A high strain two-stack, two-color, InGaAs/AlGaAs and AlGaAs/GaAs quantum well infrared photodetector for midwavelength infrared (MWIR) and long wavelength infrared (LWIR) detection has been demonstrated. Each stack is designed to have detection in one of the two atmospheric windows, 3–5 μm and 8–12 μm, respectively. The MWIR stack has employed 35% of indium in the InGaAs well, which not only achieved peak wavelength at 4.3 μm, but also obtained very high peak responsivity of Rp=0.65 A/W, using 45° light coupling. Normal incidence without grating coupling also has high responsivity with 40%–50% in the MWIR stack and 35%–45% in the LWIR stack, respectively, compared with the 45° incidence. Despite the large in-plane compressive strain induced by the high indium concentration, the device is highly uniform and has very low dark current in the MWIR stack. The background limited temperature is 125 K for the MWIR stack with a cutoff wavelength λc=4.6 μm, and is 70 K for the LWIR stack with λc=10 μm.

A voltage-tunable multicolor triple-coupled quantum-well infrared photodetector (TC-QWIP) has been developed for 8–12 μm detection. The TC-QWIP consists of three coupled quantum wells formed by an enlarged Si-doped InxGa1−xAs quantum well and two undoped GaAs quantum wells separated by two thin AlyGa1−yAs barriers. Two TC-QWIP structures with varying indium and aluminum compositions were designed and demonstrated. Due to the strong coupling effect of the asymmetrical quantum wells, three bound states (E1, E2, E3) are formed inside the quantum wells of the TC-QWIP. The main detection peak wavelength is due to E1→E3 bound states transition for both devices, while two secondary detection peaks due to E1→E2 and E1→Ec continuum states transitions under different biases were also observed. In addition, a strong quantum-confined Stark shift effect for the E1→E3 transition was observed in the wavelength range of 8.2–9.1 and 10.8–11.5 μm for QWIP-A and QWIP-B, respectively; both devices exhibit a linear dependence of detection peak wavelength on the applied bias voltage. A spectral responsivity of Ri=0.05 A/W and background limited performance (BLIP) detectivity DBLIP*=6.1×109 cm√Hz/W were obtained at Vb=5 V, λp=8.6 μm, and TBLIP=66 K for QWIP-A, while Ri=0.33 A/W and DBLIP* =1.63×1010 cm√Hz/W at Vb=4 V, λp=11.2 μm, and TBLIP=50 K were obtained for QWIP-B.

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