, 2003. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.426150.
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Sun, Baozhou. "Vibrational lifetimes of hydrogen and oxygen defects in semiconductors." W&M ScholarWorks, 2005. https://scholarworks.wm.edu/etd/1539623477.
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Characterization of defect and impurity reactions, dissociation, and migration in semiconductors requires a detailed understanding of the rates and pathways of vibrational energy flow and of the coupling mechanisms between local modes and the phonon bath of the host material. Information on the inelastic microscopic interaction can be obtained by measuring the lifetime of local vibrational modes. This dissertation presents lifetime measurements of hydrogen and oxygen defects in semiconductors by means of time-resolved infrared pump-probe spectroscopy.;First, we measured the vibrational lifetime of H- and D-related bending modes in Si and other semiconductors. Time-resolved pump-probe and linewidth measurements reveal that the lifetime of bending modes can be explained by an energy gap law, i.e., the decay time increases exponentially with increasing decay order.;Second, we present the vibrational lifetime measurements of a selection of Si-H stretch modes in crystalline Si. The lifetimes of interstitial-type defects are found to be a few picoseconds, whereas vacancy-type defects have lifetimes up to 300 picoseconds. The strong dependence of lifetime on the defect structure suggests that pseudolocalized modes are involved in the relaxation of the hydrogen stretch modes in Si. It is found that the energy relaxation of Si-H stretch modes does not decay by lowest order, i.e., low frequency modes are involved in the decay process.;Furthermore, we performed lifetime measurements of interstitial oxygen in Si and Ge. The lifetime of 17Oi in Si is half of 16Oi and 18Oi. A calculation of the three-phonon density of states shows that 17Oi lies in the highest phonon density resulting in the shortest lifetime. The lifetime of the 16Oi mode in Ge is measured to be 10 times longer than in Si. The interaction between the local modes and the lattice vibrations is discussed according to the activity of phonon combination.;These studies elucidate the dynamics of energy dissipation and vibrational decay channels of point defects in semiconductors. They provide a better understanding of the dissociation of Si-H and Si-O bonds and the strong hydrogen and deuterium isotope effect found in H-passivated semiconductor devices. The experimental results provide an indispensable benchmark for future theoretical investigations.
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Irvine, A. C. "Lattice defects in As-grown and irradiated GaAs, AlGaAs and InGaGs." Thesis, University of Sussex, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334991.
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The alloying of two or more semiconducting compounds is a powerful means of tailoring the properties of semiconductor devices, since material parameters generally display a continuous shift with composition. For the same reason, observing the characteristics of a defect across a range of alloys is a useful way of gaining infonnation on the defect's microscopic structure. In this work, Schottky diodes are employed to study lattice defects, both as-grown and created by irradiation, in the alloys AlxGal-~ (O~x~O.27) and InxGal_~ (O~x~O.18), grown by the Metal~rganic Chemical Vapour-phase Deposition (MOCVD) and Molecular Beam Epitaxy (MBE) techniques respectively. The Deep-Level Transient Spectroscopy (DLTS) method is used in conjunction with measurements, detennined fram capacitance-voltage characteristics, of the immobile space-charge concentration, Nt, as a function of distance fram the Schottky contact. InxGal_~ is lattice mismatched in growth on GaAs substrates and, as growth proceeds, the InxGal_~ in-plane lattice parameter increases towards its bulk value through the introduction and glide of dislocations at the InxGal_~~s interface. Nt profiles measured in relaxed InO.04sGaO.955As on GaAs structures show a substantial degree of carrier depletion near this interface, and similar features are observed in an Ino.lgGaO.8~-GaAs structure and in a GaAs layer deposited on a part-relaxed InO.2GaO.8As sandwich layer. A GaAs epilayer grown on GaAs as a control, on the other hand, shows no evidence of carrier trapping. It is clear that this depletion is evidence of defects related to the relaxation process. DLTS studies reveal the presence, confinned by photocapacitance quenching experiments, of the technologically important EL2 defect in the relaxed InxGa1-xAs