Coupled gas and surface reactions in the organometallic vapor-phase epitaxy of cadmium telluride

Abstract

We have examined the effect of the carrier gas on the kinetics of cadmium telluride deposition from dimethylcadmium (DMCd) and dimethyltellurium (DMTe) in a hot-wall glass reactor. Upon switching the gas from hydrogen to helium, the methane/ethane product ratio decreases from 4.1/1.0 to 0.0/1.0, the growth rate falls by a factor of 3.3±0.3, and the film becomes substantially rougher. These results are explained by the following reaction mechanism: DMCd and DMTe adsorb on the CdTe surface, then decompose by desorbing methyl radicals. In hydrogen, the CH 3 radicals react with H 2 to form CH 4, whereas in helium, the CH 3 radicals recombine into C 2H 6. The growth rate decreases on switching from H 2 to He because of the change in film morphology. Evidently, the rougher films produced in helium contain fewer or less active sites for adsorption and decomposition of the organometallic molecules.