The observation, reported in Applied Physics Letters, changes scientists' understanding of solid-state lasers and suggests that these devices can be made much more simply than they have been. Semiconductor lasers, in which the light is reflected back and forth between the end facets of a crystal, have been made only by complicated techniques to grow near-perfect crystal films. The expense of fabrication has limited the range of applications for these tiny lasers, says Robert P.H. Chang, director of the Materials Research Center and one of three senior researchers on the study. Chang, professor of materials science and engineering in the Robert R. McCormick School of Engineering and Applied Science, with graduate student Hock Ong and visiting scholar Ji Dai, grew thin films of zinc oxide on ordinary glass wafers.
Zinc oxide is a semiconductor with a blue luminescence and a high optical gain to amplify light.
It has been used extensively in resistors and diodes. The powdered zinc oxide layer has a highly disordered structure. The researchers were able to show that this disorder paradoxically enhances the lasing effect. Traditional semiconductor lasers, with well-defined cavities, have perfectly ordered structures to minimize light scattering. In those devices, normal light scattering reduces laser output.