Abstract
Graphene epitaxy on germanium by chemical vapor deposition is a promising approach to integrate graphene into microelectronics, but the synthesis is still accompanied by several challenges such as the high process temperature, the reproducibility of growth, and the formation of etch pits during the process. We show that the substrate cleaning by preannealing in molecular hydrogen, which is crucial to successful and reproducible graphene growth, requires a high temperature and dose. During both substrate cleaning and graphene growth, etch pits can develop under certain conditions and disrupt the synthesis process. We explain the mechanisms how these etch pits may form by preferential evaporation of substrate, how substrate topography is related to the state of the cleaning process, and how etch pit formation during graphene growth can be controlled by choice of a sufficiently high precursor flow. Our study explains how graphene can be grown reliably on germanium at high temperature and thereby lays the foundation for further optimization of the growth process.
Highlights
The unique properties of graphene, such as its flat form factor, its high carrier mobility, its tunable Fermi level, and its plasmonic activity, make this material a candidate for a variety of applications in microelectronics, such as radiofrequency electronics,[1] optoelectronics,[2,3,4] and chemical sensing.[5]large-scale implementation of graphene in microelectronics is, to date, obstructed by the difficulties of synthesis and integration of the graphene film into mainstream CMOS technology
Graphene epitaxy on germanium by chemical vapor deposition is a promising approach to integrate graphene into microelectronics, but the synthesis is still accompanied by several challenges such as the high process temperature, the reproducibility of growth, and the formation of etch pits during the process
We show that the substrate cleaning by preannealing in molecular hydrogen, which is crucial to successful and reproducible graphene growth, requires a high temperature and dose
Summary
The unique properties of graphene, such as its flat form factor, its high carrier mobility, its tunable Fermi level, and its plasmonic activity, make this material a candidate for a variety of applications in microelectronics, such as radiofrequency electronics,[1] optoelectronics,[2,3,4] and chemical sensing.[5]. Further integration approaches are the transfer by bonding of a graphene-covered wafer to the target wafer[9,10] and the direct synthesis on the target wafer. For all these integration schemes, germanium is a promising substrate because it can be grown epitaxially on silicon, and waferscale graphene growth on germanium from a mixture of hydrogen and methane has been demonstrated.[11–13]. To date, accompanying challenges are the poor electrical quality of gr/Ge(001),[12] the faceting of the substrate under gr/Ge(001),[14,15] and the high synthesis temperature. To solve these challenges, a better understanding of the growth process is necessary. In this paper, we present basic aspects of gr/Ge(001) synthesis, focusing on substrate cleaning and how etch pits can form during cleaning and subsequent graphene growth
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