The determination of the band offsets in strained-layer InxGa1-xAs/GaAs quantum wells by low-temperature modulation spectroscopy

We report a determination of the conduction-band offset ratio O c of the In x Ga 1-x As/GaAs strained-layer single quantum wells by low-temperature modulation spectroscopy. Various modulation reflectance measurements include contactless electroreflectance (CER), photoreflectance (PR) and piezoreflectance (PZR) are carried out on four different samples at room temperature and 20 K. The samples have In composition x=0.05 (sample A), 0.11 (sample B), 0.14 (sample C) and 0.21 (sample D) respectively. A number of allowed and forbidden excitonic transitions have been observed. The light-hole transitions were unambiguously identified by comparing the CER spectra with different modulation strengths. The origins of the various spectral features have been assigned by comparison with an envelope-function calculation taking into account the effects of strain. Good agreement between experiments and theory is achieved by taking Q c =0.46+or-0.05, 0.50+or-0.10, 0.54+or-0.07 and 0.63+or-0.05 for samples A, B, C and D respectively. It has been shown that O c depends linearly with the In composition x between 0.05 and 0.21.