Bandgap engineering and highly isotropic mobility in Ge-doped ferroelectric-zinc blende phase Ga ₂ O ₃ monolayer

The structural, electronic, and transport characteristics of Ge-doped ferroelectric-zinc blende phase (FZB)-Ga2O3 monolayer are systematically investigated by first-principles calculations, complemented by deformation potential theory and Boltzmann transport theory. Ge dopant preferentially occupies the six-coordinated GaII site with excellent thermodynamic stability under O-rich condition. The higher electronegativity and the smaller ionic radius of Ge4+ relative to Ga3+ promote the stronger Ge-O ionic bonding than that of Ga-O bonds, accompanying with the substantial electron depletion of Ge dopant to the system (losing ~2.30e quantitatively). A pronounced downward displacement of conduction band minimum suggests the n-type conductivity. Applying biaxial strains from 6% to 6%, the bandgap undergoes a steep drop from 3.98 eV to 2.62 eV, which is primarily attributable to the band shifts due to the variations of Ge-O bond lengths. The electron mobility retains strong isotropy under ±6% strain modulations, where the highest μex and μey are of respectively 965.55cm2V1s1 and 1093.09 cm2V1s1 under +4% strain. Moreover, the mobility anisotropy values range from 1.04 to 1.16, illustrating a robust degree of isotropy. Electrical conductivities show the similar trends with the variations of electron mobility. Our present work demonstrates the pronounced tunability of bandgap and highly isotropic electron mobility in Ge-doped 2D FZB-Ga2O3 monolayer, which underscores its strong potential for applications in nanoscale electronic devices.