Control of phase formation of (Al_xGa_1 − x)₂O₃ thin films on c-plane Al₂O₃

Abstract

In this paper, the growth of orthorhombic and monoclinic (Al x Ga1 − x )2O3 thin films on (00.1) Al2O3 by tin-assisted pulsed laser deposition is investigated as a function of oxygen pressure p(O2) and substrate temperature T g . For certain growth conditions, defined by T g ≥ 580°C and p(O2) ≤ 0.016 mbar, the orthorhombic κ-polymorph is stabilized. For T g = 540°C and p(O2) ≤ 0.016 mbar, the κ-, and the β-, as well as the spinel γ-polymorph coexist, as illustrated by XRD 2θ-ω-scans. Further employed growth parameters result in thin films with a monoclinic β-gallia structure. For all polymorphs, p(O2) 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)2O3 via selection of the relevant process parameters. Transmission electron microscopy (TEM) studies of a κ - (Al0.13Ga0.87)2O3 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.

Electrical and Recombination Properties of Polar Orthorhombic κ-Ga2O3 Films Prepared by Halide Vapor Phase Epitaxy

“…Thus, although a growth of single-domain films has been reported [ 34 ], in most cases, κ-Ga 2 O 3 can be considered to be a nanocrystalline material. The boundaries between these rotational domains present an obstacle to the current flow in the growth plane and, for a long time, have prevented the research of the electrical properties of κ-Ga 2 O 3 films; however, more recently, heterostructures and quantum wells of κ-(Al x Ga 1−x ) 2 O 3 /κ-Ga 2 O 3 with different Al mole fractions and hence different band structures have been demonstrated, and vertical NiO/κ-Ga 2 O 3 structures have been successfully fabricated by pulsed laser deposition [ 35 , 36 ]. This major disadvantage impairing the practical use of κ-Ga 2 O 3 -based structures and devices was partly overcome in [ 19 ] by employing ELOG growth on sapphire substrates masked with thin TiO 2 and patterned with either stripes or dots of SiO 2 ; this facilitated the formation of single-domain κ-Ga 2 O 3 films with good crystalline quality using HVPE.…”

Structural and Elastic Properties of α‐(AlxGa1−x)2O3 Thin Films on (11.0) Al2O3 Substrates for the Entire Composition Range

“…[ 6 ] The second‐most stable structure is the orthorhombic κ ‐phase, for which ternary PLD thin films were already reported. [ 7–11 ] The third‐most stable polymorph is the rhombohedral α‐phase.…”

Epitaxial Growth of κ‐(AlxGa1−x)2O3 Layers and Superlattice Heterostructures up to x = 0.48 on Highly Conductive Al‐Doped ZnO Thin‐Film Templates by Pulsed Laser Deposition

“…[ 24,26 ] The ZnO/ZnO:Al template might change the actual growth temperature due to a different equilibrium with the radiation field of the resistive heater or changes the incorporation of Al in general. A difference in growth temperature influences both Al incorporation, which decreases with decreasing due to the lower amount of volatile suboxides that are formed and desorbed, [ 64 ] and the unit cell volume in general that could change the evolution of in‐plane lattice constants. Regarding all these factors, the relation according to Equation (2) is in agreement with the one obtained in a previous study.…”