Recent Progress in the Growth of Highly Reflective Nitride-Based Distributed Bragg Reflectors and Their Use in Microcavities

The growth of highly-reflective nitride-based distributed Bragg reflectors (DBRs) and their use in vertical cavity structures is reviewed. We discuss the various nitride material systems employed to design Bragg mirrors and microcavities, namely the Al_x(Ga)_1-xN/(Al)_yGa_1-yN and the lattice-matched Al_1-xIn_xN/GaN (x_In∼18%)-based systems. An emphasis on particular issues such as strain management, internal absorption, alloy morphology and contribution of leaky modes is carried out. Specific properties of the poorly known AlInN alloy such as the bandgap variation with In content close to lattice-matched conditions to GaN are reported. The superior optical quality of the lattice-matched AlInN/GaN system for the realization of nitride-based DBRs is demonstrated. The properties of nitride-based vertical cavity devices are also described. Forthcoming challenges such as the realization of electrically pumped vertical cavity surface emitting lasers and strongly coupled quantum microcavities are discussed as well, and in particular critical issues such as vertical current injection.