layers, though not in the relaxed GaAs sample This represents the first time that EL2 has been observed in InxGal_~ grown by molecular-beam epitaxy (MBE). A reason for the non-observation of EL2 in the GaAs layer is put forward on the basis of strain relief considerations, and a model for EL2 fonmation in these samples is suggested. Profiling of the EL2 concentration in InO.045CaO.955As by DLTS reveals a sharply peaked distribution and indicates the absence of EL2 within ~O.4pm of the InO.045Cao.955As-GaAs interface. Consequently, it is proposed that EL2 fonmation occurs near the free surface during growth, and depends on the nucleation of dislocation half-loops. An existing strain-thickness relation is adapted on this basis to produce a model for EL2 fonmation. Several qualitative aspects of the experimental data are explained in this way. Proton irradiations were perfonned on InxGal_~s, CaAs and AlxCal_~ samples at 85K, and it was seen that, within experimental error, the introduction rates of the main DLTS-detected electron traps were independent of alloy camposition, though a marked variation in E3 emission energy with camposition was noted. More significantly, the N+ recovery stages observed below 300K in GaAs were shifted to lower temperature in AlxCal_~s. It is suggested that this may be explained simply by the small size of an aluminium atom relative to gallium. The complex implications of this observation for defect annealing in compound alloys are discussed, and a qualitative model is presented.
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Zhu, Congyong. "Deep level defects study of arsenic implanted ZnO single crystal." Click to view the E-thesis via HKUTO, 2008. http://sunzi.lib.hku.hk/hkuto/record/B40987759.
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Zhu, Congyong, and 朱從佣. "Deep level defects study of arsenic implanted ZnO single crystal." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2008. http://hub.hku.hk/bib/B40987759.
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柯俊達 and Chun-tat Or. "Optical characterization of defects in GaN." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2001. http://hub.hku.hk/bib/B31226607.
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Deane, Steven Charles. "The kinetics and equilibria of defects in hydrogenated amorphous silicon thin film transistors." Thesis, University of Cambridge, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239729.
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Neto, Frederico Ayres de Oliveira. "Propriedades estruturais, eletrônicas e ópticas dos materiais semicondutores \"HgI IND.2\" e \"ZnI IND.2\" e de defeitos em \"HgI IND.2\"." Universidade de São Paulo, 2005. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-05122006-114829/.
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O iodeto de mercúrio em sua fase vermelha, \"alfa\"-\"HgI IND.2, é um material semicondutor que desperta grande interesse tecnológico devido à sua potencial aplicação como detector, a temperatura ambiente, de raios-\"gama\" e X. Sua imediata aplicação como detector de radiação, no entanto, ainda sofre algumas restrições devido às dificuldades de controle sobre a concentração de defeitos pontuais e extensos, durante sua síntese, e sua fácil degradação quando exposto ao ambiente. A presença destes defeitos gera uma redução na mobilidade de portadores de carga, diminuindo a eficiência de detecção. Neste trabalho, realizamos uma investigação teórica das propriedades estruturais, eletrônicas e ópticas do \"alfa\"-\"HgI IND.2\" e do \"ZnI IND.\", cuja estrutura cristalina é análoga à do \"alfa\"-\"HgI IND.2\". Estudamos, também, o comportamento de tais propriedades do material contendo vacâncias de Hg e de I para entendermos o papel desempenhado por estes defeitos nas propriedades do material. Na análise dos resultados, sempre que possível, são apresentadas comparações com outros resultados teóricos e com dados experimentais. Nossos cálculos foram efetuados dentro do formalismo do funcional da densidade em combinação com duas diferentes aproximações para o termo de exchange e correlação. Utilizamos o método Augmented Plane Wave plus local orbitals (APW+lo), que é um método de primeiros princípios e inclui todos os elétrons do sistema (all electron). Adicionalmente, foram utilizados esquemas que incluem efeitos relativísticos e polarização de spin. O estudo dos defeitos foi simulado através do esquema da supercélulaMercuric iodide \"alfa\"-\"HgI IND.2 in its red tetragonal crystalline phase is a semiconducting material of great technological interest due to the potential applications as a detector for y- and X-ray spectroscopy to be operated at room temperatures.
