Pressure dependence of the energy gap in some I-III-VI2compound semiconductors

The shifts in the absorption edge with hydrostatic pressure have been measured for four ternary semiconductors. In all cases the energy gap increases with pressure. From the data the pressure dependence of the energy gap ($\frac{d{E}_g}{dP}$) was determined as 2.2 meV/kbar for AgGa${\mathrm{S}}_2$, 3.4 meV/kbar for CuGa${\mathrm{S}}_2$, 5.3 meV/kbar for AgGa${\mathrm{Se}}_2$, and 2.7 meV/kbar for AgIn${\mathrm{Se}}_2$. These shifts are compared with the corresponding II-VI compounds and discussed. Some optical effects associated with the pressure-induced phase transitions in some of the ${\mathrm{I}-\mathrm{I}\mathrm{I}\mathrm{I}-\mathrm{V}\mathrm{I}}_2$ compounds and II-VI compounds are described and discussed.