The reaction chemistry of cadmium telluride (CdTe) organometallic vapor-phase epitaxy (OMVPE) from dimethylcadrnium (DMCd), dimethyltelluride (DMTe), and diisopropyltelluride (DIPTE) has been studied by using on-line gas chromatography and numerical simulation. The organometallic compounds decompose on the CdTe surface by desorbing both alkyl radicals and hydrocarbon molecules. Gas-phase methyl radicals were detected by injecting ethylene, which reacted with the radicals and produced propane and other longer chain hydrocarbons. Methvi radicals from DMCD and hydrogen gas were found to be essential for DMTE decomposition. This suggests that H atoms, produced by the reaction of CH3* with H2, adsorb onto the CdTe and hydrogenate the methyl groups bound to Te sites. The large amount of ethane, isobutane 2,3- dimethylbutane, and propylene produced from DMCD and DIPTe decomposition in hydrogen indicates that a substantial fraction of the alkyl groups recombine and disproportionate on the semiconductor surface. In summary, this study has revealed that the deposition of CdTe from organometallic compounds occurs by a free-radical mechanism, which involves adsorption of the compounds, desorption of alkyl radicals, and the simultaneous hydrogenation, recombination, and disproportionation of alkyl species on the surface and in the gas phase.

back