Arsenic coverage dependence of the angular distribution of secondary ions desorbed from the GaAs{001}(2×4) surface

Abstract

Morphology and growth mode of Al films deposited by chemical vapor deposition from dimethylethylamine alane on GaAs(001)2×4 surfaces J.In this paper, we present a study of structural changes which may occur as a function of surface composition within a single surface reconstruction. We examine in detail the GaAs{001}(2 X 4) surface by measuring the ion beam desorbed Ga t-ion angular distributions as a function of As coverage. The distributions of these ions, initiated by 3-ke V Ar + ion bombardment at normal incidence, are measured as a function of azimuthal and polar angles of ejection from the molecular-beam-epitaxy-grown (2 X 4) surface. The distributions display extreme anisotropy, indicative of a specific collision sequence which results from the covalent nature of the GaAs crystal. More subtle blocking and channeling effects are also found in the angular pattern which allow qualitative analysis of the (2 X 4) surface structure. These results agree with the currently accepted model of missing As dimers for this reconstruction, which appear as open channels parallel to the (011) direction on the surface. The As coverage of the (2 X 4 ) surface was modified by molecular beam deposition of either As or Ga. These results indicate structural variations within the range of As and Ga coverages which are considered to yield the (2 X 4) reconstruction. The excess Ga atoms appear to adsorb in the fourfold hollow sites on top of the As dimers and at least 0.25 monolayer of Ga can be deposited before the surface reconstructs to a (3 Xl) symmetry. It is proposed that this adsorbed Ga may destabilize the (2 X 4) surface by opening the dimers, and thus initiating the reconstruction. Excess As atoms appear to adsorb in the fourfold hollow sites of the open channels on the (2 X 4) surface. The As coverage of the (2 X 4) surface was also modified by ultrahigh vacuum annealing. Angle-resolved secondary ion distributions and reflection high-energy electron diffraction patterns indicate that the surface reconstructs. It is concluded that the use of molecular beam deposition to vary the surface As coverage may be more effective than the thermal desorption of As, from a prepared surface.

Atomic placement of Al on the GaAs {001}c(4×4)reconstruction determined by angle-resolved secondary-ion mass spectrometry

“…Each one of the scans shows a highly anisotropic distribution, typical of Ga ϩ ions from GaAs ͕001͖ surfaces. 35,36 These scans also show how the Ga ϩ ion distribution changes with changing Al coverage. The clean c(4ϫ4) distribution, shown in Fig.…”

“…Typically, narrow peaks have been observed in distributions from semiconductors because a major ejection mechanism is nearest-neighbor collision along the bond direction. 25,36 Broader distributions have been observed more frequently for metal systems in which the collision cascade is not dominated by such highly directional motion. [38][39][40] The wide Al ϩ distribution in Figs.…”

“…It has been shown in previous studies that the Si PES adequately, though only qualitatively, describes the angular distributions of GaAs and Al/GaAs systems because the desorption mechanisms are more dependent on atomic positions than on mass or chemical environments of the atoms in the lattice. 25,27,35,36,41,45 Three different Al adsorption sites on the c(4ϫ4) reconstruction, shown in Fig. 1, were modeled with MD calculations using a Si ͕001͖ c(4ϫ4) reconstruction to identify desorption patterns of adsorbate and surface atoms.…”

“…The equipment required to perform these angle-resolved SIMS experiments on GaAs ͕001͖ surfaces is inherently complex 35,36 and has been modified significantly since its inception. Samples were prepared in a commercial Riber 2300 MBE chamber that is lined with liquid N 2 shrouds, evacuated with a 500 l/s ion pump, a titanium sublimation pump, and a 3700 l/s cryogenic array pump.…”