Initial growth behavior and resulting microstructural properties of heteroepitaxial ZnO thin films on sapphire (0001) substrates

Abstract

The initial growth behavior and resulting microstructural properties of heteroepitaxial ZnO thin films prepared by pulsed laser deposition on sapphire (0001) substrates were investigated. High-resolution x-ray diffraction and transmission electron microscopy studies revealed that the initial growth behavior and the microstructure of the films were significantly dependent on the growth parameters employed. ZnO films grown at 700 degrees C with an O-2 partial pressure of 20 mTorr initiated in a columnar growth mode and contained two types of domains. These domains were in plane orientated either ZnO[11 (2) over bar0]parallel to Al2O3[10 (1) over bar0] or ZnO[10 (1) over bar0]parallel to Al2O3[10 (1) over bar0] and were surrounded by highly defective domain boundaries with threading dislocations. ZnO films grown at 800 degrees C with 1 mTorr O-2 showed a two-dimensional layered growth with only one in-plane epitaxial relationship, ZnO[11 (2) over bar0]parallel to Al2O3[10 (1) over bar0]. Most of the defects in the layered grown films were basal plane stacking faults near the interface between the ZnO and the substrate. The mechanism of formation of the 30 degrees-twisted domains with the in-plane orientation of ZnO[10 (1) over bar0]parallel to Al2O3[10 (1) over bar0] is discussed.