Observation of direct and phonon-assisted indirect transitions in GaAs/GaxAl1-xAs multiquantum wells under hydrostatic pressure

Using photomodulated transmission spectroscopy we investigated the interband transitions in GaAs/Ga1-xAlxAs multiquantum wells as a function of hydrostatic pressure up to 50 kilobar. A number of spectral structures, associated with the Gamma, L, and X critical points in GaAs wells and Ga1-xAlxAs barriers were observed, and calculations were performed to help understanding their origins. The pressure coefficients of the direct transitions in the quantum wells fall between those of GaAs and Ga1-xAlxAs bulk. The observation of phonon-assisted indirect transitions is made easy by photomodulated transmission technique, and by the band folding effect in the multiple-quantum-well systems. The indirect transitions derived from the L conduction subbands and Gamma valence subbands have been observed in wide pressure ranges.