QUANTITATIVE ARXPS DEPTH PROFILING CHARACTERIZATION OF NATIVE OXIDES GROWN ON IN0.53GA0.47AS(100) SINGLE-CRYSTALS

We report the results of an angle-resolved X-ray photoelectron spectroscopy (ARXPS) quantitative study of room-temperature native oxides on LPE grown In0.53Ga0.47As(100). ARXPS is a powerful non-destructive experimental technique for identifying chemical species and following compositional variations close to the surface (less than 100 angstrom of thickness). Such investigations can be of relevance for understanding the growth mechanism, competition between different cations with respect to oxidation, and surface damage due to the degradation process. In this approach a model of photoemission from a planar InGaAs bulk covered with two homogeneous overlayers (representing an oxide and a degradation region) constitutes the basis of the computer-aided ARXPS analysis. The thickness and the composition of the two overlayers are the parameters of a curve fitting, based on the Laplace transform of step-like profile functions, of the experimental data taken at different photoelectron escape angles. Our results indicate the presence of non-stoichiometric oxides lacking oxygen with respect to In(OH)3, Ga2O3 and As2O3, respectively. An oxide layer about 9 angstrom thick is detected on the top of the original surface and is composed of 66% indium hydroxide, 31% arsenic oxide and 3% elemental arsenic. The following inner region corresponds to a diffuse interface oxide/substrate about 12 angstrom thick, containing 41% GaAs, 28% gallium oxide, 28% indium hydroxide and 3% InAs. Finally, the composition of the substrate agrees with the nominal composition of the epitaxially grown crystal. These results indicate a preferential oxidation of InAs with respect to GaAs and suggests that the driving force of the oxidation process is the binding energy difference of the two binary compounds constituting the crystal.