Role of subband occupancy on electronic transport in quantum cascade detectors

A model of the electronic transport in a quantum cascade structure under weak illumination in a very large temperature range is proposed. In a previous work, a simple model was shown to provide an expression of the quantum cascade detector (QCD) resistance in a range of temperature from 90 to 200 K. It relied on the assumption of the existence of a single, common quasi-Fermi level in a cascade of subbands, implying that the cascade is treated as a single reservoir of electrons. The electronic transport was successfully described with the doping density as the only adjustable parameter. However, it failed to reproduce experimental data at high temperatures. Indeed, in the latter range of temperatures (typically T > 200 K) which is important for applications of QCDs, the transport inside a cascade of levels is governed by a specific resistance and a continuous potential distribution between subbands. A more sophisticated model including this local Fermi level description is developed in detail and compared to experimental data here. An excellent agreement is found between the calculated and measured resistance of the structure from 50 to 300 K, varying over typically eight orders of magnitude.