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An ultralow dark current normal incidence p-type strained-layer In0.3Ga0.7Al/In0.52Al0.48As quantum well infrared photodetector (PSL-QWIP) grown on (100) semi-insulating InP substrate by molecular beam epitaxy technique for 8–12 μm infrared detection was demonstrated for the first time. This PSL-QWIP shows background limited performance (BLIP) for T≤100 K, which is the highest BLIP temperature ever reported for a QWIP. Due to a 1.5% lattice mismatch between the substrate and quantum well, a biaxial tensile strain was created in the In0.3Ga0.7As well layers. As a result, the light-hole state becomes the ground state for the free hole with small effective mass. The dramatic increase of optical absorption can be attributed to the large in-plane density of states and the small light-hole effective mass as a result of heavy- and light-hole state inversion. The dark current density and BLIP detectivity for this PSL-QWIP were found to be 7×10−8 A/cm2 and 5.9×1010 cm−√Hz/W, respectively, at λp=8.1 μm, Vb=2 V, and T=77 K.

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Investigation of a InGaAs/AlGaAs/GaAs p-type step bound-to-miniband compressively strained layer quantum well infrared photodetector grown on (100) semi-insulating GaAs has been made. A long wavelength infrared detection peak at 10.4 μm with a full width at half-maximum bandwidth, Δλ/λp=20% was obtained for this detector. The measured spectral peak is in good agreement with our theoretical prediction. A responsivity of 28 mA/W was obtained at T=65 K and V=3.0 V, with a spectral detectivity D* of 1.4×109 cm√Hz/W at T=65 K and V=1.0 V. The detector was under the background limited performance condition at T=40 K and V≤2.0 V.