From GaN to ZnGa2O4 through a Low-Temperature Process: Nanotube and Heterostructure Arrays

We demonstrate a method to synthesize GaN ZnGa2O4 core shell nanowire and ZnGa2O4 nanotube arrays by a low-temperature hydrothermal process using GaN nanowires as templates. Transmission electron microscopy and X-ray photoelectron spectroscopy results show that a ZnGa2O4 shell forms on the surface of GaN nanowires and that the shell thickness is controlled by the time of the hydrothermal process and thus the concentration of Zn ions in the solution. Furthermore, ZnGa2O4 nanotube arrays were obtained by depleting the GaN core from GaN ZnGa2O4 core shell nanowire arrays during the reaction and subsequent etching with HCl. The GaN ZnGa2O4 core shell nanowires exhibit photoluminescence peaks centered at 2.60 and 2.90 eV attributed to the ZnGa2O4 shell, as well as peaks centered at 3.35 and 3.50 eV corresponding to the GaN core. We also demonstrate the synthesis of GaN ZnGa2O4 heterojunction nanowires by a selective formation process as a simple route toward development of heterojunction nanodevices for optoelectronic applications.