High temperature adduct formation of trimethylgallium and ammonia

High temperature gas phase reactions between trimethylgallium (TMG) and ammonia were studied by means of in situ mass spectroscopy in an isothermal flow tube reactor. The temperature, pressure, and reaction time were chosen to emulate the gas phase environment typical of the metal-organic vapor phase epitaxy (MOVPE) of GaN. The main gas phase species is [(CH3)(2)Ga:NH2](x) where most probably x=3, resulting from the very fast adduct formation followed by elimination of methane. The further gas phase decomposition of this species proceeds through the stepwise elimination of methane. These studies indicate that little TMG exists within the growth ambient under most MOVPE growth conditions. The further gas phase reaction of [(CH3)(2)Ga:NH2](x) may be responsible for the strong dependence of the MOVPE GaN growth rate and uniformity commonly observed. (C) 1996 American Institute of Physics.