Oxygen adsorption and the surface electronic structure of GaAs (110)

The surface electronic structure of cleaved GaAs (110) is found to be very sensitive to small amounts of adsorbed oxygen. For example, adsorbing oxygen on only a few percent of the surface Ga or As atomic sites can produce changes of a factor of two in the surface electronic structure. Thus, long range effects must be involved, and these are associated with rearrangement of the surface atoms.     

Constant final state measurements of surface core-level binding energy shifts: InP(110) and GaAs(110)

The surface core-level binding energy shifts have been obtained for the In 4d and the P2p core-levels on the InP(110) surface. In agreement with previous studies of core-level shifts on the cleavage face of III–V semiconductors, the anion and cation shifts are of almost equal magnitude and are of opposite polarity (−0.31 and +0.30 eV respectively). The results are compared with a similar investigation of the GaAs(110) surface and discussed in terms of a recent calculation of surface core-level shifts for the (110) cleavage face of III–V semiconductors.     

On the electronic structure of cleaved GaAs(110) surfaces exposed to formic acid

GaAs(110) surfaces cleaved in UHV and exposed to HCOOH have been studied by work function measurements (Kelvin method), electron energy loss spectroscopy (ELS) and by low energy electron diffraction (LEED). From the different changes of the work function on n- and p-type material information about intrinsic and extrinsic surface states is derived. In the loss spectra the adsorbed formate species causes a loss near 9 eV. The intensity of the loss near 20 eV generally ascribed to an excitonic transition from the Ga 3d core level into surface states is reduced only by a factor of two after saturation with HCOOH. This might be related to the c(2 × 2) superstructure observed in LEED, which suggests a saturation coverage of half a monolayer.     

Application of high energy ion channeling to GaAs(110), Au-GaAs(110) and Pd-GaAs(110)

The first application of high energy ion channeling to the atomically clean GaAs(110) surface and metal-GaAs interfaces is reported. Questions of sample preparation, background correction and computer simulation are addressed. It is found that the Ga and As atoms at the clean surface are laterally displaced ? 0.1 Å from the ideal bulk-like sites. The implications of this result to current LEED models are discussed. Au overlayers, deposited at room temperature, do not seem to produce lateral displacements of the substrate for coverages below ≈ 5 monolayer (ML). However, ≈ 0.9 ML of the substrate are expanded or contracted upon Au deposition; this process is completed at a coverage of 0.5 ML. Neither an indication of any order in the Au film is found, nor seems a significant (? 5%) fraction of Au atoms to occupy substitutional sites. In contrast, room-temperature deposition of Pd disorders the substrate substantially, without threshold coverage, even at very small film thicknesses.