Enhanced initial photocurrent caused by the multiplication process at punch-through voltage in InGaAs/InP avalanche photodiode with highly doped charge layer

The device characteristics of InGaAs/InP avalanche photodiodes (APDs) with different doping concentration in charge layer are investigated numerically. It is found that with increasing the impurity concentration in charge layer, the APDs’ gain factor at 0.95Vbr increases slowly first and then decreases rapidly. It is considered that for the moderately doped samples, the increased gain can be ascribed to the enhanced multiplied photocurrent by the higher electric field in the multiplication layer due to the increased impurity concentration in charge layer. However, for the samples with ultra-high doping concentration, the calculated avalanche gain decreases remarkably. This can be attributed to the appreciably increased initial photocurrents induced by the avalanche multiplication process at the punch-through voltage due to the enhanced electric field in the multiplication layer, which may be a possible physical mechanism responsible for the reduction of avalanche gain in the APDs with highly doped charge layer.