Absorptive lasing mode suppression in ZnO nano- and microcavities

摘要

We conclusively explain the different lasing mode energies in ZnO nano- and microcavities observed by us and reported in literature. The limited penetration depth of usually used excitation lasers results in an inhomogeneous spatial gain region depending on the structure size and geometry. Hence, weakly or even nonexcited areas remain present after excitation, where modes are instantaneously suppressed by excitonic absorption. We compare the effects for ZnO microwires, nanowires, and tetrapod-like structures at room temperature and demonstrate that the corresponding mode selective effect is most pronounced for whispering-gallery modes in micro-wires with a hexagonal cross section. Furthermore, the absorptive lasing mode suppression will be demonstrated by correlating the spot size of the excitation laser and the lasing mode characteristic of a single ZnO nanowire.