High dynamics measurements of spectral response were carried out on quantum well infrared photodetectors
(QWIP). This experiment revealed the presence of spectral structures which were never observed hitherto. Electric field assisted tunneling and, more surprisingly, Van Hove singularities at the miniband edges, have been observed in the low and high energy parts of the QWIP
spectra, respectively. These experimental features motivated us to initiate a theoretical study of the absorption in a multiquantum well structure.