Recent Advancements in HgCdTe APDs for Space Applications

Abstract

This work reports on recent advancements in the development of the Hg_1−xCd_xTe linear-mode, electron-initiated avalanche photodiode at Leonardo DRS. These detectors exhibit single-photon sensitivity from the visible to mid-wave infrared and have enabled several new NASA space LiDAR applications. In this paper, we first report on the issue of mitigating dark counts due to “ROIC glow.” By introducing a revised light-barrier in our detector design, we demonstrate a near factor of 4 reduction in glow-induced dark counts. We further present direct measurements of excess noise factor and describe post-analysis models that accurately extract this quantity from focal plane array performance data. All methods consistently reveal excess noise factors well below the McIntyre limit. Gain measurements are conducted on a smaller-format avalanche photodiode array and reveal gains of ~6100 (measured at a reverse bias of 14.9 V, operating temperature of 84 K and using a 1.55 µm illumination source), which is a new record for the mid-wave infrared technology at Leonardo DRS. Additional performance metrics such as false-event rate, photon-detection efficiency and timing jitter are presented for larger-format arrays (i.e. arrays with a greater number of pixels). We conclude with an examination of a non-fundamental, injection contact-induced breakdown phenomenon. Experimental data and modeling reveal that this breakdown is dependent on the gain and the photon signal level, and unrelated to classical avalanche breakdown.