Hydrostatic-pressure coefficient of the direct band-gap energy of AlxGa1-xAs for x=0-0.35

We have determined the pressure coefficient of the direct band-gap energy of AlxGa1-xAs (0 less than or equal to x less than or equal to 0.35), by measuring the photoluminescence and photoluminescence-excitation spectra of 200-Angstrom-wide AlxGa1-xAs/AlAs quantum wells with x values 0, 0.1, 0.18, 0.25, 0.3, and 0.35 at pressures up to 30 kbar. We have found that the pressure coefficient is independent of x within experimental uncertainties for x values in this range, clustering around 10.7 meV/kbar, a widely accepted value for bulk GaAs. This is in direct contrast to the only systematic measurement (at 300 K) in the literature, reported by Lifshitz er al. [Phys. Rev. B 20, 2398 (1979)], which showed a nonlinear, nonmonotonic dependence of the direct band-gap pressure coefficient on the x values. An explanation for this difference is offered.