Low-voltage high-gain resonant-cavity avalanche photodiode

For p-i-n photodiodes and avalanche photodiodes (APDs) in the low-gain regime, there is a performance tradeoff between the transit-time contribution to the bandwidth and the quantum efficiency. A new photodetector structure is demonstrated that alleviates limitations imposed by this tradeoff. This structure utilizes a thin (about 900 A) depleted absorbing layer to reduce the transit time and achieve avalanche gain at low bias voltage (about 9 V). The external quantum efficiency has been enhanced (by over 49 percent) by incorporating the structure into a resonant cavity.