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Stehr, Jan Eric [Verfasser]. "Point defects in oxide and nitride semiconductors / Jan Eric Stehr." Gießen : Universitätsbibliothek, 2011. http://d-nb.info/1063178371/34.
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Fujita, Naomi. "Modelling of point and extended defects in Group IV semiconductors." Thesis, University of Exeter, 2009. http://hdl.handle.net/10036/90563.
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In this thesis first-principles calculations of point and extended defects in diamond and silicon are reported. In single crystal diamond grown by chemical vapour deposition (CVD) dislocations are observed as mixed-type 45° and edge-type dislocations lying along <100> with 1/2<110> Burgers vectors. Results are presented on the core structures, core energies and electrical properties of both types of dislocations and their interaction with nitrogen is investigated. Then the focus turns to the brown diamond problem. Despite concerted research efforts, the origin of the brown colouration of diamond is still under discussion. Recently, the attention was drawn to vacancy-related defects. Experiments on type IIa diamonds indicate that the brown colour is caused by vacancy-type extended defects, however the shape and size of these defects remained unclear. In this work, the structural, electrical and optical properties of large spherical vacancy clusters and thin vacancy disks are investigated by means of density functional theory and the calculations are compared with recent experimental measurements on brown diamond. High pressure high temperature treatment (HPHT) of brown type Ia diamonds above 2000°C results in the loss of the brown colour and the formation of nitrogen-vacancy defects. The generation of such defects requires a source of mobile vacancies during the annealing process. It is suggested that the vacancy cluster model described in this thesis can explain the observed annealing behaviour since the break-up of the clusters leads to a supersaturation of mobile vacancies which readily complex with substitutional nitrogen atoms present in the material. Therefore, the effect of HPHT treatment of brown type Ia diamond is investigated by studying the formation energies of common and rare defects and estimates of their equilibrium concentrations at different annealing stages are given. Finally, an open problem also involving nitrogen, but in a different group IV semiconductor is considered. In Czochralski-silicon, nitrogen-related shallow thermal donors are formed between 500 and 750°C. Until now the exact chemical composition and atomic structure of these defects are not well established. Here, it is shown that NO and NO_2 belong to the family of nitrogen-oxygen related shallow thermal donors. Based on the law of mass action the equilibrium defect concentrations are predicted. Finally, the theoretical results are compared to recent Fourier transform infrared (FTIR) spectroscopy measurements.
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Chilton, Neil Barry. "A slow positron implantation spectroscopy study of defects in semiconductors." Thesis, University of East Anglia, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303017.
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Cavaco, Ana Margarida Rocha de Oliveira. "Radiation-induced defects in quantum-size structures of A3B5 semiconductors." Doctoral thesis, Universidade de Aveiro, 2011. http://hdl.handle.net/10773/3728.
