Quantum cascade laser gain medium modeling using a second-nearest-neighbor sp3s∗ tight-binding model

A ten-band sp3s∗ second-nearest-neighbor tight-binding model has been used to model the electronic structure of various AlxGa1−xAs quantum cascade laser gain media. The results of the calculations have been compared with experimental emission wavelength data, and it has been shown that the model predicts the photon energies at the peaks in the gain coefficient spectra agreeing, on average, to within 4 meV of the experimental values. Comparison of the results of the calculations with results from a two-band k→⋅p→ model shows that the tight-binding model is able to find the X-like states simultaneously with the Γ-like states. These X-like states were found to be strongly localized within the barriers. Finally, the model has also been applied to InAs/AlSb and InAs/AlSb/GaSb QCLs.