Quantum well infrared photodetectors for long wavelength infrared imaging applications

Long wavelength Quantum Well Infrared (QWIP) cameras developed at the Jet Laboratory demonstrate the potential of GaAs/Al_xGa _1-xAs QWIP technology for highly sensitive, low power, low cost, and highly uniform large format (focal plane array (FPA)) imaging systems. These cameras utilize FPAs as large as 640×486 based on optimized GaAs/AlGaAs multiquantum-well (MQW) structures coupled with random or two dimensional periodic grating reflectors. Reported uniformities of these FPAs are better than 99.95% after two point correction has been reported. Other advantages of GaAs/AlGaAs based QWIPs are higher yield, durability, radiation hardness, and no 1/f noise till 30 mHz. In addition, QWIPs offer greater flexibility than usual extrinsically doped semiconductor IR detectors because the wavelength of the peak response and cutoff can be continuously tailored by varying layer thickness (wellwidth,) barrier composition (barrier height), and carrier density (well doping density). The GaAs/Al_xGa_1-x As material system allows the quantum well parameters to be varied over a range wide enough to enable light detection at any wavelength range between, 6-20 μm. The spectral band width of these detectors can be tuned from narrow (Δλ/λ~10%) to wide (Δλ/λ ~40%), allowing various applications. Also, QWIP device parameters can be optimized to achieve extremely high performance at lower operating temperatures (~40 K) for low background, long-wavelength, infrared applications in the strategic arena as well as in astronomy