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Doutoramento em FísicaAs estruturas quânticas de semicondutores, nomeadamente baseadas em GaAs, têm tido nos últimos vinte anos um claro desenvolvimento. Este desenvolvimento deve-se principalmente ao potencial tecnológico que estas estruturas apresentam. As aplicações espaciais, em ambientes agressivos do ponto de vista do nível de radiação a que os dispositivos estão sujeitos, motivaram todo o desenrolar de estudos na área dos defeitos induzidos pela radiação. As propriedades dos semicondutores e dos dispositivos de semicondutores são altamente influenciadas pela presença de defeitos estruturais, em particular os induzidos pela radiação. As propriedades dos defeitos, os processos de criação e transformação de defeitos devem ser fortemente alterados quando se efectua a transição entre o semicondutor volúmico e as heteroestruturas de baixa dimensão. Este trabalho teve como principal objectivo o estudo de defeitos induzidos pela radiação em estruturas quânticas baseadas em GaAs e InAs. Foram avaliadas as alterações introduzidas pelos defeitos em estruturas de poços quânticos e de pontos quânticos irradiadas com electrões e com protões. A utilização de várias técnicas de espectroscopia óptica, fotoluminescência, excitação de fotoluminescência e fotoluminescência resolvida no tempo, permitiu caracterizar as diferentes estruturas antes e após a irradiação. Foi inequivocamente constatada uma maior resistência à radiação dos pontos quânticos quando comparados com os poços quânticos e os materiais volúmicos. Esta resistência deve-se principalmente a uma maior localização da função de onda dos portadores com o aumento do confinamento dos mesmos. Outra razão provável é a expulsão dos defeitos dos pontos quânticos para a matriz. No entanto, a existência de defeitos na vizinhança dos pontos quânticos promove a fuga dos portadores dos níveis excitados, cujas funções de onda são menos localizadas, provocando um aumento da recombinação nãoradiativa e, consequentemente, uma diminuição da intensidade de luminescência dos dispositivos. O desenvolvimento de um modelo bastante simples para a estatística de portadores fora de equilíbrio permitiu reproduzir os resultados de luminescência em função da temperatura. Os resultados demonstraram que a extinção da luminescência com o aumento da temperatura é determinada por dois factores: a redistribuição dos portadores minoritários entre os pontos quânticos, o poço quântico e as barreiras de GaAs e a diminuição na taxa de recombinação radiativa relacionada com a dependência, na temperatura, do nível de Fermi dos portadores maioritários.
Quantum size semiconductor structures, namely those based on GaAs, have experienced an outstanding development in the past twenty years. This development is mainly due to the technological potential these structures present. Space-based telecommunications in harsh radiation environments motivated a run off of studies in the field of radiation-induced defects. Semiconductor properties and semiconductor device performance are highly influenced by the presence of structural defects, particularly those induced by irradiation. Properties as well as processes of creation and transformation of defects are expected to be substantially modified when moving from a bulk semiconductor to corresponding low-dimensionality structures. The main goal of this work was to study the radiation-induced defects in quantum-size heterostructures composed of GaAs and InAs. The changes introduced by radiation defects have been evaluated in structures comprising quantum dots and quantum wells subjected to irradiation with electron and protons. The use of several optical spectroscopy techniques, namely photoluminescence, photoluminescence excitation and time-resolved photoluminescence, allowed the characterization of different structures in the as-grown and irradiated state. A higher radiation hardness of the quantum dots as compared to quantum wells and corresponding bulk materials has been clearly established. This higher resistance is mainly due to the higher localization of the carrier wavefunction with increasing confinement. Another probable reason is the expulsion of mobile defects into the surrounding barrier material. However, the existence of defects in the neighbourhood of the quantum dots promotes tunnel escape of carriers from the excited dot states, whose wavefunctions are less localized, to the defects, causing an increase in the non-radiative recombination and, consequently, a decrease in device luminescence. A rather simple model for the carrier statistics out of equilibrium which reproduces quite well the luminescence results as a function of temperature allowed to demonstrate that the quantum dot photoluminescence quenching with increasing temperature is determined by two factors: the minority carrier redistribution between the quantum dots, quantum well and GaAs barriers, and the decrease in the radiative recombination rate related to the temperature dependence of the Fermi level of the majority carriers.
FCT - SFRH/BD/1264/2000
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Fell, Timothy S. "A quantitative EBIC study of dislocations and their interaction with impurities in silicon." Thesis, University of Oxford, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305415.
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Boucher, Jason. "Studies of GaAs Solar Cells Grown by Close-Spaced Vapor Transport." Thesis, University of Oregon, 2017. http://hdl.handle.net/1794/22284.
