INTERFACE FORMATION BETWEEN LAYERED-COMPOUND GAS AND GAAS(111)A SURFACE

The thermal evaporation of a GaS single crystal has been used for the first time to passivate the GaAs surface. The interface formation in t he initial stage of the growth of GaS on a GaAs(lll)A surface has been studied by low-energy electron-loss spectroscopy (LEELS), X-ray photo emission spectroscopy (XPS), and atomic force microscopy (AFM) as a fu nction of deposition temperature. Photoluminescence (PL) measurements of GaAs(lll)A with and without GaS thin films have also been carried o ut at low temperature (5.5 K) as a function of aging time in the atmos phere. The LEELS spectra shows that the surface-related peaks of GaAs disappeared immediately after starting the deposition, suggesting the effective passivation of dangling bonds of the GaAs surface by S atoms included in the evaporated species. The LEELS spectrum of the films g rown at 350 and 400 degrees C resembles that of a GaS single crystal, whereas that of the films grown at 450 degrees C and annealed at 500 d egrees C reveals that the GaAs surface was terminated by only an S lay er. LEELS and XPS spectra suggest that the crystal quality of GaS film s grown at 350 and 400 degrees C is improved by post-annealing at 450 degrees C. The band discontinuity between GaS and GaAs is estimated by XPS, and the results demonstrate a staggered-type band alignment. Sur face morphology of the films studied by AFM reveals the layer-by-layer initial growth of GaS. PL measurements suggest that the GaAs(111)A su rface is effectively passivated by a GaS films. (C) 1998 Elsevier Scie nce B.V. All rights reserved.