A study was made of GaN growth on Zn-polar ZnO substrates by using plasma-assisted molecular-beam epitaxy. Before GaN growth, ZnO substrate annealing conditions were optimized. Reflection high-energy electron diffraction patterns after low-temperature GaN buffer layer annealing changed from streaky to spotty, suggesting that Zn and O atoms interdiffused from the ZnO substrate into the GaN epilayer. This interdiffusion resulted in a mix-polar GaN epilayer.

Relation between Interdiffusion and Polarity for MBE Growth of GaN Epilayers on ZnO Substrates. Suzuki, T., Harada, C., Goto, H., Minegishi, T., Setiawan, A., Ko, H.J., Cho, M.W., Yao, T.: Current Applied Physics, 2004, 4[6], 643-6