Stimulated emission and lasing in whispering-gallery modes of GaN microdisk cavities

We report optically pumped, pulsed lasing action in whispering-gallery modes of GaN microdisk cavities at room temperature. The microdisk structure was fabricated by reactive-ion etching a 2-mu m-thick GaN epitaxial layer grown via metalorganic chemical vapor deposition. Below the lasing threshold, stimulated emission with superlinear pump-intensity dependence is observed. Spontaneous-to-stimulated emission transition occurs at a pump intensity that is 10x lower than that for a GaN sample without a cavity structure. Above the lasing threshold, the pump-intensity dependence is almost linear and gain pinning is observed. In addition, whispering-gallery modes are observed with the linewidth of individual peaks being as narrow as 0.1 nm. (C) 1999 American Institute of Physics. [S0003-6951(99)04028-0].