Growth and characterization of GaN on sapphire (0001) using plasma-assisted ionized source beam epitaxy

Abstract

A new approach to expitaxial GaN growth using the plasma-assisted ionized source beam epitaxy (PAISBE) is described. To facilitate the growth of GaN, an accelerated partially ionized Ga source beam was used along with an atomic nitrogen beam from an rf-discharge nitrogen plasma. To control the amount of N+2 ions leaving the discharge tube (thus participating in the GaN growth), a grid was installed at the exit end of the plasma tube. The growth parameters under control were the power and frequency of the rf discharge, the energy and fraction of ionization of the Ga beam, the Ga and N fluxes, and the substrate temperature. The crystal quality and surface morphology of the PAISBE-grown GaN films on sapphire (0001) were analyzed using reflection high-energy electron diffraction, x-ray diffraction, and scanning electron microscopy. The best films were obtained with a partially ionized Ga beam at an rf power of 140 W, which exhibited a full width at half maximum of 25 min at the (0002) diffraction peak for a 0.4-μm-thick film. The buffer layer was a GaN film grown at 400 °C. Results illustrating the effects of various control parameters and, in particular, those demonstrating the advantages of PAISBE are presented.