Gain-bandwidth product analysis of InAlGaAs-InAlAs superlattice avalanche photodiodes

The gain-bandwidth (GB) product of InAlAs-InAlGaAs quaternary well superlattice avalanche photodiodes (SL-APD's) has been analyzed by solving current-continuity equations including electron and hole impact ionization rates in a separate absorption and multiplication (SAM) structure. The results indicate that the GB product of InAlGaAs quaternary well SL-APD's can be increased to more than 150 GHz by decreasing the thickness of a p(+)-InP field buffer layer. This is due to reduced ionization in the p(+)-InP field buffer layer, which has an opposite ionization rate ratio compared to the superlattice. This analysis was experimentally confirmed by a GB product of 150 GHz for the SL-APD's with a 33.4 nm thick p(+)-InP field buffer layer. The GB product obtained is the largest value in III-V compound-semiconductor APD's, to our knowledge.