Inverse bandstructure engineering of alternative barrier materials for InGaAs-based terahertz quantum cascade lasers

Quantum cascade lasers (QCLs) are compact and powerful sources that cover a wide spectral range from infrared to terahertz (THz) radiation. The emission characteristics of QCLs depend on design parameters such as layer thickness, material composition and doping. Therefore, the material system has to be chosen accurately. Most commonly used material systems for THz QCLs are GaAs/AlGaAs and InGaAs/InAlAs. The latter requires very thin layers of InAlAs and is therefore difficult to manufacture epitaxially [1]. One solution to overcome this issue, while still making use of the benefits provided by InGaAs, namely lower effective electron mass (m∗= 0.043m 0 ) which leads to a higher optical gain, is the usage of different barrier materials such as the ternary GaAsSb [2] and the quaternary InAlGaAs [3]. Crucial for the barrier thickness is the conduction band offset (CBO) of the material system. The common notion is to employ barrier materials having lower CBOs and therefore thicker barriers.