Oxygen uptake during the MBE growth of AlxGa1−xAs epitaxial layers

This paper presents the results of a study of oxygen incorporation in Al_xGa_1-xAs epitaxial layers during MBE growth. Controlled, low levels of high purity oxygen have been introduced during growth and the structural properties of the layers measured by high resolution x-ray diffraction (HRXRD), while Secondary Ion Mass Spectrometry (SIMS) has been used to measure the oxygen content in the layers. The observations are interpreted by comparing these lattice parameter measurements with Al_xGa_1-xAs layers grown without admitting oxygen to the growth chamber. In the presence of oxygen, the Al_xGa_1-xAs lattice parameter exhibits contraction for Al fractions x up to 0.65 while layers with x fractions greater than 0.65 show an expansion in the Al_xGa_1-xAs lattice parameter. The x-fraction oxygen incorporation dependence, as well as the lattice parameter behavior, are accounted for by a model which discriminates between the propensities for O₂ to incorporate at As sites by (i) bonding to pairs of Ga atoms in the layer below, (ii) to pairs of Al atoms in the layer below or (iii) a combination of one Ga and one Al atom in the layer below.