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While photovoltaic (PV) manufacturing is on track to provide a substantial portion of world electricity generation, the growth of the industry is likely to be lower than desired to meet targets designed to mitigate climate change. Many different PV technologies have been developed, but PV modules based on Si are the dominant technology due to its low cost and relatively high energy conversion efficiencies. PV modules based on III-V materials are primarily used for aerospace applications due to their high cost and record-setting efficiencies. Traditional manufacturing techniques for III-V PV require expensive precursors, and have high capital costs and low throughput. Close-spaced vapor transport (CSVT) is an alternative technique for deposition of III-V materials that was invented in the 1960s but has not been fully developed for the production of PV devices. This work describes progress towards high efficiency solid-state GaAs solar cells produced by CSVT.
Previous results have demonstrated good electronic quality of CSVT GaAs using photoelectrochemical cells, but such devices have not been demonstrated to be commercially practical. This work investigates the potential of CSVT to produce high-efficiency III-V PV by fabricating and characterizing GaAs films and simple homojunction solar cells. Chapter I describes the motivation and state of III-V PV research, and establishes basic device physics background. Chapter II gives details of film growth and device design and fabrication. Chapter III gives an overview of the film and device characterization methods employed. Chapter IV explores the primary limitations in the efficiency of the homojunction solar cells fabricated for this study and discusses some practical concerns in translating the technique to a manufacturing environment. Chapter V explores the electronically-active defects in both $n$-type films and in $p$-type absorbers of solar cells, which would be likely to limit the efficiency of devices optimized considering the results presented in Chapter IV. Chapter VI discusses some of the possible future directions for applying CSVT to more advanced device structures which are more commercially relevant, including the growth on alternative substrates and growth of ternary materials for passivating layers or multijunction cells.
This dissertation includes previously published and unpublished co-authored material.
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Leary, Paul William. "A first principles study of light impurities in semiconductors." Thesis, University of Exeter, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.390165.
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Armstrong, Andrew M. "Investigation of deep level defects in GaN:C, GaN:Mg and pseudomorphic AlGaN/GaN films." Columbus, Ohio : Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1164038818.
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Dixon, Richard H. "The characterisation of defects in III-V semiconducting compounds by electron microscopy." Thesis, University of Surrey, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.279689.
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Beglitis, N. "First-principles studies of surface defects of model metal-oxide semiconductors." Thesis, University College London (University of London), 2011. http://discovery.ucl.ac.uk/1324515/.
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In this thesis, three different model metal-oxide semiconductor systems will be discussed. First, the impact of hydroxyl vacancies, OHvac, on the geometry, electronic structure, and mechanical properties of single-walled aluminosilicate, (Al2SiO7H4)N, and aluminogermanate, (Al2GeO7H4)36, nanotubes is investigated. It is found that, with the exception of one OHvac localised on the outer wall of the (Al2GeO7H4)36 tube, these defects induce occupied and empty states in the band gap. Those states are found to be highly localised both in energy and in real space. Different magnetisation states are also found, depending on both the chemical composition and the specific side with respect to the tube cavity. The focus of the thesis then shifts to one of the most important and well-studied metaloxide surfaces, the rutile TiO2(110) surface. The reactivity of the surface is revisited, in view of the discrepancy between theory and experiment on the interaction between molecular oxygen and surface hydroxyls. This discrepancy is resolved by proposing that excess charge, associated with the oxygen vacancy and originating from Ti interstitials, is present on the surface. This surface charge opens new reaction channels not theoretically possible otherwise. The study utilises hybrid Density Functional Theory (DFT) calculations and Scanning Tunneling Microscopy (STM) simulations to provide evidence for the proposed surface charging. The last part of the thesis focuses on another surface of TiO2, the (011) surface. TiO2(011) has recently attracted attention due owing to its reported high photocatalytic activity. Several proposed structures of the surface are inconsistent with each other. Recent developments, based on Surface X-Ray Diffraction (SXRD) data and DFT simulations, now agree on a new structure. In this part a review of the various structures is provided and further evidence is given on the validity of the new proposal by providing further insight on the appearance of the surface on the STM.
