Piezomodulation spectra are reported for ${\mathrm{Ga}}_{1-x}{\mathrm{Al}}_x\mathrm{Sb}$ alloys. $E_0$, $E_0+{\Delta }_0$, $E_1$, $E_1+{\Delta }_1$ direct transitions and the lowest indirect transitions are observed as a function of temperature and alloy composition. At room temperature, the direct-indirect crossover occurs at $x=0.4\mathrm{}\pm 0.02$. The bowing parameters for the $E_0$ and $E_1$ gaps are 0.69 and 0.28 eV, respectively, and that for $\Gamma \to X$ indirect transitions is 0.48 eV. The spin-orbit splittings ${\Delta }_0$ and ${\Delta }_1$ are found to vary linearly with composition. Between 100 and 300°K the temperature dependence of various gaps is found to be linear. The coefficient of temperature dependence varies nearly linearly with composition. Theoretical calculations of bowing are examined. It is concluded that uncertainties in the material parameters of the pure compounds are the main cause which makes theoretical prediction of bowing parameters and crossover compositions rather uncertain.

• Received 16 June 1975

DOI:https://doi.org/10.1103/PhysRevB.12.5846