Characterization of band gap in GaAsSb/GaAs heterojunction and band alignment in GaAsSb/GaAs multiple quantum wells

Photoreflectance (PR) and photoluminescence (PL) spectra are used to investigate the band alignment of GaAsSb/GaAs multiple quantum wells (MQWs). PR and PL spectra are measured for strained and unstrained GaAs1−xSbx/GaAs heterojunctions and coherently strained MQWs grown on a GaAs substrate by molecular beam epitaxy. The band gaps of the unstrained GaAs1−xSbx obtained from PL agree well with Eg(x) = 1.43 − 1.9x + 1.2x2. For the strained heterojunctions, the strain relaxation factor and the Sb mole fraction determined from PR measurements correspond to the results from X-ray diffraction. In the MQWs, the thickness of the GaAsSb layer is less than its critical thickness so the GaAsSb layer is coherently strained and the band gaps of the GaAs1−xSbx layers are estimated under this condition. In this study, the indirect transition from the electron levels in the GaAs layer to the hole levels in the GaAsSb layer is smaller than the band gap of the GaAsSb layer in the MQWs indicating that the band alignment of coherently strained GaAs1−xSbx/GaAs MQWs must be type-II.