Low noise uncooled 2.0+µm APD for photon counting imaging and LIDAR applications

Abstract

State-of-art detectors having response over 2.0+ μm wavelengths require cryogenic coolers to improve SNR and achieve high sensitivity. Next generation detectors are required to operate at room temperature (300 K) to fit small form factor sensor modules for SWaP-efficient space instruments and defense applications. III-V materials-based p-i-n detectors (e.g. InGaAs) over 2.0+ μm wavelengths suffer from lattice mismatch with substrate, resulting in high dark currents, low sensitivity (low SNR), and needing cooling. An avalanche photodiode (APD) with high gain will significantly increase sensitivity above p-i-n detector solutions; however, dark current also multiplies under high gain, leading to increased noise. An APD’s material system dictates noise associated with gain process and depends on ratio of ionization coefficient (hereinafter mentioned as k or k-factor) which dictate the APD excess noise. In APDs, dark current and excess noise limit useful gain and hence the SNR of detection systems. Therefore, it is essential to reduce k-factor and dark current of an APD. We present a first in the world low-noise, high-gain, and high bandwidth 2.0+ μm uncooled APD having k factor of <0.01 enabling low excess noise at a given gain. The APD uses a novel structure and a bandstructure-engineered multiplication region based on III-V material system to reduce k-factor to near zero. We present the APD SACM device design, their simulations, and experimental results of fabricated APD devices. The uncooled 2.0+μm APD matches advantages offered by HgCdTe APDs having k~ zero, but with low dark currents at near room-temperature operation, and also mitigates both HgCdTe APDs and standard III-V p-i-n deficiencies to become an ideal solution benefiting to extend short-wave IR band to 2.0 +μm for imaging applications.