C-QWIPs for space exploration

We have extended our investigation of corrugated quantum well infrared photodetector focal plane arrays (C-QWIP FPAs) into the far infrared regime. Specifically, we are developing the detectors for the thermal infrared sensor (TIRS) used in the NASA Landsat Data Continuity Mission. This mission requires infrared detection cutoff at 12.5 μm and FPAs operated at ∼43 K. To maintain a low dark current in these extended wavelengths, we adopted a low doping density of 0.6 × 1018 cm−3 and a bound-to-bound state detector in one of the designs. The internal absorption quantum efficiency η is calculated to be 25.4% for a pixel pitch of 25 μm and 60 periods of QWs. With a pixel fill factor of 80% and a substrate transmission of 70.9%, the external η is 14.4%. To yield the theoretical conversion efficiency CE, the photoconductive gain was measured and is 0.25 at 5 V, from which CE is predicted to be 3.6%. This value is in agreement with the 3.5% from the FPA measurement. Meanwhile, the dark current is measured to be 2.1 × 10−6 A/cm2 at 43 K. For regular infrared imaging above 8 μm, the FPA will have a noise equivalent temperature difference (NETD) of 16 mK at 2 ms integration time in the presence of 260 read noise electrons, and it increases to 22 mK at 51 K. The highest operability of the tested FPAs is 99.967%. With the CE agreement, we project the FPA performance in the far infrared regime up to 30-μm cutoff, which will be useful for the Jupiter-Europa deep space exploration. In this work, we also investigated the C-QWIP optical coupling when the detector substrate is thinned.