A mass spectrometric study of the decomposition of trymethylarsine (TMAs) with triethylgallium (TEGa)

The decomposition mechanisms of trimethylarsine (TMAs) with triethylgallium (TEGa) were studied using a sampling gas method with a mass spectrometer. When TEGa is present, the TMAs concentration starts to decrease at temperatures about 100°C lower than for TMAs alone. The TMAs concentration in the gas phase decreases simultaneously with TEGa decomposition. The rate constant of the TMAs concentration decrease is strongly affected by the TMAs/TEGa mole ratio. However, the TEGa decomposition rate is not affected by the TMAs/TEGa mole ratio. The TMAs concentration decrease is mostly due to the decomposition of the adduct between TMAs and TEGa. TMAs in the gas phase starts to decompose and generate methane at 400°C. However, some TMAs molecules probably adsorb on the reactor surface and/or are incorporated into the GaAs crystal as carbon. Between 340 and 450°C, the concentration of carbon in the TMAs adsorbed on the surface as TMAs and/or incorporated into GaAs as carbon atom is stable and keeps a constant concentration: the TMAs generates no methane.