Impact Ionization Coefficients in (AlxGa1-x)0.52In0.48P and AlxGa1-xAs Lattice-Matched to GaAs

The impact ionization characteristics of (Al_xGa_1-x)_0.52In_0.48P have been studied comprehensively across the full composition range. Electron and hole impact ionization coefficients ( $\alpha $ and $\beta $ , respectively) have been extracted from avalanche multiplication and excess noise data for seven different compositions and compared to those of Al_xGa_1-xAs. While both $\alpha $ and $\beta $ initially decrease gradually with increasing bandgap, a sharp decrease in $\beta $ occurs in (Al_xGa_1-x)_0.52In_0.48P when ${x} > 0.61$ , while $\alpha $ decreases only slightly. $\alpha $ and $\beta $ decrease minimally with further increases in ${x}$ and the breakdown voltage saturates. This behavior is broadly similar to that seen in Al_xGa_1-xAs, suggesting that it may be related to the details of the conduction band structure as it becomes increasingly indirect in both alloy systems.