Browsing by Author "Tavendale, AJ"

Now showing 1 - 13 of 13
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    An attempt to detect electrochemical doping of silicon with arsenic by Rutherford backscattering analysis
    (Australian Atomic Energy Commission, 1983-02) Tavendale, AJ; Lawson, EM
    Rutherford scattering analysis with 2.0 MeV 4He+ ions failed to detect doping of silicon substrates with arsenic following cathodic electroplating. This is in contrast with the claims of J. Antula [J. Appl. Phys., 48:2581, 1977] that electromigration leads to the formation of n-type, arsenic-doped, near-surface layers in silicon. Arsenic was detected only in the surface oxide layer formed during plating. Complementary thermoprobe measurements also showed no doping effects in the silicon substrates.
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    The behaviour of high purity semiconductor surface-barrier nuclear radiation detectors at low temperatures
    (Australian Atomic Energy Commission, 1973-04) Lawson, EM; Tavendale, AJ
    The characteristics of a germanium and a silicon surface barrier detector have been examined at low temperatures (78 to 5 K). Preliminary results have also been obtained from a gallium arsenide detector. All detectors were fabricated from high purity material. Below some critical temperature (10 K in germanium and 32 K in silicon) the spectral response to y-rays deteriorated markedly, particularly for low bias. Near liquid helium temperature best resolutions of 10.0 keV at 662 keV and 3.0 keV at 122 keV were obtained with the germanium and silicon detectors respectively. Relative efficiency measurements found no change in the sensitive depth with temperature in contrast to the indications of the capacitance. A model based on field-assisted detrapping is proposed to account for the fact that sensitive depth is independent of temperature. The behaviour of the capacitance and the existence of slow components in the pulse risetime are explained in terms of the equivalent circuit of the detector. The energy resolution of the gallium arsenide detector did not change on cooling to 7 K where a resolution of 3.9 keV at 60 keV was measured.
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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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    Deep level transient spectroscopy of y-ray induced defects in germanium
    (Australian Atomic Energy Commission, 1980-12) Pearton, SJ; Williams, AA; Tavendale, AJ
    Deep level transient capacitance spectroscopy has been used to examine γ-ray induced defect centres in germanium crystals grown under widely varying conditions. A deep acceptor level at Eν + 0.38 eν has been observed for the first time in all p-type samples; this was removed by annealing at 675 deg C for three hours. A new deep donor level at Eс - 0.42 eν observed in n-type material was not removed by this procedure.
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    Hydrogenation of deep-level hole-trapping centres associated with grain boundaries in germanium.
    (Australian Atomic Energy Commission, 1983-04) Tavendale, AJ; Pearton, SJ
    Effects of the hydrogenation of deep level, hole-trapping centres associated with grain boundaries incorporated in diodes from n- and p- type germanium have been examined by deep level transient capacitance spectroscopy and measurement of reverse bias leakage current. Significant reductions in diode leakage current (by factors of 2 to 10 at 77 K) and suppression of deep level centres were observed following exposure to a low pressure (0.5 torr), radio-frequency-induced hydrogen plasma at 300oC for 2 hours; no reversal was observed after a subsequent vacuum anneal at the same temperature and time.
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    A large volume, multi-element Ge(Li) spectrometer
    (Australian Atomic Energy Commission, 1970-11) Lawson, EM; Tavendale, AJ; Dawson, AC
    To make use of the good energy resolution of Ge(Li) spectrometers of r-ray energies of several MeV, the sensitive volume must be increased to beyond 100 cm3. This volume is generally only attainable by operating several smaller spectrometers in parallel. Three coaxial Ge(Li) detectors were fabricated, assembled in a cryostat and operated in parallel. The spectral performance was relative efficiency of this multi-element spectrometer were investigated for r-rays of energies between 1 and 10 MeV. High energy r-rays (5-10 MeV) were obtained by thermalising neutrons from a Pu-Be source and then absorbing them in materials with high cross sections for radiative capture. The experience gained is summarised and alterations to future multi-element spectrometers are proposed.
