STRAIN DEPENDENCE OF THE VALENCE-BAND OFFSET IN INAS/GAAS HETEROJUNCTIONS DETERMINED BY ULTRAVIOLET PHOTOELECTRON-SPECTROSCOPY

We have used ultraviolet photoelectron spectroscopy to study the strain dependence of the valence-band offset in situ for InAs/GaAs(100) heterojunctions grown by molecular-beam epitaxy. The Ga 3d(5/2) and In 4d(5/2) core-level to valence-band-maximum binding-energy separations and the Ga 3d(5/2) to In 4d(5/2) core-level energy separations were measured as functions of strain. This requires the growth of fully relaxed InxGa1-xAs buffer layers of varying composition as virtual substrates. We account for the true shape of the density of states near the valence-band edge by using results of k.p theory. Thus a full empirical pseudopotential calculation can be avoided. Our measurements yield valence-band offset values of 0.04+/-0.10 eV for InAs strained to GaAs(100), 0.57+/-0.10 eV for GaAs strained to InAs, and 0.36+/-0.06 eV for both strained to InP(100), respectively, the valence-band maximum being lower at the InAs side of the junction.