Epitaxial Growth of GaN on Lattice-Matched Hafnium Substrates

Abstract

A method of producing epitaxial GaN on single-crystal Hf has been developed. The metal substrate is formed by a strain-anneal process yielding macroscopic (5-mm) grain sizes, followed by polishing, chemical etching, and Ar ion sputtering at elevated temperature in ultrahigh vacuum. The growth is conducted by plasma-assisted molecular beam epitaxy using an initial passivation layer deposited at low temperature and subsequent growth at 700 °C. The resulting films are in registry with the hep substrate lattice as observed by reflection high-energy electron diffraction during growth and verified by plan-view transmission electron microscopy. High-resolution x-ray rocking curve linewidths of the GaN and Hf [1012] peaks are as narrow as 900 and 180 arc seconds, respectively. The [0002] peak separation confirms the approximately 2.7% mismatch in the c axis spacing. Initial photo]uminescence observations at 20 K of a (donor-bound exciton) peak at 3.467 eV are consistent with the assumption of a nearly strain-free film resulting from the exact basal-plane lattice match and close thermal coefficient match between GaN and Hf.