Laser-induced chemical vapor deposition of germanium and doped-germanium

Abstract

Germanium and doped-germanium polycrystalline films are formed using photolytic CO.sub.2 laser-induced chemical vapor deposition method. Germanium being transparent to IR light makes the production of high purity polycrystalline germanium and doped-germanium films from starting compounds of germane, ethylgermane diethylgermane, and triethylgermane ideally adapted to the laser induced infrared radiation provided by the tunable, continuous-wave CO.sub.2 laser which delivers infrared laser radiation in the range of 10.4 or 9.4 micrometers. Triethylgermane produces germanium in a quantity usable as a dopant. Scanning electron microscopy is used for analysis of the films. The products identified on irradiation of germane are germanium and hydrogen. Conversion rates on the order of 86% are readily obtained. On irradiation of diethylgermane and ethylgermane, ethylene, germane, germanium and hydrogen are produced. Germanium films doped with cadmium and aluminum are successfully produced by the irradiation of germane mixtures containing dimethylcadmium or trimethylaluminum, respectively. A starting material such as tetramethylgermane (TMG) which has a high vapor pressure, e.g. >70 torr and which does not have a frequency of vibration resonant with the output of the CO.sub.2 laser, is usable in the presence of a sensitizer, i.e., a substance is employed with tetramethylgermane which absorbs the energy and then subsequently reacts with a transfer energy to the TMG.