Ghulam Hasnain

In situ grown‐in selective contacts to n‐i‐p‐i doping superlattice crystals using molecular beam epitaxial growth through a shadow mask

Highly selective n‐ and p‐type contacts to GaAs doping superlattices have been achieved by using molecular beam epitaxial growth through a silicon shadow mask to form interdigital grown‐in contacts. Low contact resistance, excellent diode characteristics, and efficient lateral injection electroluminescence are obtained.

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 APDs 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/spl deg/C.

FREQUENCY DEPENDENT HOLE DIFFUSION IN INGAAS DOUBLE HETEROSTRUCTURES

Two‐dimensional diffusion of holes is studied in n‐type InGaAs heterostructures by frequency dependent measurements of the photoresponse in the periphery of a mesa diode. An analytical theory is presented that gives the spatial and frequency dependent photoresponse. Measurements agree well with theory and establish a hole diffusion length of 60 μm, a hole recombination lifetime of 3 μs, and a hole mobility of 480 cm2/V s for our material. An upper limit is also established for the recombination velocity at the InP or InGaAsP heterointerfaces.