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

Abstract

The work-function of a metal electrode is an essential factor 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 interlayer is inserted at the Al/SiO2 interface, ensured from the flat-band voltage (VFB) increase in the capacitance-voltage (C-V) measurements. The graphene interlayer is found to be p-type doped in the transfer curve (drain-to-source current vs. gate voltage, IDS-VG) of graphene field-effect transistor (GFET), considered to be due to the oxygen dangling bonds on the SiO2 surface. With the device parameters extracted from the measured C-V and IDS-VG characteristics, we also performed the electrostatic analysis by solving Poisson equation for the flat-band condition. An electric dipole layer is predicted theoretically to form between Al and graphene stemming from the electron orbital overlapping (interaction dipole layer). According to the calculation, the effective work-function increase is considered to indicate that the negative side of interaction dipole layer is toward the graphene layer and thus the electron potential increases across the interface from Al to graphene. The electrostatic effect of interaction dipole layer is also observed with Pt electrode. This time, the effective work-function is measured to decrease from ~4.85 to ~4.68 eV, implying that the positive side of interaction dipole layer is toward the graphene layer. Thanks to the large effective work-function tuning (~1.04 eV) comparable to the Si band gap (~1.12 eV), it might be feasible to construct the dual-metal gate CMOS system just with Al electrodes accompanied by area-specific underlying graphene interlayer.