Characteristics of AlN/Ni(111) Heterostructures and their Application to Epitaxial Growth of GaN

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We have demonstrated the first epitaxial growth of GaN on Ni(111) using low-temperature AlN buffer layers deposited by pulsed laser deposition (PLD). Reflection high-energy electron diffraction (RHEED) observations have revealed that the film quality of the AlN buffer layer strongly depends upon growth temperature. AlN buffer layers grown at substrate temperatures above 550 °C have shown ring RHEED patterns that are characteristic of polycrystalline films. In contrast, films grown at substrate temperatures lower than 450 °C have shown sharp, streaky RHEED patterns, indicating that the films grow epitaxially and are of a high quality. We have succeeded in preparing GaN films that show sharp, streaky RHEED patterns on AlN buffer layers grown at 450 °C. Grazing incidence-angle X-ray reflectivity (GIXR) and X-ray photoelectron spectroscopy measurements have revealed that the thicknesses of the intermixed layers at the AlN/Ni heterointerfaces decrease with decreasing growth temperature. These results suggest that AlN films grown at low temperatures by PLD serve as good barrier layers against the diffusion of Ni atoms, and allow us to obtain epitaxial GaN films even on chemically vulnerable Ni substrates.