High performance QWIP FPAs for the 8-12 µm and 3-5 µm regimes

Quantum well infrared photodetectors (QWIPs) have evolved into a mature, GaAs-based III-V technology that enables us to realize large infrared detector arrays with excellent thermal and spatial resolution, low fixed-pattern noise, low 1/f noise, and high pixel operability at moderate cost. We present here the present status of our QWIP focal plane array (FPA) developments for the 8 - 12 µm long-wavelength infrared (LWIR) and 3 - 5 µm mid-wavelength infrared (MWIR) regimes. In the LWIR, we have realized several types of QWIP FPAs with array sizes from 256 x 256 to 640 x 512 pixels and with different active regions, giving rise to photoconductive and photovoltaic operation, respectively. Noise-equivalent temperature difference (NETD) values below 10 mK at 30 ms integration time and f/2 optics have been observed in the case of a photovoltaic 640 x 512 FPA with 24 µm pitch. Together with the 5.2 mK NETD achieved previously with an 256 x 256 FPA, this is the best NETD ever demonstrated in the LWIR spectral regime with any detector technology. We have also worked towards photoconductive LWIR QWIP FPAs that show good NETD at very short integration times of 4 ms and below. For the MWIR, we have developed a GaAs-based 640 x 512 FPA comprising strained InGaAs/AlGaAs QWIPs. A high quantum efficiency of more than 10% in the long-wavelength part of the MWIR (4.4 - 5.1 µm) is achieved by increasing the carrier density and optimizing the geometry of the two-dimensional grating with 1.65 µm period. At 88 K detector temperature, 20 ms integration time, and f/1.5 optics, the MWIR QWIP camera shows an excellent NETD of 14.3 mK. Finally, we discuss the status of our ongoing development of a dual-band LWIR/MWIR QWIP FPA with 288 x 384 pixels and simultaneous detection of both bands in each pixel.