STRAIN EFFECT ON BAND OFFSETS AT PSEUDOMORPHIC INAS/GAAS HETEROINTERFACES CHARACTERIZED BY X-RAY PHOTOEMISSION SPECTROSCOPY

We studied heterojunction band offsets at highly strained InAs/GaAs (100) heterointerfaces, using in situ x-ray photoemission spectroscopy with an emphasis on the effects of strain. Two extreme cases are examined: an InAs layer pseudomorphically grown on a GaAs substrate (type I); a GaAs layer grown on an InAs substrate (type II). It was found that the energy difference between In 4d and Ga 3d core levels in InAs/GaAs heterostructures depends only slightly on the in-plane lattice constant: 1.64 eV for type I and 1.60 eV for type II. However, the valence-band offsets DELTA-E(V)[=E(V)(InAs)-E(V)(GaAs)], which are deduced by theoretically taking into account the effects of strain on the core-level energies relative to the valence-band maxima as well as on a splitting of the valence-band maxima, are very different: 0.53 eV for type I and -0. 16 eV for type II. This clearly indicates a large effect of strain on the valence-band offset (approximately 0.7 eV) in this system.