A two-stack, multi-color in _0.5Ga_0.5As/GaAs and InAs/GaAs quantum dot infrared photodetector for long wavelength infrared detection

A two-stack multi-color quantum dot infrared photodetector (QDIP) for detection in the 8-12 μm spectral window was introduced. The top stack was made up of 8 periods of In_0.5Ga_0.5As/GaAs QDs, and the second stack consists of 8 periods of InAs/GaAs QDs, and a 500 Å GaAs spacer was used for each period in both stacks. A photoresponse peak around 7.9-9.0 μm was observed for the top stack, while two additional peaks (i.e., 7.2 and 10.6 μm) were found for the bottom stack. Thermionic emission current and thermally assisted tunneling current were found to be the major dark current components. The normal incident responsivity was observed up to 130 K for the top stack, and 110 K for the bottom stack, with S/N > 1. At V_b = -0.8 V and T = 40 K, the BLIP detectivity D* _BLIP was found to be 4.52 × 10⁹ cm Hz ^1/2/W at λ_p = 8.4 μm in the top stack. At λ_b = -0.77 V and T = 40 K, the value of D* _BLIP was found to be 2.06 × 10⁹ cm Hz ^1/2/W at λ_p = 10.6 μm for the bottom stack.