Spectral crosstalk by radiative recombination in sequential-mode, dual mid-wavelength infrared band HgCdTe detectors

Abstract

For small pixel, infrared (IR) focal plane arrays (FPAs), Raytheon Vision Systems’ architecture for integrated, dual-band detectors uses the sequential mode of the n-p+-n configuration. There is a single indium bump per pixel, leaving the p+ layer floating, and the operating polarity of the bias selects the spectral sensitivity by reverse-biasing the active p-n junction. Photogenerated minority carriers in the absorber layer of the forward-biased inactive photodiode are lost through recombination. This paper is the first report of a new optical crosstalk mechanism that occurs in sequential-mode, dual-band detectors. In the long-wavelength mode under out-of-band, short-wavelength illumination, radiative recombination yields emission near the bandgap energy of the short-wavelength absorber layer, resulting in a spurious short-wavelength response that appears as spectral crosstalk. We present experimental and device modeling results on the spectral crosstalk in molecular-beam-epitaxy-grown HgCdTe arrays with the cutoff wavelength of both bands in the 4–5-µm range.