Comparisons between dual-depletion-region and uni-travelling-carrier p-i-n photodetectors

Space-charge and thermal calculations are used to compare the performance of gigahertz-bandwidth, high-current p-i-n photodiodes utilising InGaAs absorbers and InGaAs/ InP drift layers. By varying the percentage of InGaAs and InP in the drift layer, comparisons can be made between traditional p-i-n photodiodes (100% InGaAs drift layer), dual-depletion region photodiodes (part InGaAs, part InP drift layer), and uni-travelling-carrier (100% InP drift layer) photodiodes. A local maximum in the maximum photocurrent occurs when a charge balance is present in the depletion layer. The results from space-charge and thermal calculations show that traditional p-i-n and dual-depletion region designs can potentially provide performance that exceeds that of the uni-travelling-carrier design. Charge compensation is proposed as a means of increasing the space-charge-limited photocurrent and for controlling the peak electric fields within the depletion region.