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Vasheghani, Farahani Sepehr. "Optical and electronic properties of defects and dopants in oxide semiconductors." Thesis, University of Warwick, 2013. http://wrap.warwick.ac.uk/58463/.
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Interest in semiconductor materials has continually grown over the past 60 years due to their potential use in electronic and optoelectronic device structures. Oxide semiconductors are a particular class of materials that also combine conductivity with optical transparency, properties not usually found in the same material. These transparent conducting oxides (TCOs) have been among the first oxide materials to benefit from the availability of improved epitaxial growth techniques, although perovskite oxides and heterostructures have also proved to be opening a new era of high mobility structures based on oxide materials. Optical and electronic properties of binary oxides, specifically, high quality CdO and SnO2 epi- taxial films have been investigated in this thesis. The main band structure quantities, the band gap and band edge effective mass of CdO has long been a subject of controversy due to the degeneracy of this material. The lowest carrier concentration for an as-grown CdO film is 1-2×1019 cm−3. This brings about further difficulties in determining the optoelectronic properties due to conduction band filling and many body effects. The effective mass value is of particular importance in carrier mobility studies. Simulation and analysis of data collected from Hall effect, mid- and near-infrared reflectance measurements together with optical absorption spectroscopy enabled the band gap and band edge effective mass values to be determined at room temperature. Variations of the band gap, band edge effective mass, high frequency dielectric constant and the Fermi level with temperature and carrier concentration, and taking into ac- count the non-parabolicity of the conduction band, the Burstein-Moss shift and band gap renormalization, revealed the 0 K band gap and band edge effective mass values of 2.31 eV and 0.266m0 at the limit of zero carrier concentration in CdO. With the emergence of sophisticated growth techniques (MBE), high quality growth has become a key property in semiconductor research as it enables further investigation into the intrinsic characteristics of these materials. Carrier mobilities in high quality SnO2(101) films grown on r-plane sapphire by molecular beam epitaxy were studied. Transmission electron microscopy revealed a high density of dislocations at the interface due to the large lattice mismatch of -11.3%, along the < 101 > direction, between the films and the substrate, with an exponential decrease towards the surface of the films. Carrier mobility modelling proved to be impossible if a constant density of threading dislocations was assumed, however, by introducing a layer-by-layer model for the simulation of the mobility as a function of carrier concentration, the donor nature of dislocations in epitaxial SnO2 films was revealed. The deformation potential produced by the presence of these defects has been shown to be the dominant scattering mechanism for carrier concentrations above the Mott transition level of SnO2. Finally, the surface electronic structure of antimony-doped SnO2 films has been studied by the Hall effect, infrared reflectance, X-ray photoemission spectroscopy and electrochemical capacitance-voltage measurements. The bulk Fermi level was determined by carrier statistics calculations and used to obtain the degree of surface band bending. Modelling the surface energy bands through the capacitance-voltage spectra, revealed that SnO2 has downward band bending and surface electron accumulation. The respective variations were attained as a function of depth and composition of the samples.
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Al-Abdulmalik, Dana A. "Evolution of vacancy-type defects in semiconductors : a positron annihilation study." Thesis, University of Bath, 2007. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.442881.
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Jokela, Slade Joseph. "Stability and structure of hydrogen defects in zinc oxide." Online access for everyone, 2006. http://www.dissertations.wsu.edu/Dissertations/Fall2006/s_jokela_122106.pdf.
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Benjamin, Anne Laura. "Scanning Tunneling Microscopy Studies of Defects in Semiconductors: Inter-Defect and Host Interactions of Zn, Er, Mn, V, and Co Single-Atom Defects in GaAs(110)." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu15254254578788.
