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Browsing Scientific and Technical Reports by Author "Alexiev, D"

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    Deep level transient conductance spectrometer for high resistivity semiconductors using a marginal oscillator detector.
    (Australian Atomic Energy Commission, 1984-09) Alexiev, D; Tavendale, AJ
    A deep level transient conductance spectrometer for high resistivity semiconductors, using a radiofrequency (~40 MHz) marginal oscillator as a conductance detector, is described. Spectra are generated by periodically filling deep level trapping centres with carriers stimulated by a pulsed GaAs laser, and processing the trap-emptying conductance signal through an exponential Miller correlator as the sample temperature is slowly ramped. Simple capacitive coupling of samples to the oscillator tank circuit eliminates problems such as unwanted defect annealing and other material changes often associated with the high temperature techniques necessary for ohmic contact formation. Representative deep level spectra are given for semi-insulating Bridgman-grown CdTe.
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    Deep level transient spectroscopy of n-GaAs surface barrier diodes for nuclear radiation detection
    (Australian Atomic Energy Commission, 1981-01) Pearton, SJ; Alexiev, D; Tavendale, AJ; Williams, AA
    Deep level transient spectroscopy has been applied for the first time to the study of deep level defects in n-GaAs nuclear radiation detectors. Devices made from commercial bulk and epitaxial material with net donor impurity densities in the range 5 x 10 13 -3 x 10 16 cm -3 have been studied and several common levels observed. The Poole-Frenkel effect has been identified in three levels (Ev + 0.19 eV, Ec - 0.62 eV Ec - 0.73 eV) in the epitaxial GaAs. A value for the Poole-Frenkel constant of β = 4.7 ≥ 1.4 x 10-4 eV V-½ cm½ was obtained compared to the theoretical value for GaAs of 2.3 x 10-4 eV V-½ cm½.
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    Etch rates for (100) gallium arsenide using aqueous h2so4h2o and aqua regia based etchants.
    (Australian Nuclear Science and Technology Organisation, 1991-09) Keane, M; Butcher, KSA; Alexiev, D
    Etch rate experiments were carried out for (100) GaAs using etching solutions of H2SO4 :H2O2 :H2O (3:1:1 3:1:15) HCl:HNO3 (3:1) HCl:HNO3 :H2O (1: 1:1) and HCl:HNO3 :glycerol (with various dilutions of glycerol). Several differences were seen for the (100) plane compared to previous results for other crystal orientations. The sulphuric acid solutions showed much lower activation energies for etching the (100) plane. The HCl:HNO3 :glycerol solutions showed considerably lower etch rates for the (100) plane probably indicating that they etch GaAs anisotropically. For a 1:1:2 solution of HCl:HNO3 :glycerol a decrease in the etch rate of (100) GaAs was observed in the presence of stirring. This is the opposite result to what is commonly assumed for this polishing etchant. It indicates that the main polishing process attributed to this etchant is not present and in fact the polishing quality of the etchant is probably limited by the etching process which is present.
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    High purity liquid phase epitaxial gallium arsenide nuclear radiation detector.
    (Australian Nuclear Science and Technology Organisation, 1991-11) Alexiev, D; Butcher, KSA
    Surface barrier radiation detector made from high purity liquid phase epitaxial gallium arsenide wafers have been operated as χ- and γ-ray detectors at various operating temperatures. Low energy isotopes are resolved including 241Am at 40°C. and the higher gamma energies of 235U at - 80°C.
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    Liquid phase epitaxy of gallium arsenide - a review
    (Australian Nuclear Science and Technology Organisation, 1992-07) Alexiev, D
    Liquid phase epitaxy of gallium arsenide has been investigated intensively from the late 1960's to the present and has now a special place in the manufacture of wide band compound semiconductor radiation detectors. Although this particular process appears to have gained prominence in the last three decades the authors point out that its origins reach back to 1836 when Frankenheim made his first observations. A brief review is presented from a semiconductor applications point of view on how this subject developed.
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    Lithium compensation of GaAs.
    (Australian Nuclear Science and Technology Organisation, 1988-08) Alexiev, D; Tavendale, AJ
    Defects generated following Li diffusion into GaAs were studied by optical deep level transient spectroscopy (ODLTS) and deep level transient spectroscopy (DLTS). In an exploratory series of experiments the effect of Li diffusion on existing trap spectra defect generation and as a means for the compensation of GaAs was studied. The variables included diffusion temperature initial trap spectra of GaAs and annealing periods. Detailed measurements of trap energies were made.
