Growth of Ga- and N-polar GaN layers on O face ZnO substrates by molecular beam epitaxy

Publication date: 15 February 2014
Source:Journal of Crystal Growth, Volume 388
Author(s): Y. Xia , J. Brault , P. Vennéguès , M. Nemoz , M. Teisseire , M. Leroux , J.-M. Chauveau
Gallium nitride (GaN) epitaxial layers have been grown on O face $(000\overline{1})$ zinc oxide (ZnO) substrates by ammonia source molecular beam epitaxy. By adjusting the growth temperature and the III/V ratio during the nucleation stage, GaN layers with Ga $(0001)$ or N $(000\overline{1})$ polarities have been obtained. We show that low growth temperatures (<550°C) and Ga-rich conditions lead to Ga-polar layers, whereas higher growth temperatures (>600°C) and N-rich conditions lead to N-polar layers. Furthermore, the formation of a zinc gallate (ZnGa2O4) interfacial layer between GaN and ZnO has been evidenced, which is responsible for the growth of Ga-polar GaN layers. The structural and optical properties of Ga- and N-polar GaN layers have been characterized and Ga-polar GaN layers exhibit higher crystal quality.