Browsing by Author "Butcher, KSA"
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- ItemDielectric properties and photoluminescence of diatomaceous silicas(Australian Institute of Physics, 2005-01-31) Jong Wah, JW; Ferris, JM; Wintrebert-Fouquet, M; Butcher, KSASilica shells produced by diatoms have been studied to investigate their potential for applications in electronic and photonic devices due to their dielectric and photoluminescent properties. Dielectric measurements for low (1k-1MHz) and high (∼1GHz) frequencies were performed on processed diatomaceous earth samples and compared with measurements for artificial porous silica samples. Photoluminescence spectra for a sample of freshwater benthic diatoms were obtained and compared with silica spectra. The ratio of the 3.2eV photoluminescence peak compared to a peak at ∼2.20eV is smaller than for pure fused silica, and there is evidence of extra shoulder peak near 2.2eV for diatogenic silica. © 2005 Australian Institute of Physics.
- ItemDigital coincidence counting - initial results(Elsevier, 2000-08-01) Butcher, KSA; Watt, GC; Alexiev, D; van der Gaast, H; Davies, JB; Mo, L; Wyllie, HA; Keightley, JD; Smith, D; Woods, MJDigital Coincidence Counting (DCC) is a new technique in radiation metrology, based on the older method of analogue coincidence counting. It has been developed by the Australian Nuclear Science and Technology Organisation (ANSTO), in collaboration with the National Physical Laboratory (NPL) of the United Kingdom, as a faster more reliable means of determining the activity of ionising radiation samples. The technique employs a dual channel analogue-to-digital converter acquisition system for collecting pulse information from a 4π beta detector and an NaI(Tl) gamma detector. The digitised pulse information is stored on a high-speed hard disk and timing information for both channels is also stored. The data may subsequently be recalled and analysed using software-based algorithms. In this letter we describe some recent results obtained with the new acquistion hardware being tested at ANSTO. The system is fully operational and is now in routine use. Results for 60Co and 22Na radiation activity calibrations are presented, initial results with 153Sm are also briefly mentioned. © 2000, Elsevier Ltd.
- ItemEffect of crucible materials on impurities in LPE-GaAs(Elsevier, 1996-03-01) Mo, L; Butcher, KSA; Alexiev, DLPE-GaAs grown in carbon, boron nitride and alumina crucibles has been examined using standard characterisation techniques including capacitance-voltage (C-V) measurements and deep level transient spectroscopy (DLTS). The epitaxial layers have net carrier concentration ranging from 5 × 1014 to 8 × 1015 carriers per cm3. DLTS data has shown that all epitaxial layers have deep level traps. © 1996, Elsevier Ltd.
- ItemEtch 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, DEtch 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.
- ItemGrowth of high purity liquid phase epitaxial GaAs in a silica growth system(Elsevier, 1995-12-01) Butcher, KSA; Mo, L; Alexiev, D; Tansley, TLLiquid phase epitaxial gallium arsenide layers, greater than 200 μm thickness and with a low net carrier concentration (NA,D ≈ 1013 cm−3) have been grown in a silicia growth system with silica crucibles. Analysis of electrical and chemical defects was carried out using capacitance-voltage (C---V) measurements, deep level transient spectroscopy (DLTS) and secondary ion mass spectroscopy (SIMS). Details of the growth procedure are given and it is shown that silicon incorporation in the growth layer is not suppressed by the addition of ppm levels of oxygen to the main hydrogen flow. © 1995, Elsevier Ltd.
- ItemHigh purity liquid phase epitaxial gallium arsenide nuclear radiation detector.(Australian Nuclear Science and Technology Organisation, 1991-11) Alexiev, D; Butcher, KSASurface 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.
- ItemA luminescence study of porous diatoms(European Materials Research Society, 2004-05) Butcher, KSA; Ferris, JM; Phillips, MR; Wintrebert-Fouquet, M; Jong Wah, JW; Jovanovic, N; Vyverman, W; Chepurnov, VA
- ItemLuminescence study of porous diatoms(Elsevier, 2005-12) Butcher, KSA; Ferris, JM; Phillips, MR; Wintrebert-Fouquet, M; Jong Wah, JW; Jovanovic, N; Vyverman, W; Chepurnov, VAThe cathodoluminescent and photoluminescent properties of the nanoporous silica frustules of various diatom strains and of natural diatom samples are presented. The spectra are observed to be similar to that of pure silica glass and the phenology is therefore believed to also be somewhat similar. A strong U-V-blue luminescence peak is commonly observed as well as a yellow peak at 2.15 eV For the more heavily silicified field-collected freshwater benthic samples, a strong red peak at 1.95 eV is also observed. The 2.15 eV peak is also more strongly evident for the field-collected samples. The U-V-blue peak is related to common silica defect structure but cathodoluminescent microanalysis shows that this emission is highly localized in the diatom samples. © 2005, Elsevier Ltd.
