Optical study of ${\mathrm{Al}}_{0.4}{\mathrm{Ga}}_{0.6}\mathrm{Sb}/\mathrm{GaSb}$ single quantum wells

Despite the recent upsurge in research on GaSb-based systems, only few systematic investigations have been performed on the fundamental optical and electronic properties of ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{Sb}/\mathrm{GaSb}$ quantum wells. For this reason we studied a series of ${\mathrm{Al}}_{0.4}{\mathrm{Ga}}_{0.6}\mathrm{Sb}/\mathrm{GaSb}$ single quantum wells, with well thicknesses ranging from 40 to $117\mathrm{\AA }$, by reflectance (R) and photoreflectance (PR) in the 0.6 to 1.5 eV spectral range and at temperatures from 6 to 300 K. The structures were grown by molecular-beam epitaxy on (001) GaSb substrates and structurally and compositionally characterized by photoluminescence, x-ray diffraction, and reflection high-energy electron diffraction. Both R and PR spectra showed clear evidence of the structures associated with the transitions allowed between the $n$th heavy-(light-) hole subband and the $n$th conduction subband for $n=1\mathrm{}$ and 2. Standard critical-point line shapes fitted satisfactorily the PR structures, allowing accurate determination 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 for the two fit parameters, i.e., the band offset and the conduction-band nonparabolicity.