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This study focuses on the impact of high-doping impurities (>1018 cm−3) on the morphology of homoepitaxially grown (100) 4° off β-Ga2O3 film, as well as incorporating insights from the Cabrera–Vermilyea model (C–V model). Using atomic force microscopy imaging, we reveal that under low-supersaturation conditions, dopant-induced impurities lead to irregular step formation and growth stalling, inducing the step-bunching formation consistent with C–V model predictions. Conversely, higher supersaturation conditions restore desired step-flow morphology, resembling low-impurity growth states. It is also shown that the step-bunching formed under lower supersaturation conditions and high-impurity concentration might induce unwanted structural defects and compensate the free carriers. These findings underscore the delicate interplay between dopant concentrations, growth morphology, and supersaturation in metalorganic vapor phase epitaxy-grown (100) β-Ga2O3 films, providing a comprehensive understanding of optimizing their electrical properties with respect to power electronics applications. [ABSTRACT FROM AUTHOR]

In this paper, we employ in situ transmission electron microscopy to study the disorder–order phase transition from amorphous Ga2O3 to γ-Ga2O3 and then to β-Ga2O3. The in situ studies are complemented by ex situ annealing experiments, of which the results are analyzed by x-ray diffraction and high resolution (scanning) transmission electron microscopy. Amorphous Ga2O3 deposited at 100 °C by molecular beam epitaxy crystallizes at 470 °C in the γ phase (F d 3 ̄ m) , which undergoes a phase transition to the β phase above 500 °C. Between 500° and 900 °C, we find a mixture of γ-Ga2O3 and β-Ga2O3 coexisting. Above 950 °C, we find only β-Ga2O3. Through our analyses and by considering symmetry relations, we have constructed a coincidence site lattice of both structures containing a common fcc-type sublattice occupied by oxygen atoms, the cation sites of β-Ga2O3 common to both phases, and partially occupied cation sites in the γ phase corresponding to the interstitial sites in the β phase. We assign the atomic displacements within this lattice responsible for transforming the initially disordered spinel structure with partially occupied cation sites into the well-ordered lattice of β-Ga2O3. We identify this transition as a reconstructive disorder-to-order phase transition, mediated by the exchange of cations to next nearest neighbor sites. Our model not only explains recent observations of the formation of γ-Ga2O3 during implantation for n-type doping and the subsequent recovery of β-Ga2O3 following annealing but also holds potential for inspiring understanding in other materials with similar phase transitions. [ABSTRACT FROM AUTHOR]

In this paper, the growth of orthorhombic and monoclinic (AlxGa1 − 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. For certain growth conditions, defined by ≥ 580°C and p(O2) ≤ 0.016 mbar, the orthorhombic κ-polymorph is stabilized. For = 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 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. [ABSTRACT FROM AUTHOR]

In this paper, the growth of orthorhombic and monoclinic (AlxGa1 − 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. For certain growth conditions, defined by ≥ 580°C and p(O2) ≤ 0.016 mbar, the orthorhombic κ-polymorph is stabilized. For = 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 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. [ABSTRACT FROM AUTHOR]

In this work, we investigate the growth of monoclinic β-(In x Ga 1- x ) 2 O 3 alloys on top of (010) β-Ga 2 O 3 substrates via plasma-assisted molecular beam epitaxy. In particular, using different in situ (reflection high-energy electron diffraction) and ex situ (atomic force microscopy, X-ray diffraction, time-of-flight secondary ion mass spectrometry, and transmission electron microscopy) characterization techniques, we discuss (i) the growth parameters that allow for In incorporation and (ii) the obtainable structural quality of the deposited layers as a function of the alloy composition. In particular, we give experimental evidence of the possibility of coherently growing (010) β-(In x Ga 1- x ) 2 O 3 layers on β-Ga 2 O 3 with good structural quality for x up to ≈ 0.1. Moreover, we show that the monoclinic structure of the underlying (010) β-Ga 2 O 3 substrate can be preserved in the β-(In x Ga 1- x ) 2 O 3 layers for wider concentrations of In ( x ≤ 0.19). Nonetheless, the formation of a large amount of structural defects, like unexpected ( 10 2 ̅ ) oriented twin domains and partial segregation of In is suggested for x > 0.1. Strain relaxes anisotropically, maintaining an elastically strained unit cell along the a * direction vs plastic relaxation along the c * direction. This study provides important guidelines for the low-end side tunability of the energy bandgap of β-Ga 2 O 3 -based alloys and provides an estimate of its potential in increasing the confined carrier concentration of two-dimensional electron gases in β-(In x Ga 1- x ) 2 O 3 /(Al y Ga 1- y ) 2 O 3 heterostructures.