Suppression of excess noise in polarization enhanced back illuminated AlGaN solar-blind SAM APDs with modified multiplication layer

In this paper, we propose a novel and improved structure of a solar-blind back illuminated AlGaN separate absorption and multiplication avalanche photodiode (SAM APD) with a modified multiplication layer. It is shown that the excess noise factor can be suppressed at about 35% due to the higher threshold impact ionization energy of wide bandgap AlN layer inserted on both sides of the conventional avalanche layer. The enhanced polarization at the layer interface improves the photocurrent and the reduced excess noise limits the dark current. We use an in-house built simulator to investigate device characteristics of both the conventional and the proposed APDs. Some important figures of merit of the proposed solar-blind SAM APDs have been compared with the conventional ones and found to be superior in all aspects. With improved photocurrent, reduced dark current, low excess noise factor, excellent responsivity, and increased efficiency, the proposed device offers optimized solar-blind applications that can be useful in advanced optical fiber communication.