GROWTH OF AIN ON GAAS(110) BY REACTIVE MOLECULAR-BEAM DEPOSITION

AlN was synthesized by reaction of Al evaporated from a Knudsen cell with ammonia molecules on clean cleaved GaAs(110) surfaces at a growth temperature of 645 K. The chemical and electronic properties of the overlayers and interfaces were investigated by x-ray, soft x-ray, and UV photoelectron spectroscopy (UPS) and by means of low-energy electron energy-loss spectroscopy and the Kelvin method. With increasing AlN deposition the intensities of the Ga- and As-derived surface-state signals in the energy-loss and photoemission spectra, respectively, were found to decrease to the same extent and to have vanished for nominal coverages larger than 3 monolayers (ML). The intensities of the Ga(3d) and As(3d) core-level lines excited with Zr(M-zeta) radiation are reduced exponentially as a function of AlN coverage. The slope of this intensity decrease is smaller than the one observed for room temperature deposition. These findings indicate inhomogeneous growth of AlN at 645 K but abrupt interfaces. Photoemission data obtained with n- and p-type doped GaAs(110) indicate a pinning of the Fermi level at 0.51 eV above the top of the valence band for coverages larger than 3 ML. AlN thus induces surface states of donor and acceptor type which are attributed to a continuum of disorder-induced interface states. For nominal coverages larger than 3 ML the AlN valence-band structure dominates the UPS spectra. The valence-band discontinuity amounts to 2 eV.