Effective Work-function Increase Observed in Al/SiO2/Si Junction with Graphene Interlayer at Al/SiO2 Interface

Abstract

The work function of a metal electrode is one of the major factors determining the threshold voltage of metal/oxide/semiconductor (MOS) junction. In this work, we report the large effective work-function increase in Al/SiO2/Si junction from ~3.31 to ~4.35 eV when a graphene is inserted at the Al/SiO2 interface, confirmed by capacitance-voltage (C-V) measurements. This increase of effective work-function is expected to originate from the electric dipole layer formed between graphene and Al layers due to the electron orbital overlapping (interaction dipole layer) [1,2]. The device-physical analysis of solving Poisson equation for the flat-band junctions with the parameters extracted from the measurements shows that the interaction dipole layer should have its negative side on the graphene side. The electrostatic effect of interaction dipole layer is also confirmed for a Pt electrode possessing a relatively high work-function. For the Pt electrode, the effective work-function decreases from ~4.85 to ~4.68 eV, indicating that the positive side of interaction dipole layer is toward the graphene layer. Our works imply that Al can be used commonly for both n-MOS and p-MOS with the selectively-patterned graphene interlayer thanks to the large change of its effective work-function (~1.04 eV) comparable to the Si band gap (~1.12 eV).

[1] P. A. Khomyakov, et al., Phys. Rev. B, 79(19), 195425 (2009). [2] H. H. Yoon, et al., ACS Appl. Mater. Interfaces, 11(50), 47182-47189 (2019).