Design concepts of terahertz quantum cascade lasers: Proposal for terahertz laser efficiency improvements

摘要

Conceptual disadvantages of typical resonant phonon terahertz quantum cascade lasers (THz-QCLs) are analyzed. Alternative designs and their combination within a concrete device proposal are discussed to improve the QCL performance. The improvements are ([1) indirect pumping of the upper laser level, (2) diagonal optical transitions, (3) complete electron thermalization, and (4) materials with low effective electron masses. The nonequilibrium Green's function method is applied to predict stationary electron transport and optical gain. The proposed THz-QCL shows a higher optical gain, a lower threshold current, and a higher operation temperature. Alloy disorder scattering can worsen the QCL performance.