Formation of various phases of gallium oxide films depending on substrate planes and deposition gases. (January 2016)

• Record Type: Journal Article
• Authors: Akazawa, Housei
• Is Part Of: Vacuum. Volume 123(2016)
• Page Start: 8
• Page End: 16
• Publication Date: 2016-01
• Subjects: Ga2O3 -- Sapphire substrate -- Crystal phase -- Sputtering -- Crystallization; Vacuum -- Periodicals; 621.55
• DOI: 10.1016/j.vacuum.2015.10.009
• Languages: English
• ISSNs: 0042-207X

Abstract

Abstract: The crystal phases and orientations of Ga2 O3 thin films were investigated by RF magnetron sputtering on sapphire C-planes, sapphire A-planes, and Si(100) substrates either in an O2 or H2 O vapor ambient. When deposited under O2 gas flow, ( 2 ¯ 01)-oriented β-Ga2 O3 grew on sapphire C-planes at 300 °C for both as-crystallization and solid-phase crystallization. In contrast, (110)-oriented α-Ga2 O3 grew on sapphire A-planes above 600 °C. Randomly-oriented polycrystalline β-Ga2 O3 was formed on Si(100) substrates. These experimental results indicate that while a high temperature is needed to form β-Ga2 O3, the activation barrier of nucleation is greatly reduced by hexagonally packed oxygen atoms on sapphire C-planes. Nucleation and/or crystallization on sapphire A-planes require higher temperatures probably because of sparse surface atoms. Nevertheless, pseudomorphic growth of α-Ga2 O3 having the same corundum structure is selected due to the template effect of the substrate at elevated temperatures. Deposition with H2 O severely decelerated crystallization and promoted nucleation of γ-Ga2 O3 . Preferentially (311)-oriented γ-Ga2 O3 was obtained on sapphire C-planes. While pseudomorphic growth of α-Ga2 O3 occurred on sapphire A-planes above 800 °C, small γ-Ga2 O3 crystallites coexisted with them. Conversion between the phases was not observed even at 800 °C, reflecting a high activation barrier for rearrangement of atoms that constitute crystalline lattices. Highlights: Crystal phases of Ga2 O3 films on sapphire and Si(100) have been investigated. ( 2 ¯ 01)-oriented β-Ga2 O3 is formed on Al2 O3 (0001) above 300 °C. (110)-oriented α-Ga2 O3 is formed on Al2 O3 (11 2 ¯ 0) above 600 °C. High temperature is needed to obtain high crystallinity of α-Ga2 O3 . Solid-phase crystallization in the presence of H2 O favors formation of γ-Ga2 O3 .