Photoresponse characteristics of uni-traveling-carrier photodiodes

Uni-traveling-carrier photodiode (UTC-PD) is a newly developed high-speed photodiode for generating high output current. The high saturation current is realized by its operation mode in which only electrons are used as active carriers. The bandwidth of a UTC-PD increases with increasing photocurrent level, which results from the fact that electron transport changes from diffusive to drift/diffusive motion due to the self-induced field in the absorption layer. In this report, photoresponse characteristics of InP/InGaAs UTC-PDs, which depend on device parameters and operation conditions, are discussed. Theoretical analysis for calculating 3-dB-down bandwidth as a function of operation current is also presented. The charge-control model for photodiodes, used in this study, allows us to predict small-signal bandwidth by numerical calculation.