Control of ZnO (000$ \bar 1$)/Al2O3 (11$ \bar 2$0) surface morphologies using plasma‐assisted molecular beam epitaxy

Abstract

AbstractThe surface morphologies of ZnO thin films grown on Al2O3 (11$ \bar 2 $0) (a‐plane sapphire) substrate by plasma‐assisted molecular beam epitaxy (PAMBE) were systematically investigated by in situ reflection high energy electron diffraction (RHEED) and ex situ atomic force microscopy (AFM) as a function of Zn beam flux intensity and substrate temperature. The ZnO films are uniquely (000$ \bar 1 $) oriented with no trace of secondary orientation. A phase diagram for ZnO growth was established, which described the ZnO growth mode transition at fixed O2 flow rate of 0.3 sccm. For the growth at 750 °C with Zn beam flux of 3.6 × 10–7 Torr, the RHEED showed a (3 × 3) pattern and a smooth surface represented by atomically flat terraces and half unit cell high steps (∼0.26 nm, a charge neutral unit of ZnO) was observed corresponding to a monolayer or bilayer thickness of Zn–O along the c ‐axis of (000$ \bar 1 $) ZnO. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)