The authors have achieved directional coherent random lasing from p-GaN/i-ZnO-SiO_2 nanocomposite-ZnO heterojunction diodes. This is due to the use of relatively low refractive indexed carrier injection layers (i.e., cladding layers) and relatively high refractive indexed intrinsic layer with stripes of ZnO clusters (i.e., core layer) that allows the transverse confinement of in-plane closed-loop random cavities. Hence, directional lasing emission can be observed from the edge of the diodes. However, the choice of highly concentrated ZnO clusters, which is supposed to enhance the transverse confinement and optical gain, is not preferred for the fabrication of intrinsic layer. This is because the influence of corrugation effect (i.e., strong surface scattering) supersedes the transverse optical confinement of the diodes.
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