Defect States in the Electronic Structure of Ga₂O₃ Transparent Conductive Oxide Surfaces

Area of Science:

• Materials Science
• Surface Science
• Solid State Physics

Background:

• Defect states significantly influence electronic device performance, with oxygen vacancies being common in oxides.
• Gallium oxide (Ga₂O₃) is a promising material for electronic devices, but understanding its defect states is crucial for optimizing performance.
• Surface defects can act as recombination centers, degrading device efficiency.

Purpose of the Study:

• To investigate the electronic surface structure of differently processed Ga₂O₃ samples using depth-resolved spectroscopy.
• To identify and characterize defect states in Ga₂O₃ thin films and single crystals.
• To correlate spectral features with defect presence and distribution using theoretical calculations.

Main Methods:

• Soft and hard X-ray photoelectron spectroscopy (PES and HAXPES) with photon energies from 0.1 to 6.3 keV.
• Depth-resolved analysis of Ga₂O₃ thin films and β-Ga₂O₃ single crystals (before and after Ar⁺ ion treatment).
• Density functional theory (DFT) calculations for spectral analysis and band structure interpretation.

Main Results:

• DFT calculations accurately described the spectra of the pristine β-Ga₂O₃ single crystal.
• Ga₂O₃ thin films and Ar⁺-ion treated β-Ga₂O₃ exhibited spectral broadening and additional intensity near the valence band maximum, indicative of defect states.
• The observed defect-induced spectral features varied with probing depth, suggesting surface localization.

Conclusions:

• Surface defects in Ga₂O₃, particularly in thin films and after ion treatment, significantly alter the electronic band structure.
• PES and HAXPES, combined with DFT, are effective tools for characterizing defect states in Ga₂O₃.
• Understanding and controlling surface defects are critical for the development of high-performance Ga₂O₃-based electronic devices.