Understanding the growth mechanism of graphene on Ge/Si(001) surfaces.

J Dabrowski,M Kot,G Lupina,D Vignaud,T Schroeder,J Maultzsch,Yu S Dedkov,T Schaffus,I Colambo,C Tegenkamp,J Baringhaus,F Herziger,J Avila,G Lippert,M.-C Asensio

doi:10.1038/srep31639

Abstract

The practical difficulties to use graphene in microelectronics and optoelectronics is that the available methods to grow graphene are not easily integrated in the mainstream technologies. A growth method that could overcome at least some of these problems is chemical vapour deposition (CVD) of graphene directly on semiconducting (Si or Ge) substrates. Here we report on the comparison of the CVD and molecular beam epitaxy (MBE) growth of graphene on the technologically relevant Ge(001)/Si(001) substrate from ethene (C2H4) precursor and describe the physical properties of the films as well as we discuss the surface reaction and diffusion processes that may be responsible for the observed behavior. Using nano angle resolved photoemission (nanoARPES) complemented by transport studies and Raman spectroscopy as well as density functional theory (DFT) calculations, we report the direct observation of massless Dirac particles in monolayer graphene, providing a comprehensive mapping of their low-hole doped Dirac electron bands. The micrometric graphene flakes are oriented along two predominant directions rotated by 30° with respect to each other. The growth mode is attributed to the mechanism when small graphene “molecules” nucleate on the Ge(001) surface and it is found that hydrogen plays a significant role in this process.

Highlights

Graphene is widely supposed to be a material on the way to enable new development of many modern technologies[1,2]
The graphene flakes in the chemical vapour deposition (CVD) and molecular beam epitaxy (MBE) prepared films appear similar in scanning electron microscopy (SEM), at least in the growth stage depicted in the figure, but one interesting difference between them is that the MBE prepared flakes have long straight edges, while the CVD synthesized flakes are of much more rounded shape
In the SEM images these areas appear as bright spots, and the ARPES spatial maps show that the density of states at the K-point around the Fermi level EF in the CVD sample vanishes there

Summary

Introduction

Graphene is widely supposed to be a material on the way to enable new development of many modern technologies[1,2] This includes microelectronics and optoelectronics, which require graphene of the highest quality, inexpensively produced and processed on large areas[3,4,5]. Graphene growth on the technologically relevant Ge(001) and Ge(001)/Si(001) wafers has been reported for a CH4-based CVD20 and for a molecular beam epitaxy (MBE) (atomic carbon)[23], respectively. In both cases, the structural and electrical quality of graphene significantly improves at temperatures so high (900–930 °C) that the Ge substrate begins to melt. These mechanisms are compared to those expected for the growth of graphene on Ge(001) from atomic carbon

Methods

Results

Discussion

Conclusion