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Huang, Yan, and 黃燕. "Some studies of structural and point defects in gallium nitride and their influence in determining the properties of the bulk material,its Schottky contacts, P-N junctions and heterostructures." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2005. http://hub.hku.hk/bib/B31559670.
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Mari, Ruaz Hussain. "DLTS characterisation of defects in III-V compound semiconductors grown by MBE." Thesis, University of Nottingham, 2011. http://eprints.nottingham.ac.uk/14211/.
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The interest in the growth of III-V compound semiconductors such as GaAs and AlGaAs on high index planes has increased tremendously over the last few years. The structural, optical and electrical properties III-V based structures are found to improve by, growing on (nil) planes. For example the amphoteric nature of silicon (Si) facilitates the Molecular Beam Epitaxy (MBE) growth of p-type GaAs/AlGaAs heterostructures on (311)A that have higher hole mobilities than those based on the conventional Be-doped p-type on (100) GaAs plane. The incorporation of intentional impurities, such as Si or Be in III-V semiconductors, have desirable effects in terms of controlling the electrical conductivity of the materials. However, other unintentionally incorporated impurities and defects have deleterious effects on the electrical and optical properties of III-V based devices. In this thesis, current-voltage-temperature (I-V-T), capacitance-voltage (C-V) Deep Level Transient Spectroscopy (DLTS) and Laplace DLTS techniques have been used to investigate defects in several MBE III-V epilayers and modulated structures grown both on the conventional (100) and non-(100) GaAs substrates. These include: (i) n-type silicon-doped (n11)B (n = 2-5) GaAs epitaxial layers; (ii) n-type silicon-doped (100) and (311)B GaAs/AlGaAs multi-quantum well (MQW); (iii) n-type silicon-doped (100) MQWs grown at different substrate temperatures, arsenic overpressures and arsenic species (As2 and As4); (iv) p-type Be-doped (100) and (311)A AlGaAs epitaxial layers; (v) GaAs/AlGaAs two dimensional electron gas (2DEG); (vi) commercially grown high electron mobility transistors (HEMT). The main findings of the experimental results are given in the following: 1. n-type silicon-doped (n11)B (n = 2-5) GaAs: the overall density of defects is highest in (211)B and lowest in (511)B. The number of detected defects is minimum in (511)B. The common carbon background impurity in MBE is observed only in (100) substrates. 2. n-type silicon-doped (100) and (311)B GaAs/AlGaAs MQWs: the concentration of the only trap is higher in (100) than in (311)B orientation. Furthermore, in (100) the observed trap electrically charged, while it has neutral nature in (311)B. 3. n-type silicon-doped (100) MQWs grown at different substrate temperatures, arsenic overpressures and arsenic species (As2 and As4): the average trap concentration for As2 samples is lower than Asa samples. In addition, the concentration of the common VAs-related point defect decreases with increasing growth temperature and arsenic overpressure. 4. p-type Be-doped (100) and (311)A AlGaAs: the number of hole traps in (311)A decreases from five to one when the Be-doping level varies from 1 x 1016 cm-3 to 1 x 1017 cm3. For (100) the detected hole levels are three, four and two for Be-concentrations of 1ix 016 cm -3 , 3x1016 cm-3 and 1x1017 cm 3, respectively. In addition, an electron emitting level is observed only in (100) samples doped to 1 x1017 cm 3. 5. GaAs/AlGaAs 2DEG and HEMT devices: one major defect, assigned to the DX center, is common in both in-house grown 2DEG and commercially HEMT devices. It behaves as a generation-recombination center, and its concentration is directly related to the silicon doping level in the AlGaAs layer. The HEMT devices which showed poor frequency response are found to have the highest concentration of the DX center.
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Vaseashta, Ashok K. "Photonic studies of defects and amorphization in ion beam damaged GaAs surfaces." Diss., This resource online, 1990. http://scholar.lib.vt.edu/theses/available/etd-08082007-170507/.
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