【Epitaxy Papers】Sol-gel synthesis and optical band structure modulation of wafer-scale Cr-Doped β-Ga₂O₃ thin films

      Researchers from Nanjing University of Information Science and Technology have published a dissertation titled " Sol-gel synthesis and optical band structure modulation of wafer-scale Cr-Doped β-Ga₂O₃ thin films " in Physica Scripta.

Abstract

      Gallium oxide (Ga₂O₃) has emerged as a promising ultra-wide bandgap semiconductor for next-generation high-power electronics and solar-blind ultraviolet photodetection. However, achieving high-quality, large-area thin films through cost-effective methods and tailoring their electronic properties remain significant challenges. In this work, wafer-scale undoped and chromium (Cr)-doped β-Ga₂O₃ thin films were successfully synthesized on 2 inch sapphire substrates using a low-cost, non-vacuum sol-gel spin-coating method. The influence of annealing temperature and Cr doping on the structural and optical properties was systematically investigated. The elemental and structural analyzes confirmed the formation of the monoclinic β-phase at annealing temperatures of 600 °C and 700 °C, with Cr ions effectively incorporated into the Ga₂O₃ lattice at Ga substitutional sites. Optical characterization revealed that all films exhibit high transparency exceeding 90% in the 300–1100 nm range. Increasing annealing temperature sharpened the absorption edge and induced a red shift, reducing the optical band gap from 5.00 eV (400 °C) to 4.93 eV (700 °C). Cr doping further decreased the band gap to 4.85 eV and enhanced absorption in the visible region. Theoretical calculations elucidated that Cr³⁺ ions and oxygen vacancies introduce localized mid-gap states, providing alternative transition pathways that dominate the sub-bandgap excitations and drive the observed spectral redshift. The dielectric function and absorption spectra from density functional theory align with experimental trends. These findings establish the sol-gel technique as a viable industrial-scale alternative for semiconductor engineering and provide critical insights into bandgap tailoring via transition metal doping and defect management.

DOI：

https://iopscience.iop.org/article/10.1088/1402-4896/ae70d9