A systematic study of resonator quantum well infrared photodetector (QWIP)

We recently proposed a resonator structure to increase the quantum efficiency (QE) of a quantum well infrared photodetector (QWIP). In this detector systematic parameter study, we have selected two active layer thicknesses, three detector sizes, and three doping levels to investigate the Resonator-QWIP characteristics and the EM modeling in a wide range of detector parameters. To achieve the expected performances, the detector geometry must be produced in precise specification. In particular, the height of the diffractive elements (DE) and the thickness of the active resonator must be uniformly and accurately realized to within 0.05 μm accuracy and the substrates of the detectors have to be removed totally to prevent the escape of unabsorbed light in the detectors. To attain these specifications, two optimized inductively coupled plasma (ICP) etching processes are developed to fabricate a number of test detectors. Due to submicron detector feature sizes and overlay tolerance, we use an ASML stepper instead of a contact mask aligner to pattern wafers. The highest QE we found in this study is 64% obtained from a less optimized 30 μm pitch detector with 1.0×1018 cm-3 doping. In generally, the experimental result agrees with the prediction from electromagnetic (EM) modeling, and the R-QWIPs are able to maintain a relatively constant QE as the pixel size shrinks to 6 μm. The present 6 μm pitch R-QWIP FPA can potentially achieve 20 mK NETD at F/1.2 and 12 ms integration time.