LWIR multispectral quantum well infrared photodetectors

This paper reports new results on multi/hyper-spectral IR detectors based on GaAs/AlGaAs multiple quantum well (MQW) materials. The wavelength tuned quantum-well IR photodetectors are obtained by patterning three-dimensional diffractive resonant optical cavities into the MQW structures. Control of the peak wavelength within the absorption band of the MQW material is achieved by adjusting the optical cavity dimensions. This approach enables highly effective optical coupling into the MQW material, produces narrow spectral response, improved detector quantum efficiency (QE) and reduced dark currents. Results are reported on the performance of multispectral. detectors that are designed to operate in the 8-14 mum spectral band. Spectrally broadened MQW material absorption is achieved by engineering a triple coupled quantum well design that produces absorption bands with full width at half maximum (FWHM) of greater than or equal to 3 mum. Two back-to-back MQW stacks have been employed to achieve spectral coverage in the range of 8-14 mum. As many as 52 different detector designs were fabricated on a single chip with 32x64 pixels. The spectrally tuned multispectral detector arrays exhibit excellent spectral dispersion and spectral response FWHM as narrow as similar to0.4 mum at 8.5 mum peak wavelength. The detectors exhibit QE values in the range of 15-50%. The background limited detectivity measured at 40 K with a 295 K background and f/2.5 is in the range of (0.8-1.5)x10(11) cm-Hz(0.5)/W. These high performance QWIPs are the first multispectral detectors fabricated over the 8-14 mum wavelength band.