Microstructural analysis of heteroepitaxial β-Ga <sub>2</sub> O <sub>3</sub> films grown on (0001) sapphire by halide vapor phase epitaxy
Yuewen Li, Xiangqian Xiu, Wanli Xu, Liying Zhang, Zili Xie, Tao Tao, Peng Chen, Bin Liu, Rong Zhang, Youdou Zheng
Abstract
Abstract ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover> <mml:mn>2</mml:mn> <mml:mo>ˉ</mml:mo> </mml:mover> </mml:math> 01)-oriented β-Ga 2 O 3 films have been grown on (0001) sapphire substrates using the halide vapor phase epitaxy method. The as-grown β-Ga 2 O 3 films exhibit highly textured with domain-like surface morphologies and the root-mean-square roughness is measured at 6.2 nm using atomic force microscopy. The microstructure characteristics of the β-Ga 2 O 3 film have been investigated comprehensively to understand the origin for the domain-like morphologies. Two in-plane rational domains with mirror-symmetrical atomic arrangement have been identified along the [010] axis of β-Ga 2 O 3 by high resolution transmission electron microscopy, which are caused by the (0001) sapphire substrate symmetry. Various defects, including twinned crystals, inversion domains and domain boundaries etc, have been observed, leading to the rough surfaces and poor crystalline quality of β-Ga 2 O 3 grown on non-angled (0001) sapphire substrate. Schematic diagrams and the oxygen atomic arrangements of β-Ga 2 O 3 on ∼7° off-angled (0001) sapphire substrate toward the 〈11 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover> <mml:mn>2</mml:mn> <mml:mo>ˉ</mml:mo> </mml:mover> </mml:math> 0〉 plane were proposed to illustrate the in-plane quasi-epitaxial relationships between the β-Ga 2 O 3 (400) film and the sapphire (11 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover> <mml:mn>2</mml:mn> <mml:mo>ˉ</mml:mo> </mml:mover> </mml:math> 3) substrate, and to explain the single domain growth mechanism. The results would be helpful for improving the surface morphologies and crystalline quality of heteroepitaxial Ga 2 O 3 films.