Relation between interdiffusion and polarity for MBE growth of GaN epilayers on ZnO substrates

We report on GaN growth on Zn-polar ZnO substrates using plasma-assisted molecular-beam epitaxy (P-MBE). Before GaN growth, ZnO substrate annealing conditions were optimized. Reflection high-energy electron diffraction (RHEED) patterns after low-temperature GaN buffer layer annealing changed from streaky to spotty, suggesting that zinc and oxygen atoms interdiffuse from the ZnO substrate into the GaN epilayer. This interdiffusion results in a mix-polar GaN epilayer.