Tuning electronic structure of monolayer InP in contact with graphene or Ni: effect of a buffer layer and intrinsic In and P-vacancy.

Monolayer indium triphosphide (m-InP), predicted theoretically to be a new 2D semiconducting material, exhibits a promising opportunity for applications in electronic and optoelectronic devices [N. H. Miao, et al., J. Am. Chem. Soc., 2017, 139, 11125-11131]. For these applications, excellent contact performance between m-InP and the electrodes is vital. In this work, by first-principles calculations, the electronic structures of m-InP in contact with graphene (G) and Ni are investigated and the contact characters are further tuned by inserting a buffer layer, e.g., a G or BN monolayer (m-BN) along with the introduction of intrinsic P- and In-vacancy defects. For m-InP in contact with G, inserting an m-BN can alter the contact character from an n-type to a p-type Schottky contact. This is consistent with the prediction of the Schottky-Mott rule, indicating that Fermi level pinning is removed in the interface. However, for the contact with Ni, if an m-BN or G is inserted into the interface, an n-type Ohmic contact is obtained, rather than the p-type Schottky one based on the Schottky-Mott rule. We attribute this inconsistency to the effect of electron transfer from m-BN or G to Ni, which leads to a decreased work function for Ni. Additionally, introducing In- and P-vacancy defects can reduce the Schottky barrier in the interfaces between m-InP and G or Ni. Moreover, if m-BN is inserted into these defect-containing interfaces, an n-type Ohmic contact could be achieved and dominate the contact character. Our results offer deeper insights into factors such as the Fermi level pinning on the band alignment of the interfaces between m-InP and G or Ni, and how the contact characters are improved by inserting a buffer layer along with the introduction of In- and P-vacancy defects.