A highly sensitive multi-element HgCdTe e-APD detector for IPDA lidar applications

A HgCdTe e-APD detector has been developed for lidar receivers one application of which is integrated path differential absorption lidar measurements of atmospheric trace gases such as CO2 and CH4. The HgCdTe APD offers a wide, visible to MWIR, spectral response, high dynamic range, substantially improved sensitivity, and an expected improvement in operational lifetime. A demonstration sensor-chip assembly consisting of a 4.3 μm cutoff HgCdTe 4x4 APD detector array with 80 μm pitch pixels and a custom CMOS readout integrated circuit was developed. One typical array demonstrated APD gain of 654 at 12 V with corresponding gain normalized dark currents ranging from 1.2 fA to 3.2 fA. The 4x4 detector system was characterized at 77K with a 1.55 μm wavelength, 1 μs wide, laser pulse. The measured unity gain detector photon conversion efficiency was 91.1%. At 11 V bias the mean measured APD gain at 77 K was 307.8 with σ/mean uniformity of 1.23%. The average, noise bandwidth normalized, system NEP was 1.04 fW/Hz with a σ/mean of 3.8%. The measured, electronics limited, bandwidth of 6.8 MHz was more than adequate for 1 μs pulse detection. The system demonstrated an NEP (3 MHz) of 0.4 fW/Hz at 12 V APD bias and a linear dynamic range close to 1000. A gain independent quantum limited SNR of 80% of full theoretical indicated a gain independent excess noise factor very close to 1.0 and the expected APD mode quantum efficiency.