OBSERVATION OF DIRECT AND PHONON-ASSISTED INDIRECT TRANSITIONS IN GAAS GAXAL1-XAS MULTIQUANTUM WELLS UNDER HYDROSTATIC-PRESSURE/

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