A generalized electron transport model in photodetectors for high-speed imaging

Photoelectron transport in a photodetector in an ultra-high frame rate image sensor under the uniform illumination condition is investigated. The charge readout time in a multi-implant photodetector is estimated using a generalized model with both diffusion equation and continuity equations. The maximum effective diffusion length was assigned to each implanted region after taking into account the fringing field drift due to multiple implants. Assuming that the charge on each section is directly proportional to its area under uniform illumination, the total charge transport as a function of time is obtained by the superposition of charge contribution of all implanted regions. By increasing the number of implants in the photodetector it may be possible to collect more than 10 million frames s^-1. The design effects are also investigated. The model showed excellent match with experimental results.