Electronic structure modeling of transition metal hyperdoping in β-Ga₂O₃: concentration-dependent band hybridization...

β-Ga₂O₃ holds great promise in deep-ultraviolet optoelectronics, photocatalysis, solar cells, and power electronics due to its superior properties. In this work, the electronic and optical evolution in transition metal impurities (TMI, Cu, Ag, Au)-hyperdoped β-Ga₂O₃ (1.25-6.25 at%) have been investigated using first-principles calculations. The results show that oxygen-rich conditions favor dopant incorporation, with Cu exhibiting the lowest formation energy across all concentrations, indicating superior thermodynamic stability. Crucially, high-concentration doping introduces impurity levels above the valence band maximum that shift progressively toward the valence band edge with increasing concentration, significantly reducing ionization energies. This behavior arises from d-p orbital hybridization and leads to the formation of discrete intermediate bands rather than metallization. Spin-polarized calculations show that Cu doping induces ferromagnetism, Ag doping is non-magnetic, and Au doping exhibits weak antiferromagnetism. Consequently, the optical absorption edge undergoes a pronounced redshift, extending light harvesting from the ultraviolet to the visible-near-infrared range. The optical absorption edge redshifts from ultraviolet to visible-near-infrared, showing distinct dopant-dependent anisotropic responses. These findings establish quantitative concentration-performance relationships for optimizing hyperdoping strategies.

Calculations used the Vienna Ab initio Simulation Package (VASP) with modified Becke-Johnson (MBJ) functional and plane-wave basis set (420 eV cutoff). A 2 × 2 × 2 supercell (160 atoms) employed a 6 × 4 × 12 k-mesh. Formation energies evaluated under O-rich/Ga-rich limits for substitutional doping at Ga1 (tetrahedral) and Ga2 (octahedral) sites. Electronic structure analysis included band structure, projected density of states, and charge analysis. Optical properties computed via dielectric function formalism within independent-particle approximation. Phonon calculations confirmed dynamical stability across all concentrations.