Formation of random laser action in ZnO thin films

A review of recent work on random laser action in ZnO thin films is presented. Room-temperature ultraviolet lasing has been demonstrated in highly disordered ZnO film grown on (100) silicon substrate. The disordered gain media is achieved by post growth annealing of ZnO films and random arrays of ZnO nanorod embedded in ZnO epilayers. Irregular ZnO grains are found to occur through post-growth annealing of high-crystal-quality zinc oxide thin films and laser cavities are generated by closed-loop optical scattering from the lateral facets of the grains. In the case for ZnO nanorod arrays, the design of slab waveguide provides extra gain length and shorter scattering mean free path and leads to coherent random lasing. It is found that the lasing wavelength and linewidth of the zinc oxide random lasers under 355 nm optical excitation are around 390 nm and less than 0.4 nm, respectively. In addition, the dependence of the lasing threshold intensity on the excitation area has shown good agreement with the random laser theory.