Emission mechanisms in low-threshold UV random laser based on ZnO microrod array

Despite rather extensive study of the random lasing effect in ZnO structures, the issue of the optical gain mechanisms in microstructured ZnO random lasers remains poorly understood. In this work, the radiative properties of an array of vertically aligned ZnO microrods, synthesized by a modified thermal evaporation method, were studied. The microrods exhibited lengths up to 60 μm and diameters ranging from 1 to 5 μm. Random lasing from a microrod array was observed in the near-UV range (with a laser emission peak wavelength of ∼391 nm) with a threshold down to 40 kW/cm2 under optical excitation. An analysis of the nature of optical gain in the grown structure was conducted at various temperatures. It was found that at room temperature, two-phonon-assisted exciton recombination is the main process leading to light amplification.