Study of infrared photodetectors with wavelength extension mechanism

The III-V semiconductor heterostructure-based photodetectors have been studied extensively for infrared detection, from near-infrared (NIR) to far-infrared (FIR) region. Due to the mature material system, GaAs/AlxGa1-xAs heterostructures are attractive options for development of infrared detectors. The conventional rule of photodetection, λt=hc/Δ determines the wavelength threshold (λt) of spectral photoresponse, where Δ is the minimum energy gap of the material, or the interfacial energy gap of the heterostructure. In recent studies on the p-GaAs/AlxGa1-xAs heterostructure-based infrared photodetectors, spectral threshold limit due to Δ has been overcome owing to a detection mechanism arising from the hot-carrier effect driven extended wavelength photoresponse mechanism. It has been experimentally observed that a detector with a conventional spectral threshold of ∼3.1 μm shows an extended wavelength threshold of up to ∼68 μm. An important advantage of the wavelength extension mechanism is the lower dark current, which is determined by the designed Δ. Dark current fittings obtained from a 3D carrier drift model closely agree with experimentally measured dark current. A barrier energy offset (δEv) between AlxGa1-xAs barriers is found to be necessary for the spectral extension mechanism.