Growth of semiconductors by the close-spaced vapor transport technique: A review
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Growth of semiconductors by the close-spaced vapor transport technique: A review G. PerrierandR. Philippe GREPMesures Physiques, 28, Av. Leon Jouhaux, 42023 St-Etienne Cedex 02, France
J.P. Dodelet INRS-Energie, C. P. 1020, Varennes, Quebec, J0L2P0 Canada (Received 16 November 1987; accepted 3 June 1988) The close-spaced vapor transport (CSVT) is an efficient and cost-effective technique that allows the growth of polycrystalline as well as epitaxial thin layers of semiconductors. The close spacing between a source and a substrate, introduced in 1963 as a special feature in the vapor phase method, has been applied to about 18 semiconductors with a special focus on CdTe and GaAs. This paper reviews the close-spaced technique, the models presented to explain the film growth rates, the transport reactions, and film characteristics for all the semiconductors that have been obtained by CSVT. All-thin-film structures for solar cells or other applications are certainly feasible with the use of the CSVT technique when a good lattice matching exists between the successive layers.
I. INTRODUCTION Semiconductor thin films are widely used in the production of important technological applications like optoelectronic or photovoltaic devices. Numerous processes are available for growing semiconductor layers like vacuum deposition, hot wall vacuum evaporation, electron or molecular beam evaporation, chemical vapor deposition, transport from liquid or vapor phase, sputtering, gas-solid reactions, spray pyrolysis, screen printing, electrodeposition, etc. Among these processes, vapor phase transport has been used for several years in order to deposit epitaxial layers of semiconductor materials. This process is based on heating to different temperatures the source of a material to be deposited and a substrate for the epitaxy. Usually, a transporting agent diluted in a carrier gas reacts with the source to form a volatile compound that then migrates to the substrate where the reverse reaction takes place. An interesting feature was added in 1963 to the vapor phase transport technique, almost simultaneously by Sirtl and by an RCA team, with the close spacing of the source and substrate. 1 ' 5 This specification brought new characteristics to the method, which was initially named "sandwich method," then most commonly "close-spaced vapor transport" (CSVT). Particularly, the transport conditions became largely independent of the conditions elsewhere in the system, providing that the spacing between the source and the substrate is less than about 1/10 of the source and substrate dimensions.2 In sealed tubes, the transporting agent is not consumed in the material transport (providing no side reactions) and is therefore available for continuous re-use between the source and the subJ. Mater. Res. 3 (5), Sep/Oct 1988
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strate. Iii open tube conditions, the transporting agent is usually introduced at a constant pressure with the carrier gas passing through the reactor at low flow rate. In these conditions, the CSVT
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