Low temperature limits to molecular beam epitaxy of GaAs

We report reflection high-energy electron diffraction oscillations during molecular beam epitaxy of GaAs at temperatures as low as 125 °C using As2 as the arsenic source. At a substrate temperature of 200 °C, the As:Ga ratio is shown to be the critical parameter which determines the amplitude of these oscillations. The largest amplitude oscillations are obtained when the As:Ga ratio is about 1:1. In order for these oscillations to occur, the arriving atoms must have some surface mobility. Monte Carlo simulations show that step density oscillations with a period corresponding to one monolayer are expected if the incident atoms are allowed to move as little as one lattice site upon arrival at the surface.