Gate-controlled carrier injection into hexagonal boron nitride

First-principle calculations show that free-electron carriers are induced in few-layer hexagonal boron nitride ($h$-BN) by applying an external electric field. The electric field substantially shifts the particular states downward, and they finally cross the Fermi level under an electric field of a few volts per nanometer. In the metallic phase of $h$-BN, the carriers are distributed not only at atomic sites but also in the spacious regions in $h$-BN. It is found that the threshold voltage resulting in metal–insulator transition decreases as the number of layers increases. This indicates the possibility of realizing a two-dimensional metallic layered material without the chemical doping of atoms or molecules.

Figure 1

A side view of a thin film of $h$-BN comprising eight atomic layers. The topmost and bottom-most layers face the electrodes. White and gray circles denote B and N atoms, respectively.

Figure 2

Electronic energy band of a thin film of $h$-BN comprising eight atomic layers under (a) a zero electric field and (b) 0.41 V/Å electric field. Energies are measured from (a) the top of the valence band and (b) the Fermi level. (c) Fermi surfaces (lines) for eight-layer graphite under an electric field of 0.41 V/Å.

Figure 3

Contour plot of charge density at the Fermi energy of an eight-layer $h$-BN thin film under an electric field of 0.41 V/Å. Each contour represents twice (or half) the density of the adjacent contour.

Figure 4

Threshold voltage for free-electron carriers in $h$-BN and graphite thin films as a function of the number of layers. Solid and open circles denote the thresholds for $h$-BN and graphite thin films, respectively.