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 3${\mathit{d}}_{5/2}$ and In 4${\mathit{d}}_{5/2}$ core-level to valence-band-maximum binding-energy separations and the Ga 3${\mathit{d}}_{5/2}$ to In 4${\mathit{d}}_{5/2}$ core-level energy separations were measured as functions of strain. This requires the growth of fully relaxed ${\mathrm{In}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As 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.