Microstructural and optical properties of high-quality ZnO epitaxially grown on a LiGaO2 substrate

Abstract

High-quality ZnO films have been reproducibly grown on a LiGaO₂ substrate by chemical vapor deposition with optimized growth parameters. The in-plane epitaxial relationship of ZnO[100]//LiGaO₂[100] is revealed by transmission electron microscopy (TEM). The surface morphology of as-grown ZnO films characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM) demonstrates a very smooth surface with a root-mean-square roughness of 0.6 nm. The full width at half maximum value (FWHM) of 0.03° for the (0002) X-ray rocking curve shows the excellent crystalline quality of as-grown ZnO films. High transparency of the ZnO films in the visible range was revealed by optical transmittance measurements. The strong near-band-edge UV emission accompanied by a negligible defect-related green band emission suggests that the as-grown ZnO films have a high optical quality. Microstructural properties and strain state of the samples were also studied by TEM, X-ray diffraction (XRD) reciprocal space maps and Raman scattering analysis. Substrate compliant deformation, confirmed by the high-resolution TEM analysis, is suggested to be beneficial to decrease the compressive strain in the epilayer and increase the quality of the ZnO. This facile growth process towards high-quality ZnO opens up a broad potential application of high-efficiency ZnO-based devices on a LiGaO₂ substrate.