p-Type ohmic contact to MoS2via binary compound electrodes

Abstract

Electronic contacts to two-dimensional (2D) semiconductors, e.g., MoS₂, of both n- and p-type, are important for complementary metal-oxide–semiconductor logic circuitry. Here, via systematic first-principles density-functional theory calculations, we report that both n- and p-type ohmic contact to MoS₂ can be obtained via different surfaces of the same material, the binary compound covellite (CuS). The weak metallicity is helpful to suppress the metal-induced gap states and hence suppress the Fermi-level pinning effect. Importantly, the work functions of different CuS surfaces varies a lot from 3.8 eV to 5.8 eV. The higher work function F(Cu–S) surface forms a p-type contact to MoS₂, and the p-type Schottky barrier height (SBH) can be reduced by increasing the layer number of the MoS₂. The origin of the p-type SBH reduction can be attributed to quasi-bonding both at the F(Cu–S)/MoS₂ interface and between MoS₂ layers, which synergistically shifts the valence band edge up. Due to the large work function variation of CuS surfaces and interface quasi-bonding, p-type ohmic contact to monolayer MoS₂ can be obtained with the P(S) surface. Additionally, the P(Cu)/monolayer MoS₂ junction forms an n-type ohmic contact because of the large work function variation. The widely tunable SBH and contact types of the binary compound CuS/MoS₂ junctions make them promising for high-efficiency electronic and optoelectronic devices.