Room temperature polariton lasing in III-nitride microcavities, a comparison with blue GaN-based vertical cavity surface emitting lasers

The authors report on room temperature (RT) lasing action in two different types of nitride-based microcavities (MCs): vertical cavity surface emitting lasers (VCSELs) and polariton lasers which operate in the weak and in the strong coupling regime, respectively. Following a brief description of these two operating regimes, an analysis of lasing action at RT is reported for a crack-free planar VCSEL structure based on a bottom lattice-matched AlInN/GaN distributed Bragg reflector (DBR) and a top dielectric DBR. The cavity region, formed by n- and p-type GaN layers surrounding only three InGaN/GaN quantum wells, corresponds to a typical active region suitable for an electrically driven VCSEL. Processing issues of such planar VCSEL structures and electroluminescence characteristics of processed devices are also reported. Then, an alternative approach relying on the realization of coherent GaN-MC light sources based on the spontaneous decay of a macroscopic polariton population, the so-called polariton laser, is described. It is shown that this kind of devices could work at RT with a potentially much lower threshold current density than VCSELs as it does not necessitate reaching population inversion conditions. As for VCSELs, we demonstrate laser-like properties above threshold, i.e. an intense polarized emission and a strong spectral narrowing. Differences of polariton lasers with conventional lasers are also highlighted.