Effect of temperature on lateral growth of ZnO grains grown by MOCVD

ZnO growth on sapphire by MOCVD using dimethylzinc and CO2 as zinc and oxygen precursors was performed. A dense ZnO film with major (0 0 0 2) orientation can be prepared at 350 °C and above with high dimethylzinc flow rate. Result shows that the growth temperature suppresses the lateral growth of ZnO grains, promotes the coalescence of grains but reduces the crystal alignment. To further enhance the crystal alignment, a two-step temperature variation growth method is proposed. Using the two-step growth method, employing the initial growth at lower temperature followed by the growth at higher temperature, a densely packed ZnO film with larger grains and well-aligned (0 0 0 2) crystallographic orientation can be obtained. The effect of temperature on nucleation and growth rate, and its relation to the crystal alignment enhancement is also discussed.