Ultraviolet lasing from ZnO single crystal at room temperature

We experimentally studied ultraviolet photoluminescence (PL) from ZnO (0001) single crystal at room temperature. The PL spectra taken from the sample edge show spectral width narrowing; lifetime shortening (100ps) and super linear intensity increase with pumping power, while the PL spectra taken from the sample surface only show broad spontaneous emission with a much longer lifetime (> 5 ns). These findings suggest that stimulated emission and lasing were only achieved at edges of the ZnO single crystal. Scanning-electron-microscopic images show a smooth sample surface morphology and a rougher morphology at the single crystal edge. Electron-hole plasma enhancement of gain may be attributed to the lasing effect observed from the sample edge.