Room temperature ultraviolet lasing action in high-quality ZnO thin films

High-quality ZnO thin films were grown by plasma-enhanced molecular-beam epitaxy on sapphire substrates. In the edge emission geometry, lasing action has been demonstrated in ZnO thin films. The physical origin responsible for lasing action is discussed. The well-defined longitudinal modes could be observed, the mode spacing of 0.9 nm corresponds to a cavity of around 17.5 μm, and result from accidentally or naturally formed cavities. The lasing threshold was measured as a function of temperature, and the threshold was found to show weak temperature dependence.