UV random lasing has been observed in highly disordered ZnO powders and polycrystalline films under optical excitation.[1, 2] However, because of i) insufficient optical gain and ii) difficulties in realizing highquality random media in ZnO-based heteroand homostructural p–i–n junctions, it seems technically challenging to fabricate UV ZnO random laser diodes.[3] Nevertheless, it is highly desirable to achieve lasing from ZnO random media under electrical excitation. This is because the use of random media will avoid the difficulty of cleaving smooth facets from the ZnO material in order to sustain lasing, leading to low-cost, high-volume fabrication of UV laser diodes.[2] Recently, we have demonstrated effective UV random lasing from patterned ZnO–SiO2 nanocomposite films under optical excitation. UV random lasing can be achieved in these films because the appropriate patterning of ZnO clusters enhances the optical quality (ie, higher gain and lower loss) of the random media.[4] Furthermore, the sandwiching of nanoparticles between the electron-and hole-injection layers has been shown to enhance the injection efficiency of the carriers so that the nanoparticles can attain a high optical gain under electrical excitation.[5, 6] Hence, if patterned ZnO–SiO2 nanocomposite films can be used as the intrinsic layer of ZnO-based heterostructural p–i–n junctions,[7] UV random lasing may be achieved. In this communication, we demonstrate for the first time the realization of random laser action in p-SiC (4H)/i-ZnO–SiO2 nanocomposite/n-ZnO: Al heterojunction laser diodes.

The schematic of the heterostructural p–i–n junction diode is shown in Figure 1. A p-doped single-side-polished 4H-SiC substrate (5 mm× 5 mm) is used as the hole-injection layer and an n-doped ZnO: Al (1%) layer of thickness ca. 250 nm is used as the electron-injection layer.[7] An intrinsic layer, which consists of ZnO powder embedded in a SiO2 matrix, is inserted between the n-and p-injection layers to form the p–i–n junction diode. The intrinsic layer is prepared by the sol–gel technique so that clusters of ZnO powder with a stripe