Effects of Cu, Ag, Zn, and Au Doping on the Electronic Structure and Optical Properties of α-Ga2O3: A Density Functional Theory Study

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α-Ga2O3 has attracted significant attention for high-power electronics and deep ultraviolet optoelectronics. Herein, density functional theory calculations were employed to systematically investigate the effects of metal doping, including Cu, Ag, Zn, and Au, on the structural stability, electronic structure, and optical properties of α-Ga2O3. The formation energy analysis reveals that all metal dopants preferentially substitute at the octahedral Ga sites, with lower formation energies under O-rich conditions compared to Ga-rich conditions, among which Zn doping exhibits the lowest formation energy under O-rich conditions, followed closely by Cu, indicating that both Zn and Cu can be readily incorporated into the α-Ga2O3 lattice. Metal doping introduces impurity levels within the band gap through the strong hybridization between dopant d orbitals and O 2p orbitals near the Fermi level, significantly narrowing the effective band gap and transforming the material from a pristine n-type to a p-type semiconductor. The charge density difference analysis further confirms the electron transfer from dopant metal atoms to neighboring O atoms, generating holes as the dominant charge carriers. Among the four dopants, Zn introduces the shallowest acceptor level near the valence band maximum, making it the most promising candidate for achieving effective p-type conductivity, while Cu, Ag, and Au create relatively deeper acceptor states. Furthermore, the optical properties demonstrate that metal doping causes a pronounced red shift in the absorption edge from the ultraviolet to the visible light region, as the impurity levels provide additional electronic transition pathways at lower photon energies. The enhanced visible light absorption, combined with the increased static dielectric constant and modified reflectivity spectra, indicates improved light-harvesting capability of the doped systems. These findings provide important theoretical guidance for the design of α-Ga2O3-based optoelectronic devices.