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    The measurement of minority carrier diffusion lengths for high purity GaAs using an electron beam induced current technique
    (Australian Nuclear Science and Technology Organisation, 1990-07) Butcher, KSA; Alexiev, D; Tansley, TL; Leung, S
    Measurements of minority carrier diffusion lengths for p-type and n-type GaAs were carried out using an electron beam induced current technique. The GaAs material was grown by liquid phase epitaxy at the Australian Nuclear Science and Technology Organisation. The diffusion lengths measured for the n-type materials show good agreement with past results for material of similar purity. For higher purity p-type and n-type samples diffusion lengths were observed which are larger than any previously reported. For different electron beam voltages the observed values of diffusion length were unaffected by surface recombination. This again indicates very pure material. The diffusion length measurements reported here indicate that the LPE GaAs samples being produced by the Australian Nuclear Science and Technology Organisation's Radiation Detectors Project are of the highest quality for producing X-rays and low energy gamma ray radiation detectors.
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    The measurement of minority carrier diffusion lengths for high purity GaAs, using an electron beam induced current technique
    (Australian Nuclear Science and Technology Organisation, 1990-07-01) Butcher, KSA; Alexiev, D; Tansley, Tl; Seung, S
    Measurements of minority carrier diffusion lengths for p-type and n-type GaAs were carried out using an electron beam induced current technique. The GaAs material was grown by liquid phase epitaxy at the Australian Nuclear Science and Technology Organisation. The diffusion lengths measured for the n-type materials show good agreement with past results for material of similar purity. For higher purity p-type and n-type samples, diffusion lengths were observed which are larger than any previously reported. For different electron beam voltages the observed values of diffusion length were unaffected by surface recombination. This again indicates very pure material. The diffusion length measurements reported here indicate that the LPE GaAs samples being produced by the Australian Nuclear Science and Technology Organisation's Radiation Detectors Project are of the highest quality for producing X-rays and low energy gamma ray radiation detectors. 20 refs., 2 tabs., 4 figs
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    Neutron transmutation doping of gallium arsenide.
    (Australian Nuclear Science and Technology Organisation, 1987-12) Alexiev, D
    Neutron transmutation doping (NTD) was studied as a means of compensating p-type Cd-doped GaAs. By introducing specific donor concentrations the net acceptor level was measured and showed a progressive reduction. The NTD constant K = 0.32 donor atoms.cm3 per n.cm2 was also measured. Radiation damage caused by neutron bombardment was annealed and no additional traps were generated.
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    Neutron transmutation doping of silicon for the production of radiation detectors
    (Australian Nuclear Science and Technology Organisation, 1987-11) Alexiev, D
    P-type silicon was doped by neutron transmutation (NTD-Si) to produce high resistivity n-type silicon suitable for the production of surface barrier radiation detectors. Deep level transient spectroscopy (DLTS) analysis showed no remnant traps following annealing (850 deg C) of the NTD-Si in the presence of a phosphosilicate glass getter. Surface barrier radiation detectors constructed from this material showed no significant charge trapping and compare favourably with those constructed of float-zone (FZ) Si.
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    Surface passivation of high-purity germanium gamma-ray detector
    (Australian Nuclear Science and Technology Organisation, 1993-01) Alexiev, D; Butcher, KSA; Edmondson, M; Lawson, EM
    The experimental work consists of two parts. The first involves fabrication of hyper-pure germanium gamma ray detectors using standard surface treatment chemical etchings and containment in a suitable cryostat. Then after cooling the detectors to 77 K gamma-ray emissions from radioisotopes are resolved resolution depletion depth VR versus IR characteristics and /NA -ND / of the germanium are measured. The second part of the work involves investigation of surface states in an effort to achieve long-term stability of operating characteristics. Several methods are used: plasma hydrogenation a-Si and a-Ge pinch-off effect and simple oxidation. A-Ge and a-Si thicknesses were measured using Rutherford backscattering techniques; surface states were measured with deep level transient spectroscopy and diode reverse current versus reverse voltage plots. Some scanning electron microscope measurements were used in determining major film contaminants during backscattering of a-Si and a-Ge films. Surface passivation studies revealed unexpected hole trapping defects generated when a-Ge:H film is applied. The a-Si:H films were found to be mechanically strong, no defect traps were found and preliminary results suggest that such films will be good passivants.
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    Surface passivation of liquid phase epitaxial GaAS
    (Australian Nuclear Science and Technology Organisation, 1995-10) Alexiev, D; Butcher, KSA; Mo, L; Edmondson, M
    Passivation of the liquid phase epitaxial GaAs surface was attempted using aqueous P2S5 -NH4OH (NH4)2Sx and plasma nitrogenation and hydrogenation. Results indicate that plasma nitrogenation with pretreatment of plasma hydrogenation produced consistent reduction in reverse leakage current at room temperature for all p and n type Schottky diodes. Some diodes showed an order of magnitude improvement in current density. (NH4)2Sx passivation also results in improved I-V characteristics though the long term stability of this passivation is questionable.