Simultaneous reflection high-energy electron diffraction oscillations and mass spectroscopy investigations during molecular beam epitaxy growth of (001) GaAs - smooth surfaces or stoichiometric films?

Abstract

Film composition and surface morphology of molecular beam epitaxy (MBE)-grown GaAs(001) surfaces were investigated in situ as a function of flux ratio J Ga J As 4 . The flux of As 4 molecules desorbing from the sample surface was measured with a quadrupole mass spectrometer (QMS) simultaneously with the observation of reflection high energy electron diffraction (RHEED) intensity oscillations. The incorporation ratio, given by the number of incorporated Ga atoms per As atom, was calculated independent of both the QMS data and the decreasing growth rate for growth conditions with As deficiency, as obtained from the RHEED oscillation frequency. Stoichiometric growth was found up to a flux ratio J Ga J As 4 ≈ 0.9 . At flux ratios of 1.1 to 1.2, a minimum of the damping of the RHEED oscillation amplitude indicates a very smooth growth front profile, but Ga excess appears to be incorporated mainly in As sites without disturbing the crystal lattice. This assumption was confirmed by photoluminescence (PL) spectroscopy of films grown at a flux ratio J Ga J As 4 of 1.2. An additional PL peak was observed, which indicates the incorporation of Ga atoms on As sites.