SWIR nightglow radiation detection around room temperature with depletion-engineered HgCdTe on alternative substrates

Abstract

Night vision applications utilize the reflected nightglow radiation in the short-wavelength infrared (SWIR) atmospheric window. Nevertheless, the low light intensity values require dark current densities on the order of n A / c m 2 for detection around room temperature. Currently, with new device architectures and developments in growth and surface passivation, very low dark current density values are achievable for 1.7 µm cutoff InGaAs detectors near room temperature, and such detectors seem to be the leading choice for the nightglow detection applications. On the other hand, HgCdTe has not been thoroughly investigated for low-cost nightglow detection with 1.7 µm cutoff, primarily due to its manufacture expenses for lattice-matched CdZnTe growth. In this study, we analyze the nightglow radiation detecting performance of the alternative substrate HgCdTe detectors near room temperature ( T = 270 K ) using computer simulations. It is assessed that alternative substrate HgCdTe cannot attain the required dark current density values due to Shockley–Read–Hall (SRH) recombination in the depletion region, if the heterojunction photodiode structure is adopted. To overcome the problem, depletion-engineered devices are designed where the depletion region is embedded within a larger bandgap HgCdTe, which suppresses the depletion region SRH ∼ 1300 times. This reduces the dark current density to the desired order, for SRH lifetimes achievable with alternative substrate growth. Dark current densities as low as 0.26 n A / c m 2 are shown to be possible for an SRH lifetime of τ = 3 µ s while maintaining the quantum efficiency ∼ 85 % . With this approach benefiting from alternative substrates and depletion engineering, HgCdTe can achieve InGaAs nightglow imaging performances near room temperature, and can benefit from less costly manufacture and broader application capability for nightglow radiation detection.