Intersubband (ISB) photodetectors are a suitable choice for the detection of light in the mid-infrared and terahertz regime. They are categorized into two main classes based on their working principle: photoconductive quantum well infrared photodetectors (QWIPs) and photovoltaic quantum cascade detectors (QCDs). Here, we focus on QCDs, which operate at zero bias and thus exhibit superior noise behavior due to the absence of dark current noise [1] . Lattice matched QCDs are based on the material system In 0.53 Ga 0.47 As/In 0.52 Al 0.48 As with a conduction band offset (CBO) of 520meV. The absorption in QCDs is based on the optical transition from the ground level g to the degenerate absorption levels a i in the active well. The detection wavelengths for lattice-matched QCDs are thus limited to values well above 4µm. Giorgetta et al. presented a short wavelength QCD at 4µm based on the strain compensated material system In 0.61 Ga 0.39 As/In 0.45 Al 0.55 As [2] . For this material system a CBO of 610meV is obtained by using model-solid theory [3] , [4] .     «

Intersubband (ISB) photodetectors are a suitable choice for the detection of light in the mid-infrared and terahertz regime. They are categorized into two main classes based on their working principle: photoconductive quantum well infrared photodetectors (QWIPs) and photovoltaic quantum cascade detectors (QCDs). Here, we focus on QCDs, which operate at zero bias and thus exhibit superior noise behavior due to the absence of dark current noise [1] . Lattice matched QCDs are based on the material...     »