High-quality GaN films grown on chemical vapor-deposited graphene films

We report the growth of high-quality GaN films on large-size graphene films for visible light-emitting diodes (LEDs). The graphene films were synthesized by chemical vapor deposition and then transferred onto amorphous silica (SiO2) substrates that do not have an epitaxial relationship with GaN. Before growing the high-quality GaN thin films, ZnO nanowalls were grown on the graphene films as an intermediate layer. The structural and optical characteristics of the GaN films were investigated, and the films exhibited stimulated emission even at room temperature, a highly c-axis-oriented crystal structure, and a preferred in-plane orientation. Visible LEDs that emitted strong electroluminescence under room illumination were fabricated using the GaN thin films. Transparent light emitters are of considerable interest for lighting applications or as displays in flat screens or mobile phones. However, existing transparent light emitters made from organic materials typically do not have light-emission efficiencies that match those of conventional semiconductors. Gyu-Chul Yi and colleagues from Seoul National University have now constructed a system based on a glass-bound layer of the semiconductor gallium nitride — which has been grown on a layer of graphene - that offers a solution to this problem. Gallium nitride is well-known from its use in blue light-emitting diodes, but its growth on transparent substrates such as glass has been challenging due to surface mismatches at the atomic level. If graphene, an atomically thin sheet of carbon atoms, is used as a buffer on top of the glass the quality of the films increases markedly. This makes possible efficient light emission, promising applications for transparent displays made from semiconductors. We demonstrate the growth of high-quality GaN films with flat surface and uniform morphology on large-scale polycrystalline chemical vapor-deposited graphene films. The films exhibit stimulated emission even at room temperature, a highly c-axis-oriented crystal structure, and a preferred in-plane orientation. Furthermore, the GaN films grown on the graphene films can be used for fabrication of blue and green light-emitting diodes.