GaAs MBE growth under Ga-rich conditions studied by RHEED intensity oscillations

Abstract

We report on the study of RHEED intensity oscillations observed during the MBE growth of GaAs performed under different conditions. We experimentally show that under Ga-rich, As-limited conditions the growth rate does not depend only on the As beam equivalent pressure, but it is determined also by the As availability on the surface and that it has different values when a Ga-rich surface liquid phase is being formed or exhausted on the solid GaAs. Under the assumption that the surface liquid phase may also incorporate As, we deduce that the surface liquid phase may act as a sink or a reservoir of As, thus affecting the growth rate. We develop a quantitative model which: (1) explains the experimental data, and (2) allows for the evaluation of the Ga mole fraction in the surface liquid phase. We conclude that the liquidus temperature of the surface liquid phase is approximately 2/3 of that of the bulk GaAs system. This result points to a relevant contribution of the surface energy to the free energy of the surface liquid phase.