Ten years of QWIP development at Fraunhofer IAF

We report on our quantum well infrared photodetector (QWIP) developments aimed at high-performance thermal imaging with tow-dimensional focal plane arrays (FPA). Due to the limited charge storage capacity of today's readout circuits, high internal quantum efficiencies in combination with moderate responsivities and noise currents are desirable in order to optimize thermal resolution. Using FPAs comprising photoconductive QWIPs, very good noise-equivalent temperature differences better than 10 mK are obtained at small applied electric fields of 3 - 5 kV/cm. We also summarize the detection properties of photovoltaic "low-noise" QWIPs. In this novel device, the photoexcited-carrier mean free path corresponds to only one period of the active region and the noise associated with carrier capture is suppressed. Further improvement of the temperature resolution, in combination with an extremely large dynamic range, has been achieved using FPA cameras based on this detector concept. At present, QWIP FPAs achieve the best temperature resolution of any detector technology operating in the long-wavelength infrared atmospheric window.