The synergistic effect between effective mass and built-in electric field for the transfer of carriers in nonlinear optical materials

Abstract

Recent experiments have demonstrated that the typical nonlinear optical material K₃B₆O₁₀Br can be an excellent photocatalyst under ultraviolet (UV) light irradiation. To understand the origin of the photocatalytic activity and further improve its photocatalytic efficiency to develop alternative photocatalysts, the built-in electric field and the electron effective mass and their synergistic effect on transfer and the separation of carriers in K₃B₆O₁₀X (X = Br, Cl) were investigated by means of first-principles calculations. Our results show that the built-in electric field and the smallest effective mass of holes in K₃B₆O₁₀Br are both along the [001] direction. In contrast, the effective masses of electrons are isotropic because of the spherically symmetric s orbitals at the conduction band minimum (CBM). Therefore, the electric field can promote efficient transfer and separation of the photogenerated carriers along the [001] direction. As a consequence, the synergistic effect of built-in electric field and the isotropy of the electron effective mass results in the {001} surface, to which most of the carriers will accumulate, showing the highest photocatalytic activity. Similar results can also be obtained for a K₃B₆O₁₀Cl crystal considering the analogous structure with that of K₃B₆O₁₀Br. The present study may provide theoretical insight to develop the photocatalytic performance of nonlinear optical materials.