Origin of weak Fermi level pinning at the graphene/silicon interface

Abstract

The mechanisms governing the formation of Schottky barriers at graphene/hydrogenpassivated silicon interfaces where the graphene plays the role of a two-dimensional (2D) metal electrode have been investigated by means of x-ray photoemission spectroscopy and density functional theory (DFT) calculations. To control the graphene work function without altering neither the structure nor the band dispersion of graphene we used a method that consists in depositing small amounts of gold forming clusters on the graphene/hydrogenpassivated silicon system under ultra-high vacuum environment. We observe from experimental measurements that the Fermi level is mainly free from pinning at the graphene/hydrogen-silicon interface whereas for a semi-infinite metal on silicon the Fermi level is almost fully pinned. This alleviation of the Fermi level pinning observed with the graphene layer is explained by DFT calculations showing that the graphene and the semiconductor are decoupled and that the metal-induced gap states (MIGS) density at the silicon midgap at the interface is very low (< 5 × 10 10 states/eV/cm 2 ). The important conclusion that stems from the DFT results analysis is that the low MIGS density at the semiconductor midgap is related to the 2D nature of the graphene layer. More precisely, the MIGS density is low owing to the lack of propagating states perpendicular to the graphene layer. This finding brings precious information to understand the mechanisms that govern the

A weakened Fermi level pinning induced adsorption energy non-charge-transfer mechanism during O2 adsorption in silicene/graphene heterojunctions

“…39 These results in 2D metals/2D semiconductors are consistent with 2D metal/three-dimensional semiconductor interfaces. 40 These results prove the previous conjecture that the presence of graphene can achieve quasi-ohmic contact, 41,42 which weakens the FLP of silicene. 32…”

“…39 These results in 2D metals/2D semiconductors are consistent with 2D metal/three-dimensional semiconductor interfaces. 40 These results prove the previous conjecture that the presence of graphene can achieve quasi-ohmic contact, 41,42 which weakens the FLP of silicene. 32 In the case of little difference in electron transfer, it is particularly important to study how the weakened Fermi level energy pinning affects E ad and uncover the unknown contribution to E ad .…”

High-performance gold/graphene/germanium photodetector based on a graphene-on-germanium wafer

“…There are no dangling bonds on the surface of graphene, so the alleviation of FLP may be not caused by dangling bonds passivation at the surface, but by reduction of the MIGS effect of the inserted graphene layer, consistent with reported work using 2D material insertion [23,36,37]. The incomplete Fermi level depinning may be generated from the Fermi level pinning at graphene/Ge interface [38,39].…”

In-Depth Analysis on Self Alignment Effect of the Fermi-Level Using Graphene on Both n- and p-Type Semiconductors

“…(i) and (ii) indicate the Gr/semiconductor, and metal/Gr interfaces, respectively. (i) The inserted Gr layer was mechanically transferred onto the substrate, forming a VdW contact, which breaks the metal–semiconductor interaction and inhibits the propagation of states perpendicular to Gr . Moreover, 2D semimetal Gr has a limited electronic density of states (DOS) near the Dirac point; therefore, few MIGS are induced at the surface of the semiconductor. , Owing to these features, the MIGS, which mainly causes FL pinning, was reduced, leading to FL unpinning at the interface between the Gr and semiconductor.…”

“…Graphene (Gr) is a 2D semimetallic material composed of a single layer of carbon atoms. Although it is known to have a zero bandgap, in which the conduction and valence bands cross at the Dirac point, it can effectively suppress MIGS owing to the VdW contact. − Furthermore, when Gr is in contact with the metal, a charge-sharing effect occurs from Gr to the metal, which aligns the FLs on both sides of the contact. Considering these features, Gr is a qualified interlayer candidate for a universal MIS contact structure suitable for both n- and p-type semiconductors.…”