Impact Ionization Coefficients in (Al _x Ga_1-x )_0.52In_0.48P and Al _x Ga_1-x As Lattice-Matched to GaAs

Abstract

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.

Anomalous excess noise behavior in thick Al0.85Ga0.15As0.56Sb0.44 avalanche photodiodes

“…The small β / α ratio in thick avalanching materials containing Sb has been attributed to a suppression of the hole impact ionization, caused by the increased spin–orbit splitting energy in the valence band due to the presence of a large group V atom 26 . It may also be related to its indirect band gap and large difference between the Γ and X energy gaps at this high aluminium alloy composition as observed in the Al x Ga 1−x As and (Al x Ga 1−x ) 0.52 In 0.48 P 27 material systems. However, the excess noise measured in this work is significantly lower (by about five times) than what would be expected due to the β / α ratio alone.…”