Dependence of the direct and indirect gap of AlSb on hydrostatic pressure

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Abstract
The variation of the lowest direct and indirect absorption edges of AlSb with pressure has been measured at room temperature for pressures up to the phase transition at 7.9±0.2 GPa. Deviations from the simple indirect (square-root) absorption law are shown to be consistent at all pressures with a model which takes into account the variation of the energy denominators with photon energy. The analysis of the data provides accurate values for the indirect gap versus pressure and for the direct gap at zero pressure. The indirect gap varies linearly with pressure and sublinearly with lattice constant. These results are compared with predictions based on the empirical pseudopotential method. The calculated sublinearity of the direct and indirect gaps is nearly the same.