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Photoresponse measurements were made to determine the compositional dependence of the Ga1−xAlxAs direct Γ15→Γ1 and indirect Γ15→X1 energy gaps. These data, together with other information, show that the crossover composition and energy gap are between 0.35xc0.40 and 1.87Egc1.97 eV, and that the most resonable values are 0.37 and 1.92 eV.
Casey et al. (Sat,) studied this question.