Characteristics of Ga<sub>2</sub>O<sub>3</sub> epitaxial films on seed layer grown by magnetron sputtering
Authors: Hong Zi-Fan , Chen Hai-Feng , Jia Yi-Fan , Qi Qi , Liu Ying-Ying , Guo Li-Xin , Liu Xiang-Tai , Lu Qin , Li Li-Jun , Wang Shao-Qing , Guan Yun-He , Hu Qi-Ren ,   Key Laboratory of Advanced Semiconductor Devices and Materials, School of Electronic Engineering, Xi'an University of Posts & Telecommunications, Xi'an 710121, China
Published: December 2020

Gallium oxide (Ga<sub>2</sub>O<sub>3</sub>) thin films have great potential applications in UV detectors and power devices; the preparation of high-quality films still needs further studying. In this paper, the Ga<sub>2</sub>O<sub>3</sub> epitaxial thin films are grown by physical sputtering on the seed layer under different power conditions, and the growth mechanism of Ga<sub>2</sub>O<sub>3</sub> epitaxial films are investigated. The introduction of a seed layer provides an artificial nucleation point, which effectively alleviates the lattice mismatch between sapphire substrate and Ga<sub>2</sub>O<sub>3</sub> epitaxial films. thereby improving the quality of the epitaxial layer significantly. Through experiments, it is found that as the power of the epitaxial layer film increases during the growth, the crystal grains agglomerate to a certain size and crack. This physical phenomenon is attributed to the fact that the energy carried by sputtered particles is too large under the condition of high power, which leads the number of particle collisions to increase when they diffuse on the growing crystal surface. The X-ray diffraction, atomic force microscope, field emission scanning electron microscope, ultraviolet spectrophotometer, and photo-luminescence spectrum are used to characterize the structure, morphology, and optical properties of the deposited Ga<sub>2</sub>O<sub>3</sub> thin film. The results show that the epitaxial films are β-Ga<sub>2</sub>O<sub>3</sub> with <inline-formula><tex-math id="M2">\begin{document}$ \left( {\bar 2\;0\;1} \right)$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="22-20200810_M2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="22-20200810_M2.png"/></alternatives></inline-formula> orientation, and the thickness values of thin films are between 202.4 and 292.3 nm. Comparing with the Ga<sub>2</sub>O<sub>3</sub> thin films grown directly on sapphire, the surface particle size increases significantly and the crystal quality is improved greatly under the condition of seed layer. The surface roughness is still maintained at a lower value reaching the device preparation standard. All Ga<sub>2</sub>O<sub>3</sub> epitaxial films show that they have the high transmittance of about 90% in the visible light region (450－800 nm) and drop sharply at 350－400 nm. As the power increases, the absorption edge is blue-shifted and then red-shifted. The estimated band gap is about 4.81－4.96 eV. The PL spectra show that thin films produce blue emission only at 460 nm. It is found that the Ga<sub>2</sub>O<sub>3</sub> films grown on seed layer at a sputtering power of 160 W have the excellent crystal quality. The results should be helpful in implementing the controllable preparation of high-quality β-Ga<sub>2</sub>O<sub>3</sub> thin films in the future.