Mechanism of stabilization of zincblende GaN on hexagonal substrates: Insight gained from growth on ZrB2 (0001)

Abstract: Thin (∼25nm) zincblende GaN (111) epilayers have been grown on hexagonal ZrB2 (0001) 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 (111) can be preferentially nucleated on hexagonal substrates is discussed. [Copyright &y& Elsevier]