Reflection mass spectrometry of As incorporation during GaAs molecular beam epitaxy

An apertured and cryoshrouded mass spectrometer, which measures line-of-sight molecular fluxes from the surface, has been incorporated into a GaAs molecular beam epitaxy system. The spectrometer is simple to implement, yet is a powerful real-time growth diagnostic. We have used the spectrometer to measure transient and steady-state As incorporation from As4 during bilayer-by-bilayer growth of GaAs. We find, interestingly, that (1) the incorporation coefficient does not oscillate significantly; (2) transient incorporation coefficients depend on surface reconstruction, and may be higher than 0.5 at high Ga fluxes; and (3) in the absence of a Ga flux, excess Ga on the surface need not imply an incorporation coefficient of 0.5.