Fabrication of InGaAs/InP single-photon avalanche diodes for SWIR active imaging

Imaging LiDAR (light detection and ranging) systems for sensing the surrounding environment are a key component for, e.g., reconnaissance and autonomous navigation. The physical basis of LiDAR systems is the time-of-flight measurement of the backscattered intensity of a pulsed laser beam. For a sufficiently high detection efficiency, the highest possible sensitivity of the photodetector is required as provided by the single-photon avalanche diode (SPAD). The maximum detection range can be even further extended by the usage of laser sources for the short-wavelength infrared (SWIR) spectral range with typical wavelengths around 1550 nm, allowing for increased optical intensities to be emitted. The InGaAs/InP material system is ideally suited for SPADs for the SWIR spectral range. The fabrication of InGaAs/InP SPADs into focal plane arrays as core component for future imaging lidar systems with a high spatial resolution are quite demanding. The key technology for the fabrication of InGaAs/InP SPADs is the planar process technology via zinc diffusion to produce spatially confined p-type regions. For the zinc-diffusion process, a novel method of selective epitaxial overgrowth was developed, achieving the intended double-diffusion profile. First experimental data of thus fabricated InGaAs/InP avalanche photodiodes show the expected dark-current, photo-current, and multiplication-gain characteristics in linear-mode operating, as well as breakthrough behavior in Geiger-mode operation at typical operating temperatures around 220 to 240 K, which are achievable by thermoelectric cooling.