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Graphene

 

 

Molecular dynamic calculations of graphene grown on a van-der Waals insulator. The mobility of graphene on insulating van der Waals substrates is shown, as it moves like a magic carpet across the substrate without interacting. The wobbling of graphene and substrate is caused by the applied temperature of 700°C.

Graphene growth

 

To enable application of graphene in future high frequency electronic devices a Si technology-compatible graphene synthesis method on Si substrate platform is required. While for some devices it would be of advantage to isolate graphene from the Si substrate with a layer of a high bang gap dielectric (e.g. SiO2), other device concepts require graphene to be deposited directly on a semiconductor (e.g. Ge or Si).

 

To satisfy these requirements and enable fabrication of graphene-based devices using tools and processes compatible with standard Si processing we focus on two different approaches to graphene synthesis. In the first approach, a catalytically active Ni film is grown on SiO2/Si(100) substrates and patterned into wire-like structures (Fig. 3 a). These metal lines serve as seeds for the growth of graphene directly on SiO2. In the second approach, a single-crystalline Ge(100) layer is firstly grown on blanket or patterned Si(100) wafers. In this way prepared samples serve as substrates for direct graphene growth on Ge surfaces from solid and gas carbon sources (Fig. 3 b).

Fig. 3: Two approaches to direct growth of graphene on insulating and semiconducting substrates: Ni-assisted growth on SiO2 (a) and direct growth on Ge surfaces (b).

Graphene growth experiments are performed in two separate chambers (Fig. 4) connected to each other and to an analysis chamber via UHV buffer lines. This setup allows for in-situ control of the growth process using XPS and UPS. Figure 5 shows an example of ex-situ Raman characterization for graphene layers grown directly on Ge/Si(100) substrates [4].

Fig. 4: MBE chamber with a solid state carbon source (left) and gas-source MBE chamber dedicated

to catalytic growth of graphene on insulators (right).

Fig. 5: Raman spectroscopy investigation of graphene grown on patterned Ge/Si(100) substrates.

To gain more insight into the growth process of graphene on dielectric and semiconducting surfaces, molecular dynamic simulations based on density functional theory are applied. These simulations provide additionally a valuable feedback enabling optimization of the substrate preparation and graphene deposition conditions.

The building and the infrastructure of the IHP were funded by the European Regional Development Fund of the European Union, funds of the Federal Government and also funds of the Federal State of Brandenburg.