MECHANISM OF GALLIUM-ARSENIDE MOCVD

There are many points to be elucidated as to the chemical reactions between TMG and AsH3. We have examined the vapor species in a MOCVD reactor by means of ir absorption spectroscopy and mass spectroscopy. The gas phase reaction of TMG with H2 occurs above 400°C, giving rise to Ga deposition and CH4 generation. On the other hand, the pyrolitic reaction of TMG takes place above 600°C in the absence of H2, leading to Ga deposition and the generation of CH4, C2H4, etc. In the mixture of TMG and AsH3, an unidentified species which corresponds to 2080 cm-1 absorption spectrum is detected. Mass spectroscopic analysis reveals that a complex of the 2080 cm-1 spectrum is AsH(CH3)2 or AsH2CH3. In the case of AsH3, AsH3 decomposes catalytically on the surfaces of GaAs crystals. The dependence of the decomposition rate on the orientation of the GaAs surface and the Ga melt has been studied. The catalytic effect is largest on the (111)A surface and decreased in the order of the Ga melt and the (100) surface. The catalytic effect is not observed on the (111)B surface. Namely, the catalytic reaction rates depend on the density of Ga-single bonds. It is likely that the final species adhered to the (111)A at the largest rate in MOCVD is GaAs. © 1990.