Abstract
We present studies of GaAs/AlAs ultrashort-period superlattices grown on (In,Ga)As pseudosubstrates. Piezomodulation spectroscopy is used for the identification of conduction- and valence-band states involved in optical transitions. This study shows how the lattice mismatch between AlAs and (In,Ga)As can be exploited for the unconditional obtaining of pseudodirect GaAs/AlAs superlattices, with a ground conduction subband of Xz symmetry. It is shown that GaAs/AlAs superlattices, with ultrashort periods (2–8 monolayers), which are indirect when grown on GaAs substrate, become pseudodirect when grown on (In,Ga)As pseudosubstrate. In addition, the first quantized light-hole subband is found to be the ground valence-band state, in good agreement with envelope-function calculations including the coupling between light-hole and spin-orbit split-off bands.