Development of low excess noise SWIR APDs

Abstract

There is a strong interest in developing sensitive Short Wavelength Infrared (SWIR) avalanche photodiodes (APDs) for applications like eye safe laser ranging and robotic vision. The excess noise associated with the avalanche process is critical in dictating the sensitivity of APDs. InGaAs APDs that are commonly used in the SWIR region have either InP or InAlAs as an avalanche layer and these materials have excess noise factor of 0.5 and 0.22, respectively. Earlier, Spectrolab had developed APDs with impact ionization engineering (I²E) structures based on InAlAs and InGaAlAs heterostructures as avalanche layers. These I²E APDs showed an excess noise factor of 0.15. A photoreceiver based on the I²E APD exhibited an noise equivalent power (NEP) of 150 fW/rt(Hz) over 1 GHz bandwidth at 1.06 μm. In this paper, a new multiplier structure based on multiple stages of I²E is studied. The APDs show optical gains over 100 before device breakdown. The increased gain and low excess noise will improve the sensitivity of InGaAs APDs based photoreceivers.