Comparison between planar InP/lnGaAs/lnP pin photodiodes with symmetrical and asymmetrical doping profiles

High-speed p-end-illuminated planar InP/InGaAs/InP heterojunction p-i-n photodiodes have been fabricated with symmetrical and asymmetrical doping profiles. Static and dynamic characteristics of both devices were measured for comparison. The device with symmetrical doping profile exhibits inferior characteristics at low reverse bias (<4V). Nevertheless, if sufficiently reverse biased (>4V), a symmetrically doped device can have DC responsivity comparable to, and maximum 3 dB bandwidth higher than, a conventional asymmetrically doped device. The inferior characteristics at low reverse bias and promoted maximum bandwidth of a symmetrically doped device can be, respectively, attributed to the heterointerface exposed in the depletion region and reduced device capacitance caused by an extra-depleted InP region.