Effects of substrate temperature and sodium source temperature on Na doping of ZnO by MOCVD

In this paper, Na-doped ZnO thin films were grown by MOCVD using cyclopentadienylsodium (CpNa) as the sodium source. The effects of substrate temperature and sodium source temperature on the properties of Na-doped ZnO thin films were studied. SIMS measurement verified that higher substrate temperature would result in higher Na doping content in ZnO:Na thin films. SEM and Hall measurements revealed that both surface morphology and electrical properties of ZnO:Na thin films showed nonlinear variation with substrate temperature and sodium source temperature. When the substrate temperature or the sodium source temperature was increased, the surface morphology of ZnO:Na thin films turned to sheet structures tilted in all directions first and then back to perpendicular hexagonal structure dominant morphology, and the hole concentration increased first and then decreased. This nonlinear variation trend was ascribed to be related to the variation of doping content and impurity position in ZnO:Na thin films, especially the Na impurity position.