Long-wavelength interband cascade infrared photodetectors operating above room temperature

We present recent studies on a set of three different long wave IR interband cascade infrared photodetectors with Type-II InAs/GaSb absorbers. Two of these detectors were two- and three-stage structures with regular-illumination configuration and the other was a two-stage structure with reverse-illumination configuration. The 100% cutoff wavelength for these detectors was 6.2 μm at 78 K and extended to 8 μm at 300 K. At T=125 K and higher temperatures we were able to observe the benefits of the three-stage detector over the two-stage device in terms of lower dark current and higher detectivity. We conjecture that the imperfections from the device growth and fabrication had a substantial effect on the low-temperature device performance and were responsible for unexpected behavior at these temperatures. We also found that the zero-bias photo-response increased for temperatures up to 200 K, which was indicative of efficient collection of photo-generated carriers at relatively high temperatures. Electroluminescence and X-ray diffraction measurements suggest that all three grown structures had comparable material qualities. However, the twostage detectors with the reverse-illumination had significantly lower performance than the other two detectors. The activation energy for the two-stage detectors with the reverse-illumination was 37 meV for T=78-100 K, which was much lower than the activation energies of the other two detectors (~140 meV). This low activation energy was attributed to shunt leakage observed in detectors with the reverse-illumination configuration.