Impact Ionization Coefficients in (Al_xGa_1-x)_0.52In_0.48P and Al_xGa_1-xAs Lattice-Matched to GaAs

The impact ionization characteristics of (Al _x Ga _1-x ) _0.52 In _0.48 P have been studied comprehensively across the full composition range. Electron and hole impact ionization coefficients ( α and β, respectively) have been extracted from avalanche multiplication and excess noise data for seven different compositions and compared to those of Al _x Ga _1-x As. While both α and β initially decrease gradually with increasing bandgap, a sharp decrease in β occurs in (Al _x Ga _1-x ) _0.52 In _0.48 P when x > 0.61, while α decreases only slightly. α and β decrease minimally with further increases in x and the breakdown voltage saturates. This behavior is broadly similar to that seen in Al _x Ga _1-x As, suggesting that it may be related to the details of the conduction band structure as it becomes increasingly indirect in both alloy systems.