Electron-Beam-Induced Crystallization of Amorphous Gallium Oxide Thin Films Using Scanning Transmission Electron Microscopy

Abstract

Crystallization of amorphous materials using an electron beam is a promising technique for crystallizing minute regions. The crystallization behavior of amorphous gallium oxide (Ga₂O₃) thin films under electron-beam irradiation was investigated with a scanning transmission electron microscope, and patterned line drawing was performed using its line-scan mode. The Ga₂O₃ thin films exhibited crystallization at threshold electron-beam doses in the range of 53–144 C/cm². The γ- and β-Ga₂O₃ forms crystallized as grains with an average size of 7 nm. The crystallization volume increased with doses. Crystallized Ga₂O₃ polymorphs varied predominantly from γ- to β-Ga₂O₃ with increased doses. The dose dependence of Ga₂O₃ polymorphs was attributed to the variation in the coordination number of oxygen ions to gallium ions and the formation of oxygen vacancies caused by the electron-beam irradiation. The letter N predominantly composed of β-Ga₂O₃ single crystals could be drawn with an approximately 10 nm line width in an amorphous Ga₂O₃ thin film using the line-scan mode. Crystallized β-Ga₂O₃ at the onset of the line-scan was inferred to grow epitaxially with subsequent scanning, realizing a letter N predominantly composed of single-crystal β-Ga₂O₃.