Temperature-Programmed Scattering (TPS) Study on Reactivity Difference of GaAs and GaAs Oxide Surfaces

The reactivity of GaAs and GaAs oxide surfaces to trimethylgallium (TMG) was studied by temperature-programmed scattering (TPS) through the energy accommodation coefficient (EAC). The substrate temperature was increased at a constant rate while the scattered TMG was being measured under a constant flux of TMG supplied to the substrate by a cryo-shrouded quadrupole mass spectrometer. Since the detection efficiency of the spectrometer is inversely proportional to the translational velocity of scattered TMG, the observed intensity variation represents the change in translational velocity of reflected TMG during the temperature increase. The variation of the signal intensities was least-squares analyzed to yield the EAC, which is a measure of the surface reactivity. The thus-obtained reactivity of photo-oxidized GaAs to TMG is smaller than that of dark-oxidized GaAs, which is even smaller than that of a bare GaAs surface. This difference in the reactivity is discussed in relation to the mechanism of selective area growth of GaAs using GaAs oxide as a mask.