Resonant effect and models of InP-based photodiode

In this paper, the frequency responses of InP/InGaAs vertical-incidence p-i-n photodiodes with various optical apertures of 50–80 μm are investigated. The same resonant frequency (fR) of approximately 1.02 GHz was observed for all device apertures. There are two conditions that can lead to the resonance of the frequency response. Therefore, an equivalent circuit model and a carrier transport model were used to fit and analyze the resonance curve. We then found that the resonant circuit can produce frequency response oscillations, but the peak position occurs at a higher frequency and the radio-frequency response drops more rapidly, which does not match the measured curve. Therefore, we believe that carrier transport delay is the main cause of the resonance. Based on the energy bands of our detectors and comparison with a reference device, it was found that when the blocked holes at the InGaAsP/InGaAs heterojunction interface tunnel through the potential barrier, a resonant frequency could be induced. Using our material structure and tunneling model, the tunneling frequency of the holes was calculated to be 0.99 GHz, which matched the measured resonant frequency value. Our resonant models provided two methods to improve the bandwidth for various photodetectors without any other change on the performance characteristics.