We present the science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems, targeting an evolution in technology, that might lead to impacts and benefits reaching into most areas of society. This roadmap was developed within the framework of the European Graphene Flagship and outlines the main targets and research areas as best understood at the start of this ambitious project. We provide an overview of the key aspects of graphene and related materials (GRMs), ranging from fundamental research challenges to a variety of applications in a large number of sectors, highlighting the steps necessary to take GRMs from a state of raw potential to a point where they might revolutionize multiple industries. We also define an extensive list of acronyms in an effort to standardize the nomenclature in this emerging field.

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Science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems

A detailed review of the literature for the last 5-10 years on epitaxial growth of graphene is presented. Both experimental and theoretical aspects related to growth on transition metals and on silicon carbide are thoroughly reviewed. Thermodynamic and kinetic aspects of growth on all these materials, where possible, are discussed. To make this text useful for a wider audience, a range of important experimental techniques that have been used over the last decade to grow (e.g. CVD, TPG and segregation) and characterize (STM, LEEM, etc.) graphene are reviewed, and a critical survey of the most important theoretical techniques is given. Finally, we critically discuss various unsolved problems related to growth and its mechanism which we believe require proper attention in future research.

/pdf/growth-of-epitaxial-graphene-theory-and-experiment-5btol43yrq.pdf

Growth of Epitaxial Graphene: Theory and Experiment

Very slow drain current and surface potential transients have been observed in AlGaN/GaN heterostructure field effect transistors that are subjected to high bias stress. Simultaneous measurements of drain current and surface potential indicate that large change in surface potential after stress is responsible for the reduction in drain current in these devices. Measurements of surface potential profile from the gate edge toward the drain as a function of time indicate that surface potential changes occur mostly near the gate. It is proposed that the surface potential changes are caused by electrons which tunnel from the gate under high bias stress and get trapped at the surface states near the gate. Passivation of the surface with SiN/sub x/ reduces the transient magnitudes to a large extent. This correlates with a large improvement in microwave power performance in these devices after passivation. UV illumination of these devices totally eliminates the drain current and surface potential transients.

Slow transients observed in AlGaN/GaN HFETs: effects of SiN/sub x/ passivation and UV illumination

Growth of epitaxial graphene: Theory and experiment

Graphene has a multitude of striking properties that make it an exceedingly attractive material for various applications, many of which will emerge over the next decade. However, one of the most promising applications lie in exploiting its peculiar electronic properties which are governed by its electrons obeying a linear dispersion relation. This leads to the observation of half integer quantum hall effect and the absence of localization. The latter is attractive for graphene-based field effect transistors. However, if graphene is to be the material for future electronics, then significant hurdles need to be surmounted, namely, it needs to be mass produced in an economically viable manner and be of high crystalline quality with no or virtually no defects or grains boundaries. Moreover, it will need to be processable with atomic precision. Hence, the future of graphene as a material for electronic based devices will depend heavily on our ability to piece graphene together as a single crystal and define its edges with atomic precision. In this progress report, the properties of graphene that make it so attractive as a material for electronics is introduced to the reader. The focus then centers on current synthesis strategies for graphene and their weaknesses in terms of electronics applications are highlighted.

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Graphene: Piecing it together.

A betavoltaic cell in 4H SiC is demonstrated. A p-n diode structure was used to collect the charge from a 1mCi Ni-63 source. An open circuit voltage of 0.72V and a short circuit current density of 16.8nA∕cm2 were measured in a single p-n junction. A 6% lower bound on the power conversion efficiency was obtained. A simple photovoltaic-type model was used to explain the results. Fill factor and backscattering effects were included in the efficiency calculation. The performance of the device was limited by edge recombination.

Demonstration of a 4H SiC betavoltaic cell

Epitaxial growth of graphitic carbon on C-face SiC and sapphire by chemical vapor deposition (CVD)

Surface effects on the current instability of 4H-SiC MESFETs were studied by comparing different surface structures. The current instability phenomenon was illustrated by bias sweeping methods and current recovery time measurements. A reduction in the current instability was observed for gate-recessed and buried-gate devices compared to the nonrecessed and channel-recessed devices. In addition, the buried-gate devices were found to have higher current density and breakdown voltage compared to the gate-recessed devices, resulting from their shorter effective gate length and lower electric field distribution under the gate, respectively. With high saturation current, high breakdown voltage, and much reduced surface effects, the buried-gate structure is a candidate for high-power SiC MESFETs.

Reduced trapping effects and improved electrical performance in buried-gate 4H-SiC MESFETs

A betavoltaic cell in 4H SiC is demonstrated. An abrupt p-n diode structure was used to collect the charge from a 1mCi Ni-63 source. An open circuit voltage of 0.95V and a short circuit current density of 8.8 nA/cm2 were measured in a single p-n junction. An efficiency of 3.7% was obtained. A simple photovoltaic type model was used to explain the results. Good correspondence with the model was obtained. Fill factor and backscattering effects were included. Efficiency was limited by edge recombination and poor fill factor.

Demonstration of a 4H SiC Betavoltaic Cell

We report on very long surface potential transients induced by ultraviolet laser illumination, which have been observed in nitride heterostructures. These surface potential transients correlate with current transients when measured simultaneously. Under illumination, electron–hole pairs are generated, which screen the electric field in the AlGaN barrier layer causing the surface potential to decrease. The holes move toward the surface assisted by the electric field in the AlGaN while the electrons increase the sheet charge concentration at the AlGaN/GaN interface, decreasing the net charge dipole across the barrier layer. This reduction can cause the surface potential to vary as much as 1 V between the unilluminated and illuminated states. The long transient response observed after the laser is turned off is explained by the slow recombination of the holes with the electrons thermionically emitted from the potential well at the interface. The thermionic emission is modeled by a continuously varying barrie...

Laser-induced surface potential transients observed in III-nitride heterostructures

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