Room-temperature stimulated emission of ZnO: Alternatives to excitonic lasing

ZnO is a wide gap semiconductor which has possible applications in blue light emitting diodes and lasers, devices, which are currently based on GaN. One advantage of ZnO compared to GaN is the much higher exciton binding energy of 60 meV compared to 26 meV in GaN. Due to this exciton binding energy many authors ascribe stimulated emission at room temperature (RT) to excitonic processes with presumably very low thresholds. In this contribution we investigate the temperature dependence of the band gap and of the homogeneous width of the free exciton resonance. Together with new and previous calculations and experimental data, these findings cast some doubt on the above claim and we present alternative interpretations for RT stimulated emission in ZnO.