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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 nature of the Ev + 0.23 eV and Ev + 0.38 eV gamma-induced centres in Ge.
    (Australian Atomic Energy Commission, 1982) Pearton, SJ; Tavendale, AJ
    All p-type Ge grown by the Czochralski technique from silica crucibles under an H sub 2 atmosphere shows two dominant acceptor defects on gamma irradiation. Measurements by DLTS are reported which support the hypothesis that these centres (E(v) + 0.23 eV E(v) + 0.38 eV) are most likely due to complexes between oxygen and lattice vacancies.
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    The operation near liquid helium temperature of a gold-barrier hyper-pure germanium detector for gamma-rays
    (Australian Atomic Energy Commission, 1971-02) Lawson, EM; Tavendale, AJ
    Diode characteristics and spectral response to 137Cs γ-rays of a gold-barrier detector made from hyper-pure germanium (net donor concentration 3 x 10 11cm-3) were examined over the temperature range 5 -78°K. Trapping at the primary shallow donor is believed responsible for poor energy resolution at low temperatures. At 5°K a best resolution of 10 keV FWHM was obtained. Efficiency measurements indicate no change in depletion depth on cooling to 5°K with constant bias, in contrast to capacitance measurements. The latter variation, however, can be explained in terms of the response of the detector equivalent circuit to bridge frequency and carrier freeze-out effects. Field-assisted de-trapping at the primary shallow donors is believed responsible for the temperature independent depletion depth and an improvement in resolution with bias in the low temperature carrier freeze-out region (< 10°K).
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    Restoration of lithium driftability in some vacuum-grown germanium crystals for gamma-ray detectors
    (Australian Atomic Energy Commission, 1970-11) Tavendale, AJ
    Germanium crystals used for γ-ray detectors frequently exhibit slow or non-uniform lithium-ion drift. The presence of oxygen is one known cause. However, it has been found in these laboratories that in large (~ 1kg) germanium crystals grown by the Czochralski method under vacuum, the presence of a fast diffusing impurity (probably copper) also leads to variable drift. Normal, uniform drift in these crystals has been restored by using gallium-indium alloys as a getter at ~ 800°C. The method is described in detail and the effects on crystal resistivity, dislocation density and lithium drift rate are presented. Gamma-ray detectors fabricated from gettered material show high resolution characteristics.
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    Transient capacitance measurements of deep level defects introduced in y-ray compensated germanium by long-term annealing at room temperature
    (Australian Atomic Energy Commission, 1980-09) Pearton, SJ; Williams, AA; Tavendale, AJ; Lawson, EM
    Deep level transient spectroscopy (DLTS) has been applied to defect centres in γ-ray compensated germanium that has been subjected to long-term annealing at room temperature. Deep donor levels (Ec - 0.36 eV Ec - 0.20 eV) have been observed for the first time; annealing at 675ºC for 3 hours increased their concentration in proportion to the free carrier density indicating stable defect-impurity complexes. Recently irradiated samples from the original material have not shown these levels. The results support Russian work on the compensation mechanism - the formation of electically inactive vacancy-donor complexes.
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    Transient conductance spectroscopy measurements of defect states in y-irradiated n-channel silicon field effect transistors with possible y-dosemeter applications
    (Australian Atomic Energy Commission, 1980-12) Pearton, SJ; Tavendale, AJ; Williams, AA
    A deep level transient capacitance spectroscopy (DLTS) system modified for the measurement of transient conductance has been used to observe gamma-ray induced defect centres in the gate junction of 2N4416 Si field effect transistors. The defect concentrations increased linearly wth gamma-dose in the range 50 kGy to 10 x 10 3 kGy (5-1000 Mrad) for the common E(c) - 0.17 eV level and in the range 500 kGy to 10 x 10 3 kGy (50- 1000 Mrad) for the levels E(c) - 0.22 eV and E(c) - 0.44 eV. Another common level a hole trap at E(v) + 0.42 eV was the only minority trap observed. The technique may be useful for measuring gamma-fluxes in situations inaccessible to standard dosemeters (e.g. flux-mapping).