Investigation of multicolor quantum well infrared photodetectors and type II superlattice infrared photodetectors

We developed two novel high-performance n-type quantum well infrared photodetectors (QWIPs) for 3--5 mum mid-wavelength infrared (MWIR), and 8--14 mum long-wavelength infrared (LWIR) detection. We simulated the InAs/GaInSb type II infrared photodetector to get optimal detector design and demonstrated InGaAsSb photodiodes using type II superlattice layers with different i layer thickness. For infrared imaging arrays, we also demonstrated two-color, two-stack QWIP 4 x 4 focal plane array (FPA) with dielectric grating and fabricated a 320 x 256 FPA test structure on the GaSb substrate.; First, an InGaAs/AlGaAs two-stack three-color QWIP for MWIR and LWIR dual band detection was presented. The LWIR TC-QWIP showed very high responsivity while MWIR BC-QWIP had very solid photosignal at up to 200 K. The second QWIP was a new high-sensitivity superlattice-coupled (SC) InGaAs/GaAs/AlGaAs QWIP. Excellent responsivity and detectivity due to the use of superlattice-coupled quantum wells were obtained and estimated, respectively.; We simulated an InAs/GaInSb type II IR detector for LWIR and VLWIR detection using two approaches: increasing the InSb mole fraction while keeping as = a∥ and increasing the thickness ratio of constituent layers for allowing small misfit. Through simulation we proposed optimal type II IR detector designs with large valence band splitting, thin superlattice layer and large absorption coefficients. Two high-detectivity InGaAsSb pin IR detectors were grown on the GaSb substrate with the modified i layer thickness. These detectors with type II superlattice window layer have excellent responsivity and detectivity regardless of the difference in i layer thickness.; Finally, two-color, two-stack QWIP 4 x 4 focal plane array (FPA) with dielectric grating were fabricated and characterized. Introducing dielectric grating as light coupling improved the performance of the 4 x 4 FPA with normal incident illumination. To test the feasibility of the larger format FPAs of GaSb based type II detectors, we fabricated a 320 x 256 FPA on GaSb substrate.