Elimination of interlayer Schottky barrier in borophene/C4N4 vdW heterojunctions via Li-ion adsorption for tunneling photodiodes

Abstract

The nonzero interlayer Schottky barrier leads to a compromise between photodetectivity and photoresponsivity in photodiodes based on vdW heterojunctions. Seeking for the appropriate vdW heterojunction with Ohmic contact and a high tunneling barrier is of great significance to realize high-performance photodiodes. We built borophene/C₄N₄ (B/C₄N₄) vdW heterojunctions with a reduced interlayer Schottky barrier, by combining density functional theory and non-equilibrium Green's function. The adsorption of Li-ions can further tune its Schottky contact into n-type Ohmic contact. The electronic properties of the Li-ion-adsorbed B/C₄N₄ vdW heterojunction, including the separation of hole–electron pairs, the work function, as well as the effective mass of carrier, can be modulated by changing the adsorption site of Li-ions. B/C₄N₄/Li shows the most excellent absorbing capability of the infrared illumination and the strongest negative rectification, due to the highest interlayer tunneling barrier. The bottom surface of the C₄N₄ sublayer is the optimal adsorption site of Li-ions, for the potential application of B/C₄N₄ vdW heterojunctions in tunneling photodiodes. Our work unveils the great significance of Li-ion adsorption in modulating the interlayer Schottky and tunneling barriers in vdW heterojunctions, thus improving their device performance.