Frequency response and design consideration of GaN SAM avalanche photodiodes

In this work, a method is developed for estimating the frequency response characteristics of GaN avalanche photodiodes (APDs) with separated absorption and multiplication regions (SAM). The method calculates the total diode current with varying frequency by solving transport equations analytically and uses a commercial device simulator as a supplement for determining the exact electrical field profile within the device. Due to the high carrier saturation velocity of GaN, a high-gain-bandwidth product over THz is found achievable for GaN SAM-APDs. The potential performances of GaN SAM-APDs with different structural designs are further compared through numerical studies. It is found that a close-to-reach-through design is attractive for simultaneously achieving both relatively low operation voltage and high working frequency. In addition, transit-time limit and RC-delay limit for the frequency response of GaN SAM-APDs are also discussed.