PROBING THE MECHANISMS OF GROWTH OF GALLIUM-ARSENIDE BY METALORGANIC VAPOR-PHASE EPITAXY USING EXPERIMENTAL AND THEORETICAL-STUDIES OF DESIGNED PRECURSORS

Decomposition of o-CH3C6H4AsD2 in the gas phase at 600-1000-degrees-C produces toluenes with 0-3 D atoms in the methyl group. It is shown th at this cannot be accounted for by conventional mechanisms involving i nitial As-C bond cleavage or reductive elimination, but rather that th e first step is As-D bond cleavage and this is followed by reductive e limination of o-CH3C6H4D or H atom transfer to give o-HDAsC6H4CH2. whi ch abstracts D from an intact o-tolylarsine to give O-CH2DC6H4AsHD. Re petition of these steps can lead to multiple D incorporation. The free energies of activation for reductive elimination or multiple D incorp oration are found to be very similar. Theoretical studies on the decom position of (t)BuAsH2 show that the first step for decomposition can b e As-H bond cleavage to give (t)BuAsH. or loss of H-2 to (t)BuAs. (t)B uAsH. decomposes to (t)Bu. which abstracts H. from (t)BuAsH2 to give 2 -methylpropane or by beta-H abstraction to give 2-methylpropene. (t)Bu As, on the other hand only gives 2-methylpropene, via a beta-H abstrac tion mechanism. Measured effects of total reactor pressure on product distribution are modeled qualitatively. Hex-5-enylarsine also decompos es via initial As-H bond cleavage followed by reductive elimination of 1-hexene. However, it reacts in the liquid or solution phase with Me3 Ga to give the adduct. [Me3Ga.AsH2hex]. On heating, this loses methane to give first [Me2Ga.AsHhex]3 then [MeGa.Ashex]n. Finally, GaAs is pr oduced with the formation of methane and methylenecyclopentane. The la st product indicates a free radical mechanism involving cleavage of th e As-hex bond for the last step. In the gas phase at 600-degrees-C, Ga As is again formed but the major C6 product is 1-hexene. This is inter preted as meaning that the adduct, [Me3Ga.AsH2hex] is not formed in th e gas phase under growth conditions.