Control of phase formation of (Al x Ga 1 − x ) 2 O 3 thin films on c-plane Al 2 O 3

• Published in: Journal of physics. D, Applied physics Applied physics, 2020-11, Vol.53 (48), p.485105
• Main Authors: Hassa, Anna, Wouters, Charlotte, Kneiß, Max, Splith, Daniel, Sturm, Chris, von Wenckstern, Holger, Albrecht, Martin, Lorenz, Michael, Grundmann, Marius
• Format: Article
• Language: English
• ISSN: 0022-3727; 1361-6463
• DOI: 10.1088/1361-6463/abaf7d

In this paper, the growth of orthorhombic and monoclinic (Al x Ga 1 −  x ) 2 O 3 thin films on (00.1) Al 2 O 3 by tin-assisted pulsed laser deposition is investigated as a function of oxygen pressure p (O 2 ) and substrate temperature T g . For certain growth conditions, defined by T g  ≥ 580 ° C and p (O 2 ) ≤ 0.016 mbar, the orthorhombic κ -polymorph is stabilized. For T g   =  540 ° C and p (O 2 ) ≤ 0.016 mbar, the κ -, and the β -, as well as the spinel γ -polymorph coexist, as illustrated by XRD 2 θ - ω -scans. Further employed growth parameters result in thin films with a monoclinic β -gallia structure. For all polymorphs, p (O 2 ) and T g affect the formation and desorption of volatile suboxides, and thereby the growth rate and the cation composition. For example, low oxygen pressures lead to low growth rates and enhanced Al incorporation. This facilitates the structural engineering of polymorphic, ternary (Al,Ga) 2 O 3 via selection of the relevant process parameters. Transmission electron microscopy (TEM) studies of a κ  - (Al 0.13 Ga 0.87 ) 2 O 3 thin film reveal a more complex picture compared to that derived from x-ray diffraction measurements. Furthermore, this study presents the possibility of controlling the phase formation, as well as the Al-content, of thin films based on the choice of their growth conditions.