Rectification at Graphene-Semiconductor Interfaces: Zero-Gap Semiconductor-Based Diodes

A F Hebard,X Miao,B R Appleton,M Lemaitre,S Tongay,B Gila

doi:10.1103/physrevx.2.011002

Abstract

Using current-voltage (I-V) and capacitance-voltage (C-V) measurements, we report on the unusual physics and promising technical applications associated with the formation of Schottky barriers at the interface of a one-atom-thick zero-gap semiconductor (graphene) and conventional semiconductors. When chemical vapor deposited graphene is transferred onto n-type Si, GaAs, 4H-SiC and GaN semiconductor substrates, there is a strong van der Waals attraction that is accompanied by charge transfer across the interface and the formation of a rectifying (Schottky) barrier. Thermionic emission theory in conjunction with the Schottky-Mott model within the context of bond-polarization theory provides a surprisingly good description of the electrical properties. Applications, such as to sensors where in forward bias there is exponential sensitivity to changes in the Schottky barrier height due to the presence of absorbates on the graphene or to analogue devices for which Schottky barriers are integral components are promising because of graphene's mechanical stability, its resistance to diffusion, its robustness at high temperatures and its demonstrated capability to embrace multiple functionalities.

Highlights

Single-atom layers of carbon have been studied intensively after becoming experimentally accessible with techniques such as mechanical exfoliation [1], thermal decomposition on SiC substrates [2], and chemical-vapor deposition (CVD) [3,4]
The good agreement with Schottky-Mott physics within the context of bond-polarization theory is somewhat surprising since the Schottky-Mott picture has been developed for metal/ semiconductor interfaces, not for the single-atomic-layer zero-gap-semiconductor/semiconductor interfaces discussed in this paper
Due to a low density of states, graphene’s Fermi level shifts during the charge transfer across the graphene/semiconductor interface. This shift does not occur at metal/semiconductor or graphite/semiconductor interfaces, where EF remains fixed during Schottky-barrier formation and the concomitant creation of a built-in potential, Vbi with associated band bending. (See Fig. 7.) Another major difference becomes apparent when the diode is under strong reverse bias

Summary

Introduction

Single-atom layers of carbon (graphene) have been studied intensively after becoming experimentally accessible with techniques such as mechanical exfoliation [1], thermal decomposition on SiC substrates [2], and chemical-vapor deposition (CVD) [3,4]. Integration of graphene into semiconductor devices is appealing, there is still very little known about the interface physics at graphene/ semiconductor junctions. To this end, graphene/Si junctions showing successful solar-cell operation have been produced by transferring either CVD-prepared [6] or exfoliated [8] graphene sheets onto Si substrates. The resulting diodes have shown ideality factors (a measure of deviation from thermionic emission) varying from approximately 1:5 [6], which is close to the ideal value of unity, to values in the range of approximately 5–30 on exfoliated graphene [8], implying that additional

Methods

Results

Conclusion