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

TL;DR

This study explores how growth conditions influence the microstructure of heteroepitaxial ZnO thin films on sapphire substrates, revealing different growth modes, domain structures, and defect types depending on temperature and oxygen pressure.

Contribution

It provides detailed insights into the initial growth behavior and microstructural evolution of ZnO films under various deposition parameters, highlighting mechanisms behind domain formation and defect structures.

Findings

Growth mode depends on temperature and oxygen pressure.

Two domain orientations observed at 700°C with defects.

Layered growth with a single epitaxial relationship at 800°C.

Abstract

We have investigated the initial growth behavior and resulting microstructural properties of heteroepitaxial ZnO thin films prepared by pulsed laser deposition on sapphire (0001) substrates. High-resolution x-ray diffraction and transmission electron microscopy studies revealed that the initial growth behavior and the microstructure of the films significantly depend on the growth parameters. ZnO films grown at 700 oC with 20 mTorr O2 partial pressure initiated with a columnar growth mode and contained two kinds of domains. These domains were in-plane orientated either ZnO[112-0]//Al2O3[101-0] or ZnO[101-0]//Al2O3[101-0], and were surrounded by highly defective domain boundaries with threading dislocations. The films grown at 800 oC with 1 mTorr O2 showed 2-dimensional layered growth with only one in-plane epitaxial relationship, ZnO[112-0]//Al2O3[101-0]. Most of the defects in the layered grown films were basal plane stacking faults near the interface between ZnO and the substrate. The formation mechanism of the 30o-twisted domains with the in-plane orientation of ZnO[101-0]//Al2O3[101-0] is discussed.