Hydrothermally Grown Nonpolar a-Plane ZnO and Its Applications

Abstract

There has been great interest in ZnO as promising alternative light emitting material. It has wide direct bandgap of 3.37 eV and large exciton binding energy of 60 meV. A diverse of growth methods have been developed for ZnO epitaxial layer growth such as laser-assisted plasma enhanced chemical vapor deposition (PECVD), metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), and hydrothermal synthesis. Among them, hydrothermal growth is the cost-effective, environmentally friendly, and low thermal budget requiring process compared to conventional MOCVD. Most of hydrothermally grown ZnOs are in the shapes of nanorod or nanowire along c-axis due to fast growth rate of c-plane. Commercially available LEDs are based on GaN related material system, which is grown along the polar c-axis of wurtzite crystal structure. In this crystal, there exists spontaneous and piezoelectric polarization inducing internal electric fields which result in spatial separation of electron and hole wave functions. This quantum confined stark effect (QCSE) causes reduction in radiative recombination efficiency under high current injection. As one of solution, extensive efforts on nonpolar a-plane GaN are exerted. Nonpolar a-plane ZnO with high crystalline quality was successfully grown on a-plane GaN tempelate by simple, low-cost, and mass producible hydrothermal method. Synthesized a-plane ZnO thin film was studied with SEM, TEM, XRD, AFM, and PL analyses. In this presentation, growth of hydrothermal ZnO and its applications will be introduced.