Control of ZnO (0001)/Al2O3 (1120) surface morphologies using plasma‐assisted molecular beam epitaxy

The surface morphologies of ZnO thin films grown on Al2O3 (112 0) (a‐plane sapphire) substrate by plasma‐assisted molecular beam epitaxy (PAMBE) were systematically investigated by in situ reflection high energy electron diffraction (RHEED) and ex situ atomic force microscopy (AFM) as a function of Zn beam flux intensity and substrate temperature. The ZnO films are uniquely (0001 ) oriented with no trace of secondary orientation. A phase diagram for ZnO growth was established, which described the ZnO growth mode transition at fixed O2 flow rate of 0.3 sccm. For the growth at 750 °C with Zn beam flux of 3.6 × 10–7 Torr, the RHEED showed a (3 × 3) pattern and a smooth surface represented by atomically flat terraces and half unit cell high steps (∼0.26 nm, a charge neutral unit of ZnO) was observed corresponding to a monolayer or bilayer thickness of Zn–O along the c ‐axis of (0001 ) ZnO. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)