- ItemThe 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, SMeasurements 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.
- ItemThe 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, SMeasurements 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
- ItemPhotoluminescence and cathodoluminescence studies of diatoms - nature’s own nano-porous silica structures(Australian and New Zealand Institute of Physics, 2003-02) Butcher, KSA; Ferris, JM; Phillips, MRPhotoluminescence (PL) and cathodoluminescence (CL) data are presented for the silica frustules of some fresh water diatoms. The diatom frustules consist of a nano-porous silica structure that may possibly be exploited for optoelectronic or photonic applications. This work represents what we believe to be the first report of the CL and PL properties of this naturally occurring source of nano-porous silica.
- ItemProcess optimization and characterization of Ni-Ge-Au ohmic contacts to n+ GaAs heterostructures(Australian and New Zealand Institutes of Physics, 1994-02-09) Lumpkin, NE; Lumpkin, GR; Butcher, KSAA process for the formation of low resistance Ni-Ge-Au ohmic contacts to n+ GaAs heterostructures was optimized using multivariable screening and response surface experiments [1,2]. Of seven variables screened by a fractional factorial experiment, the strongest effects were: total Ge+Au evaporative thickness, Ge:Au ratio and post-alloy cooling time. A response surface experiment run on these three variables enabled the development of an empirical model of ohmic contact resistance (Rc), with a predicted optimum value of 0.07 ± 0.03 Ωmm. Twenty confirmation runs yielded an average Rc of 0.07± 0.04 mΩm, a reduction of 50% on the standard average process value of 0.14 ±0.1Ω mm. A non-optimized (Rc = 0.17 Ωmm) and an optimized (Rc = 0.04 Ωmm) sample were characterized using SEM-EDS, cross-sectional AEM, and XPS techniques. The non-optimized sample has prominent surface dendrites and a heterogeneous microstructure consisting of blocks of Ni0.5Ge0.4As0.1 in a matrix of Au0.7Ga0.2As0.1 and Ge-rich phases. Some of the Ge-rich crystals extend downward 50 nm into the substrate and are epitaxial to the n+ GaAs. The optimized sample has faint surface dendrites and a homogeneous fine-grained microstructure consisting of islands of Ni0.5Ge0.25As0.25 in a matrix of Au0.8Ga0.15As0.05. XPS depth profiles are in qualitative agreement with these results - the non-optimized sample shows a higher Ge content in the metal layer and less Ge in the GaAs substrate relative to the optimized sample. This work shows that 1) multivariable experimental methods can be used to optimize Ni- Ge-Au ohmic contacts to n+ GaAs, 2) the critical parameters for this process are Ge+Au layer thickness. Ge:Au ratio, and post alloy cooling time, and 3) lower Rc values are realized by effective diffusion of Ge from the metal layer into the GaAs substrate [3].
- ItemSurface passivation of high-purity germanium gamma-ray detector(Australian Nuclear Science and Technology Organisation, 1993-01) Alexiev, D; Butcher, KSA; Edmondson, M; Lawson, EMThe 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.
- ItemSurface passivation of liquid phase epitaxial GaAS(Australian Nuclear Science and Technology Organisation, 1995-10) Alexiev, D; Butcher, KSA; Mo, L; Edmondson, MPassivation 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.
- ItemVariations in the apparent optical band-gap of RPE-CVD grown indium nitride thin films(Australian Institute of Physics, 2004-02-05) Butcher, KSA; Wintrebert-Fouquet, M; Chen, PPT; Tansley, TL; Prince, KEIndium nitride is a semiconducting material with a band-gap which is in current dispute. Although a ~ 0.75 eV band-gap was announced by some international groups in 2002 [1,2], it has since been shown that all the evidence for a ~ 0.75 eV band-gap is due to deep level defects [3, 4]. Despite this there still appears to be anomolous variations in the apparent bandgap for this material. The Macquarie University Low Temperature Nitride Film Growth Facility has recently grown some very high quality indium nitride thin films by remote plasma enhanced chemical vapour deposition (RPE-CVD). This material shows a variation in the apparent band-gap, as measured by optical absorption techniques, of 1.2 eV to 1.8 eV, dependent on the growth temperature and time. SIMS results measured by the ANSTO SIMS group show that the oxygen content of the films is low and that the variation in the apparent band-gap is not correlated to oxygen content. Other film properties will be described.