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 Δ${\mathit{E}}_{\mathit{V}}$[==${\mathit{E}}_{\mathit{V}}$(InAs)-${\mathit{E}}_{\mathit{V}}$(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 (∼0.7 eV) in this system.