Mechanism of stabilization of zincblende GaN on hexagonal substrates: Insight gained from growth on ZrB2 (0Â 0Â 0Â 1)

Thin (∼25 nm) zincblende GaN (1 1 1) epilayers have been grown on hexagonal ZrB2 (0 0 0 1) substrates by plasma-assisted molecular-beam epitaxy at temperatures near 600 °C. Layers grown in near-stoichiometric conditions exhibit high phase purity; no wurtzite inclusions are detected by high-resolution X-ray diffraction or photoluminescence. For growth in the presence of excess Ga the layers are predominantly zincblende phase, but contain some wurtzite inclusions. Reducing the growth temperature to 400 °C results in a much-increased fraction of wurtzite inclusions. The growth of zincblende GaN with high phase purity on hexagonal ZrB2 implies the existence of an underlying physical mechanism rather than simply a result of “growth mistakes.” A possible surface energy-related mechanism by which zincblende GaN (1 1 1) can be preferentially nucleated on hexagonal substrates is discussed.