Influence of Polymorphism on the Electronic Structure of Ga₂O₃

Abstract

The search for new wide-band-gap materials is intensifying to satisfy the need for more advanced and energy-efficient power electronic devices. Ga2O3 has emerged as an alternative to SiC and GaN, sparking a renewed interest in its fundamental properties beyond the main β-phase. Here, three polymorphs of Ga2O3, α, β, and ε, are investigated using X-ray diffraction, X-ray photoelectron and absorption spectroscopy, and ab initio theoretical approaches to gain insights into their structure–electronic structure relationships. Valence and conduction electronic structure as well as semicore and core states are probed, providing a complete picture of the influence of local coordination environments on the electronic structure. State-of-the-art electronic structure theory, including all-electron density functional theory and many-body perturbation theory, provides detailed understanding of the spectroscopic results. The calculated spectra provide very accurate descriptions of all experimental spectra and additionally illuminate the origin of observed spectral features. This work provides a strong basis for the exploration of the Ga2O3 polymorphs as materials at the heart of future electronic device generations.

Study of Ti contacts to corundum α-Ga2O3

“…The film consists dominantly of α-Ga 2 O 3 columns, with amorphous and ε-Ga 2 O 3 inclusions located between the columns [15]. The films were unintentionally n-doped, as was observed using X-ray absorption spectroscopy and soft X-ray photoelectron spectroscopy by Swallow et al on comparable α-Ga 2 O 3 films deposited by PEALD [16].…”

Two-dimensional Ferroelectric Ga2O3 Bilayers with Unusual Strain-engineered Interlayer Interactions

“…Although bulk Ga 2 O 3 polymorphs are ionic materials [67][68][69], our calculations so far show that the FE-ZB Ga 2 O 3 bilayer systems exhibit typical vdW interlayer interactions in relaxed and moderate strained states from -6 to 6%. However, with increase of biaxial tensile strain, an unexpected phase transition of the interlayer interaction appears around 7% strain.…”

“…Unlike the other vdW systems, strong ionic nature of the Ga-O bond (Pauling's ionicity of Ga 2 O 3 , ∼0.49 [74]) leads to the fact that the lattice structure of Ga 2 O 3 is governed by two principle factors: (i) the relative charges of the ions and (ii) their relative size (folding factor). Our previous study [39] shows that the average charge transfer from Ga to O atoms is about 1.80e per Ga atom for both 2D and bulk phases, and the big Ga cations are energetically favorable to occupy tetrahedral (4-fold) and octahedral (6-fold) sites surrounding by the O anions [69]. Therefore, the mechanism of the transition can be rationalized by the folding switching of the interlayer facing Ga atoms, as shown in Figure 6.…”

Ab Initio Quantum-Mechanical Predictions of Semiconducting Photocathode Materials

“…In that work, we noticed that the local environment of the individual Cs atoms strongly impacts the X-ray spectral features. This is expected based on the knowledge over even more complex systems, such as Ga O , where crystallographically inequivalent atoms are also chemically inequivalent and exhibit different coordination [ 103 , 130 ]. In Ref.…”