Indium arsenide electron avalanche photodiodes for femtowatt level infrared detection

Sensing of weak photon fluxes in the short to mid-wave infrared is important for a variety of applications such as optical communication systems, light detection and ranging (LiDAR) and remote gas sensing. For the most demanding applications, avalanche photodiodes (APDs) are regularly employed due to the enhanced sensitivity afforded by their internal avalanche gain. Indium Arsenide (InAs) is a material which exhibits near ideal avalanche multiplication properties and is capable of detecting infrared radiation up to 3 µm at 77 K. Due to exclusive multiplication of electrons, it exhibits incredibly low excess noise factors below 2, regardless of the magnitude of avalanche gain. Furthermore, unlike most APD technologies, its bandwidth is not limited by its avalanche gain, allowing it to operate at high speeds with high gains. Using our recently developed planar process, we report InAs avalanche photodiodes which exhibit high gains in excess of 100 and external quantum efficiencies at 1550 nm of 56 %. Our liquid nitrogen cooled detectors are combined with a low noise current amplifier and the performance of the system is analyzed. Detection of weak 1550 nm laser pulses corresponding to <70 photons per pulse is demonstrated. The detector's noise current is shown to be background limited, hence, detection of lower optical powers could be achieved through further set-up optimization.