A unified figure of merit for interband and intersubband cascade devices

By exploring a semi-empirical model, the saturation current density J(0) is identified to manifest the significant difference in carrier lifetime between interband cascade devices (ICDs) and intersubband quantum cascade devices (QCDs). Based on this model, the values of J(0) have been extracted for a large number of ICDs and QCDs from their current-voltage characteristics at room temperature. By analyzing and comparing available ICD and QCD data, we demonstrate how J(0) can be used as a unified figure of merit to evaluate both interband and intersubband cascade configurations for their device functionality. The significance of J(0) on the performances of mid-infrared detectors and photovoltaic cells is illustrated by comparing the measured detectivity (D*) and the estimated open-circuit voltage (V-oc) respectively. From extracted values of J(0), which are more than one order of magnitude lower in ICDs than that in QCDs with similar transition energies in active regions, and discussion of the consequences on device performance, the advantages of interband cascade configurations over intersubband quantum cascade configurations have been clearly revealed based on the same framework. The overall picture for both QCDs and ICDs sheds light from the perspective of a united figure of merit, which will provide useful guidance and stimulation to the future development of both ICDs and QCDs.