Buried-mesa avalanche photodiodes

We have developed a low-cost buried-mesa avalanche photodiode (APD) primarily targeted for 2.5-Gb/s lightwave applications. These APDs are made by a simple batch process that produces a robust and reliable device with potentially high yield and thus low cost. The entire base structure of our InGaAs-InP APD is grown in one epitaxial step and the remaining process consists of four simple steps including a mesa etch, one epitaxial overgrowth, isolation, and metallization. Buried-mesa APDs fabricated in this way show high uniform gain that rises smoothly to breakdown with increasing reverse bias. When biased to operate at a gain of 10, these unoptimized devices show dark current less than 20 nA, excess noise factor less than 5, and a 3-dB bandwidth of about 4 GHz. With a 1550-nm laser modulated at 2488 Mb/s, a maximum sensitivity of -327 dBm was obtained with an optical receiver using one such APD, without antireflection coatings. These APD's not only demonstrate excellent device characteristics but also high reliability under rigorous stress testing. No degradation was observed even after being biased near breakdown for over 2000 h at 200°C