University College London Hosts 4th BACG Photochemical Processing Workshop
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University Collège London Hosts 4th BACG Photochemical Processing Workshop University Collège London hosted the Fourth Photochemical Processing Workshop of the British Association for Crystal Growth (BACG) April 21,1989. The workshop followed the same successful format of the previous meetings with brief up-tothe-minute contributions. This year, 17 talks were presented, more than in previous years. Although the earlier meetings were envisaged as an annual gathering of the United Kingdom's photochemical processing community, the last two hâve attracted an increased, and welcome, involvement from other European countries, including collaboration with the European-MRS. The host and program chairman was Ian W. Boyd, who founded the laser processing group in the Department of Electrical Engineering at University Collège London. The laser processing group participâtes in the London University Interdisciplinary Research Centre (IRC) in semiconductors and optical materials. Coorganizer and treasuier was Richard Jackman, while Stuart Irvine and David Haigh contributed greatly in the overall organization within the scientific committee. The largest session covered déposition of semiconductors, from amorphous silicon to GaAs and ZnSe. S.C. Deane and W.I. Milne (Cambridge University) described photochemical vapor déposition of thin film transistors. The internai lamp technique was used where a hydrogen discharge in the upper part of the cell illuminâtes the SiH, reactant gas in the lower section. Using 1 mbar total pressure and a substrate température of 250 °C, a growth rate of 0.7 À/s was achieved. The amorphous Si:H thin films were flat to within 5-10 Â. The thin film transistor performance was comparable for the internai lamp and plasma déposition, with poorer performance if an external lamp was used. S. Rolt and K.G. Snowden (SIC Technology Ltd.) reported on the problems associated with low-temperature GaAs epitaxy by laser-induced déposition. Difficulties with maintaining a clean UV window free from reaction products were overcome with careful reactor cell design and the incorporation of a purge gas. GaAs films were grown onto AlGaAs buffered GaAs substrate at températures in the 350450°C range. Trimethyl gallium and arsine were decomposed using a 248 nm excimer laser at 100 mj/cm2/pulse. The films were epitaxial but displayed some twinning. Some encouraging assessment came from
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secondary ion mass spectroscopy, which indicated that the carbon concentration was below 5 x 1017 cm 0 . J. Hopkins et al. (Heriot-Watt University) described an alternative approach to GaAs laser déposition. An argon ion laser beam was focused onto a substrate and scanned across the surface. Décomposition of trimethyl gallium and arsine occurred on the substrate due to laser heating. A continuous 10 ^m wide stripe was deposited using 4 w power and V:HI ratio of 15:1. J.E. Hails et al. (RSRE) described the significant properties of precursors for successful laser-induced epitaxy of CdTe. For selected-area epitaxy the precursors must be therma
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