Temperature-induced morphological changes of ZnO grown by metalorganic chemical vapor deposition

Changes of morphology during the growth of ZnO on Al2O3 (0 0 0 1) substrates by metalorganic chemical vapor deposition (MOCVD) were investigated as a function of growth temperature (Tg). The morphology of ZnO changes dramatically with Tg. At very low growth temperatures of Tg⩽200 °C, no meaningful ZnO forms. At 200 °C380 °C, ZnO nanowires start to grow on top of a continuous ZnO layer. Both the nanoneedles and the nanowires are not only well aligned both in the out-of- and in the in-plane direction, but also show a very low density of crystalline defects. Our results suggest that Tg is one of the key processing parameters and need to be optimized in a narrow regime in order to grow a desired type of ZnO in MOCVD process.