COUPLED GAS AND SURFACE-REACTIONS IN THE ORGANOMETALLIC VAPOR-PHASE EPITAXY OF CADMIUM TELLURIDE

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 CH3 radicals react with H-2 to form CH4, Whereas in helium, the CH3 radicals recombine into C2H6. 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.