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P‑Type Spin-Coated Sol-Gel Cr2O3 Layer by Postannealing in Vacuum
Wei-Chih Lai1,2,3, Chan-Hung Hsu4, Bo-Ting Wu1
1Department of Photonics, National Cheng Kung University, Tainan 70101, Taiwan.
ACS Omega
|August 25, 2025
Summary
Postannealing spin-coated sol-gel chromium(III) oxide (Cr2O3) in a vacuum above 500°C successfully activates hole carriers. Vacuum annealing is crucial for achieving high sheet hole concentrations, unlike nitrogen annealing.
Area of Science:
- Materials Science
- Solid State Physics
- Semiconductor Physics
Background:
- Chromium(III) oxide (Cr2O3) is a promising material for electronic applications.
- Activating hole carriers in Cr2O3 is essential for its semiconductor properties.
- Doping-free methods for carrier activation are highly desirable.
Purpose of the Study:
- To investigate the activation of hole carriers in spin-coated sol-gel Cr2O3.
- To determine the optimal postannealing conditions for carrier activation.
- To understand the correlation between annealing environment and electrical properties.
Main Methods:
- Spin-coating of sol-gel Cr2O3 films.
- Postannealing in vacuum and nitrogen (N2) ambient at various temperatures and pressures.
- Sheet hole concentration measurements.
- X-ray Photoelectron Spectroscopy (XPS) for chemical state analysis.
Main Results:
- Successful activation of hole carriers in Cr2O3 by vacuum postannealing above 500°C.
- Sheet hole concentration reached 5 × 10^14 cm^-2 at 680°C in vacuum.
- Nitrogen annealing at 560°C or higher under low pressure (3 mTorr) was ineffective for hole carrier activation.
- Re-annealing N2-treated Cr2O3 in vacuum restored its electrical properties.
- XPS analysis revealed a strong correlation between Cr valence states (Cr2+, Cr4+, Cr5+, Cr6+), oxygen vacancies, and hole carrier creation.
Conclusions:
- Vacuum postannealing is a viable method for activating hole carriers in undoped Cr2O3.
- The annealing atmosphere significantly impacts the electrical properties of Cr2O3.
- Oxygen vacancies and specific chromium oxidation states are key factors in hole carrier generation in Cr2O3.
