Far-infrared Gallium Nitride-based Quantum Cascade Laser

Abstract

Gallium nitride semiconductors are considered as optimal candidate materials for terahertz quantum cascade lasers to achieve room-temperature operation and to fill the terahertz frequency gap of 6-12 THz, owing to the large longitudinal optical phonon energy (90meV, >21THz) which is 3 times that of gallium arsenide. However, the inter-subband lasing signal from gallium nitride cannot be easily obtained, with limitations such as the lack of a reliable design prediction model and the consistent epitaxy of a thick superlattice. In this chapter, the non-equilibrium Green’s function model is introduced to study the various scatterings in gallium nitride-based quantum cascade lasers and subsequently to predict the optical gain at different terahertz frequencies. In addition, thick GaN/AlGaN superlattice structures were grown using both techniques of in-house low-pressure metalorganic chemical vapor deposition and radio-frequency plasma-assisted molecular beam epitaxy.