Infrared detection utilizing both intersubband and free-carrier absorption in reverse-biased Superlattice infrared photodetector

Intersubband and free-carrier associated photoresponse in a GaAs-AlGaAs superlattice infrared photodetector is investigated. Under reverse bias, the photodetector is similar to an internal photoemission photodetector and significant photoresponse due to free-carrier absorption at the collector contact is found. In particular, in our photodetector, intersubband transitions at the superlattice layer also play an important role at low reverse biases and produce a photocurrent with an opposite direction to that of the free-carrier associated photocurrent. Since the total photocurrent consists of two components with opposite signs, photocurrent reversal occurs in the response spectrum. At high reverse bias, the intersubband-associated photoresponse is fully suppressed by the blocking barrier and the overall photoresponse is mainly due to the photoemission via free-carrier absorption at the collector contact. The intersubband and free-carrier associated photocurrent components under reverse bias can be resolved from the measured polarization dependence of the spectral response. The analysis of the measured free-carrier associated photocurrent agrees with previous studies on free-carrier absorption. A possible application with our detector to determine the wavelength of a monochromatic light is also demonstrated.