BURIED-MESA AVALANCHE PHOTODIODES

We have developed a low-cost buried-mesa avalanche photodiode (APD) pr imarily targeted for 2,5-Gb/s lightwave applications. These APD's are made by a simple batch process that produces a robust and reliable dev ice,vith potentially high yield and thus low cost. The entire base str ucture of our InGaAs-InP APD is grown in one epitaxial step and the re maining process consists of four simple steps including a mesa etch, o ne epitaxial overgrowth, isolation, and metallization. Buried-mesa APD 's fabricated in this way show high uniform gain that rises smoothly t o breakdown with increasing reverse bias. When biased to operate at a gain of 10, these unoptimized devices show dark current less than 20 n A, excess noise factor less than 5, and a 3-dB bandwidth of about 4 GH z, With a 1550-nm laser modulated at 2488 Mb/s, a maximum sensitivity of -32.7 dBm was obtained with an optical receiver using one such APD, without antireflection coatings. These APD's not only demonstrate exc ellent device characteristics but also high reliability under rigorous stress testing. No degradation was observed even after being biased n ear breakdown for over 2000 h at 200 degrees C.