Tunneling effect on the intersubband optical absorption in quantum well structures

The tunneling effect on the intersubband optical absorption in a quantum well structure subjected to an external electric field perpendicular to the layers has been investigated theoretically. The analysis is based on the calculation of the intersubband transition rate by means of Fermi's golden rule using expressions for the density of states, and the wave functions of the quasi-stationary energy levels inside the quantum well obtained considering the tunneling of electrons. We find that the density of states consists of peaks with asymmetrical broadening, which increase with the electric field and their positions correspond to the quasistationary levels inside the quantum well, and an expression is obtained for the intersubband absorption coefficient as a function of the photon energy. We applied these results to calculate the responsivity spectrum for a multiple quantum well infrared photo-detector. The theoretical results are compared with experimental data.