PRESSURE-DEPENDENCE OF THE INDIRECT BAND-GAP OF ALXGA1-XAS ALLOYS (X=0.70 AND 0.92) AT LOW-TEMPERATURES

We have measured photoluminescence and Raman spectra of liquid-phase-epitaxy-grown Al(x)Ga(1-x)As under hydrostatic pressure (0 < P < 6 GPa) at low temperatures (T < 10 K). The X-point exciton shifts with pressure to lower energies, for an aluminum concentration of x = 0.70 at a rate of -16.2(5) meV/GPa, for x = 0.92 at -16.5(5) meV/GPa. Taking into account the pressure dependence of the exciton binding energy, we determine the pressure shift of the indirect gap in these two alloys. For x = 1 (pure AlAs), an extrapolation leads to a rate of -15.3(5) meV/GPa for the indirect gap. Using this value, data on the pressure shift of the valence-band offset in GaAs/AlAs superlattices are reexamined. This shift approaches a value of 4.7 meV/GPa for large superlattice periods (> 20 monolayers).