InGaAs avalanche photodiodes optimized for eye-safe rangefinding applications

Design and performance characteristics of InGaAs/InP avalanche photodiodes which have been optimi7.ed for use in eye­ safe rangefinding applications are desaibed. The devices have diameters ranging from 85 to 350 µm. The use of a ball lens mounted on a bade-entry version of the 200 µm diameter APD Oextends its useful diameter up to 500 µm for most applications. For a 350 µm diameter APD, operating at 23°C, and biased to achieve a responsivity of 10 A/W at 1540 nm, typical dark current and noise are, respectively, 150 nA and 1.5 pA/lHz. In addition to room temperature performance characteristics, reduced noise and dark current at lower temperatures are reported for the various device types mounted on single stage thermoelectric coolers. In general, operation of the devices cooled also makes possible the use of higher gains - frequently as high as 2.5 - while still maintaining acceptable levels of noise and dark current. In particular, a typical 85 µm. diameter APD, operating at O"C, has noise less than 0.8 pA/./Hz when biased to operate at a 1540 nm responsivity of 20 A/W.