THE TEMPERATURE-DEPENDENT VARIATION OF BULK AND SURFACE-COMPOSITION OF INXGA1-XAS ON GAAS GROWN BY CHEMICAL BEAM EPITAXY STUDIED BY RHEED, X-RAY-DIFFRACTION AND XPS

The bulk as well as near-surface composition of InxGa1-xAs epilayers on GaAs grown by chemical beam epitaxy (CBE) has been investigated as a function of triethylindium (TEIn) flow rate and substrate temperature by reflection high energy electron diffraction (RHEED), X-ray diffraction, and X-ray photo electron spectroscopy (XPS). To clarify whether the bulk stoichiometry of CBE-grown ternaries can be extracted from the growth rate change as determined by the change in the period of RHEED oscillations from binary to ternary compound growth, a systematic study of growth rate change as a function of ternary bulk composition determined by X-ray diffraction has been performed at various temperatures. Our results show that for low growth temperatures there is a linear relationship between the two methods of determination, whereas no correlation is found for higher growth temperatures, in contrast to the MBE case where the two methods of determination give identical results. In the near surface region the epilayer composition is determined in situ by XPS. Using a new method for analysis of XPS spectra, where the ineiastically scattered electrons are taken into account, an extraction of quantitative depth information on the upper monolayers is possible. Our results show that In surface segregation is of minor importance at 470-degrees-C, but surface segregation of In occurs in InxGa1-x As at growth temperatures from 550 to 600-degrees-C. For samples grown at 550 and 600-degrees-C the surface In enrichment is not restricted to the upper monolayers, but extends to a depth greater-than-or-equal-to 50-75 angstrom.