Nitride THz GaN quantum cascade lasers

The structural, material and field dependence of the THz lasing frequencies are reported for a QCL based upon GaN/AlGaN and GaN/InGaN heterostructures. The inter-subband transition initiated generation of THz followed by the LO-phonon assisted fast depopulation takes into account the appropriate energy band alignments. Valence and conduction band alignments incorporating spin-orbit and crystal field splitting as well as bi-axial strain are used to determine the conduction band offsets as a function of Al or In-mole fraction. We report the bias voltage, quantum well width and mole fraction dependence of lasing frequencies as well as their dependence on Ga or N-face growth. A lower THz frequency is predicted for Ga-face GaN/AlGaN-based QCLs using the revised energy band alignments. Ga-face QCL allows tunabilty of the generated THz radiation by varying the applied bias, whereas, N-face structures are insensitive to the variation of applied bias or current density.