Electrically driven optical resonance of spherical ZnO whispering gallery mode microcavity

Spherical microcavities with low optical loss and high quality factor are attractive candidates for functional applications, including whispering gallery mode lasers, intracellular lasers, ultrasensitive biosensors, etc. In particular, electrically driven devices are beneficial for several applications such as optoelectronic integration. However, it is difficult to realize the electrically driven optoelectronic functions. In this study, the high-quality ZnO microspheres are fabricated by using a laser ablation method, and an excellent ultraviolet lasing system is achieved by optical pumping. Moreover, ultraviolet electroluminescence analysis demonstrates that ZnO microspheres are bonded to the p-GaN substrate. Furthermore, distinct resonant modes are obtained after inserting an appropriate AlN buffer layer at the n-ZnO/p-GaN interface. The optoelectronic behavior, charge carrier transportation, and recombination mechanism of the structure are systematically analyzed, and related interface modification, energy band alignment, and optical gain/loss contrast are also discussed. Overall, the results provide useful insights on further exploration of electrically pumped ZnO microsphere lasers.