Van Hove singularities in intersubband transitions in multiquantum well photodetectors

Photocurrent spectra of quantum well infrared photodetector (QWIP) devices have been studied over more than three orders of magnitude, revealing features which have been largely overlooked before. Electric field assisted tunneling and, more surprisingly, Van Hove singularities at the miniband edges are shown to play an important role in the low and high energy parts of the QWIP photocurrent spectra, respectively. The photoresponse of QWIPs away from their peak responsivity is found to be non-negligible (>1% in the 3-5 μm for a 8-12 μm detector), which has to be taken into consideration when optimizing multispectral devices.