Effect of pressure on the low-temperature exciton absorption in GaAs

We have measured low-temperature exciton optical-absorption spectra at the lowest direct band edge (E₀) of GaAs as a function of pressure up to 9 GPa. Spectra are analyzed in terms of the Elliott model by taking into account the broadening of the exciton line. In this way, we determine the dependence on pressure of the E₀ gap, the exciton binding energy scrR, and exciton linewidth at different temperatures. The pressure coefficient of the E₀ fundamental gap [107(4) meV/GPa] is found to be independent of temperature. The exciton binding energy increases with pressure at a rate of d lnscrR/dP=0.083(3) GPa^-1. The exciton lifetime becomes smaller for pressures above the crossover between {Γ}- and X-point conduction-band minima (P>4.2 GPa), a fact which is attributed to phonon-assisted intervalley scattering. From the pressure dependence of the exciton linewidth we determine an accurate value for the intervalley deformation-potential constant D_ΓX=4.8(3) eV/{}.