Optical study of Al0.4Ga0.6Sb/GaSb single quantum wells

Despite the recent upsurge in research on GaSb-based systems, only few syst ematic investigations have been performed on the fundamental optical and el ectronic properties of AlxGa1-xSb/GaSb quantum wells. For this reason we st udied a series of Al0.4Ga0.6Sb/GaSb single quantum wells, with well thickne sses ranging from 40 to 117 Angstrom, by reflectance (R) and photoreflectan ce (PR) in the 0.6 to 1.5 eV spectral range and at temperatures from 6 to 3 00 K. The structures were grown by molecular-beam epitaxy on (001) GaSb sub strates and structurally and compositionally characterized by photoluminesc ence, x-ray diffraction, and reflection high-energy electron diffraction. B oth R and PR spectra showed clear evidence of the structures associated wit h the transitions allowed between the nth heavy-(light-) hole subband and t he nth conduction subband for n = 1 and 2. Standard critical-point line sha pes fitted satisfactorily the PR structures, allowing accurate determinatio n of both transition energies and broadening parameters as functions of the well thickness. The transition energies were well fitted by a theoretical model based on the envelope-function scheme, thus giving reliable values fo r the two fit parameters, i.e., the band offset and the conduction-band non parabolicity.