P-type Ca-doped two-dimensional Ga2O3 with strain-modulated high hole mobility and anisotropy

The realization of p-type conductivity with substantial hole mobility remains challenging in emerged wide-bandgap two-dimensional (2D) β-Ga2O3. The substitution of Ca2+ on Ga3+ site is one of the efficient ways to achieve p-type conductivity theoretically. In this work, by employing first-principles calculations with Perdew-Burke-Ernzerhof and Heyd-Scuseria-Ernzerh hybrid functionals, deformation potential and Boltzmann transport theories, the structural stabilities, band structures, hole mobilities and p-type conductivities of Ca-doped 2D β-Ga2O3 are systematic investigated. Firstly, the Ca dopant exhibits an energetically favorable substitution at the GaI site (CaGaI) under O-rich environment, accompanying with superior structural stabilities. Secondly, the electronic structure calculations demonstrate that the Ca impurity can induce a shallow acceptor level and act as an effective p-type dopant. Finally, ±8% strains have been used as a tuning knob in CaGaI, which modulate the bandgaps from 4.73 to 3.76 eV. The hole mobility along y-direction is increased from 246.62 cm2V1s1of unstrained CaGaI to 568.48 cm2V1s1 under 4% tensile strain, accompanying with a twofold enhanced hole mobility anisotropy. Si (111) is predicted as an ideal substrate for Ca-doped 2D β-Ga2O3 film characterized by a high hole mobility along y-direction based on lattice mismatch evaluations. The direct tunable bandgap, the ultra-high hole mobility, the enhanced anisotropy and p-type conductivity highlight its significant potential for nanoscale electronic applications.