Ohmic contact mechanism and charge redistribution of MoS₂/M_n+ ₁X_nO₂ heterostructures

Abstract Several M n+1 X n O 2 compounds exhibit work functions higher than those of three-dimensional metals, enabling the formation of Ohmic contact heterostructures with MoS 2 , which enhances the catalytic activity of MoS 2 for the hydrogen evolution reaction. However, the Schottky barrier height (SBH) in these Ohmic contact heterostructures does not adhere to the Schottky-Mott limit, leaving the Ohmic contact mechanism between MoS 2 and M n+ 1 X n O 2 unclear and hindering further investigations into these heterostructures. In this study, we investigate 22 MoS 2 /M n+ 1 X n O 2 heterostructures using the unfolding method. Among these, the eight M n+ 1 X n O 2 compounds—Cr 2 CO 2 , Mo 2 CO 2 , V 2 CO 2 , W 2 CO 2 , Cr 2 NO 2 , V 2 NO 2 , Ti 3 C 2 O 2 and V 4 C 3 O 2 —form p-type Ohmic contacts with MoS 2 . In contrast, the twelve compounds—Hf 2 CO 2 , Nb 2 CO 2 , Ta 2 CO 2 , Ti 2 CO 2 , Zr 2 CO 2 , Mo 2 NO 2 , Ti 2 NO 2 , Ti 3 N 2 O 2 , Zr 3 C 2 O 2 , Nb 4 C 3 O 2 , Ta 4 C 3 O 2 and Ti 4 N 3 O 2 —create p-type Schottky contacts, while Hf 2 NO 2 and Zr 2 NO 2 form n-type Schottky contacts with MoS 2 . In the Ohmic contact heterostructures, out-of-plane orbital states hybridize to form a splitting band, allowing the highest valence band of MoS 2 to cross the Fermi level and achieve hole doping. This splitting band not only results in a SBH that does not conform to the Schottky–Mott limit but also redistributes charge density. Notably, the heterostructures formed by Cr 2 CO 2 , Mo 2 CO 2 , V 2 CO 2 , W 2 CO 2 , Cr 2 NO 2 , V 2 NO 2 , V 4 C 3 O 2 , and MoS 2 exhibit charge polarity distribution, whereas MoS 2 /Ti 3 C 2 O 2 does not demonstrate charge polarity distribution.