Engineering multifunctionality in gallium oxide: unveiling novel structural, electronic, and opto-mechanical attributes of gadolinium-doped β-Ga ₂ O ₃ through advanced first-principles design

The design of next-generation wide band gap semiconductors requires both intrinsic optimization and judicious doping strategies. In this work, we comprehensively examine pristine and gadolinium-doped β-Ga₂O₃ (Gd-Ga₂O₃) through a multi-scale computational approach combining HSE06 hybrid DFT, GGA + <i>U</i> and PBESol functionals, MLFF-accelerated <i>ab initio</i> molecular dynamics, and CALYPSO global structure prediction. Gd preferentially substitutes tetrahedral Ga sites in monoclinic β-Ga₂O₃, inducing local lattice distortions but preserving high thermal stability up to 700 K. Mechanical analysis reveals lattice softening without loss of ductility, while electronic calculations show Gd-induced impurity states that enable visible-light absorption and modest band-gap narrowing. Beyond the monoclinic phase, CALYPSO predicts a novel thermodynamically stable triclinic Gd-Ga₂O₃ structure where Gd adopts a distinctive icosahedral coordination. This phase exhibits a remarkably wide direct band gap of 7.0 eV alongside a ∼60% enhancement in visible-light absorption compared to the monoclinic counterpart. Furthermore, it combines high ductility with a greatly increased bulk modulus, reflecting enhanced incompressibility and mechanical robustness. Overall, these results demonstrate that Gd doping substantially tailors the structural, electronic, optical, and mechanical properties of Ga₂O₃. The discovery of a stable triclinic phase with a unique balance of deep-UV transparency, visible-light activity, and superior mechanical strength positions Gd-Ga₂O₃ as a promising multifunctional material for advanced optoelectronic and high-performance device applications.