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

In the past several years, research in each of the wide‐band‐gap semiconductors, SiC, GaN, and ZnSe, has led to major advances which now make them viable for device applications. The merits of each contender for high‐temperature electronics and short‐wavelength optical applications are compared. The outstanding thermal and chemical stability of SiC and GaN should enable them to operate at high temperatures and in hostile environments, and also make them attractive for high‐power operation. The present advanced stage of development of SiC substrates and metal‐oxide‐semiconductor technology makes SiC the leading contender for high‐temperature and high‐power applications if ohmic contacts and interface‐state densities can be further improved. GaN, despite fundamentally superior electronic properties and better ohmic contact resistances, must overcome the lack of an ideal substrate material and a relatively advanced SiC infrastructure in order to compete in electronics applications. Prototype transistors have been fabricated from both SiC and GaN, and the microwave characteristics and high‐temperature performance of SiC transistors have been studied. For optical emitters and detectors, ZnSe, SiC, and GaN all have demonstrated operation in the green, blue, or ultraviolet (UV) spectra. Blue SiC light‐emitting diodes (LEDs) have been on the market for several years, joined recently by UV and blue GaN‐based LEDs. These products should find wide use in full color display and other technologies. Promising prototype UV photodetectors have been fabricated from both SiC and GaN. In laser development, ZnSe leads the way with more sophisticated designs having further improved performance being rapidly demonstrated. If the low damage threshold of ZnSe continues to limit practical laser applications, GaN appears poised to become the semiconductor of choice for short‐wavelength lasers in optical memory and other applications. For further development of these materials to be realized, doping densities (especially p type) and ohmic contact technologies have to be improved. Economies of scale need to be realized through the development of larger SiC substrates. Improved substrate materials, ideally GaN itself, need to be aggressively pursued to further develop the GaN‐based material system and enable the fabrication of lasers. ZnSe material quality is already outstanding and now researchers must focus their attention on addressing the short lifetimes of ZnSe‐based lasers to determine whether the material is sufficiently durable for practical laser applications. The problems related to these three wide‐band‐gap semiconductor systems have moved away from materials science toward the device arena, where their technological development can rapidly be brought to maturity.

Large‐band‐gap SiC, III‐V nitride, and II‐VI ZnSe‐based semiconductor device technologies

Wide bandgap semiconductors are extremely attractive for the gamut of power electronics applications from power conditioning to microwave transmitters for communications and radar. Of the various materials and device technologies, the AlGaN/GaN high-electron mobility transistor seems the most promising. This paper attempts to present the status of the technology and the market with a view of highlighting both the progress and the remaining problems.

AlGaN/GaN HEMTs-an overview of device operation and applications

Wide bandgap semiconductors show superior material properties enabling potential power device operation at higher temperatures, voltages, and switching speeds than current Si technology. As a result, a new generation of power devices is being developed for power converter applications in which traditional Si power devices show limited operation. The use of these new power semiconductor devices will allow both an important improvement in the performance of existing power converters and the development of new power converters, accounting for an increase in the efficiency of the electric energy transformations and a more rational use of the electric energy. At present, SiC and GaN are the more promising semiconductor materials for these new power devices as a consequence of their outstanding properties, commercial availability of starting material, and maturity of their technological processes. This paper presents a review of recent progresses in the development of SiC- and GaN-based power semiconductor devices together with an overall view of the state of the art of this new device generation.

A Survey of Wide Bandgap Power Semiconductor Devices

An object is to provide a semiconductor device of which a manufacturing process is not complicated and by which cost can be suppressed, by forming a thin film transistor using an oxide semiconductor film typified by zinc oxide, and a manufacturing method thereof. For the semiconductor device, a gate electrode is formed over a substrate; a gate insulating film is formed covering the gate electrode; an oxide semiconductor film is formed over the gate insulating film; and a first conductive film and a second conductive film are formed over the oxide semiconductor film. The oxide semiconductor film has at least a crystallized region in a channel region.

Semiconductor device, and manufacturing method thereof

A semiconductor device includes a vertical field-effect-transistor (FET) and a bypass diode. The vertical FET device includes a substrate, a drift layer formed over the substrate, a gate contact and a plurality of source contacts located on a first surface of the drift layer opposite the substrate, a drain contact located on a surface of the substrate opposite the drift layer, and a plurality of junction implants, each of the plurality of junction implants laterally separated from one another on the surface of the drift layer opposite the substrate and extending downward toward the substrate. Each of the one or more bypass diodes are formed by placing a Schottky metal contact on the first surface of the drift layer, such that each Schottky metal contact runs between two of the plurality of junction implants.

Layout configurations for integrating schottky contacts into a power transistor device

High-Power P-Channel UMOS IGBT's in 6H-SiC for High Temperature Operation

We present a survey of the most important factors relating to an epitaxial SiC growth process that is suitable for bipolar power devices. During the last several years, we have advanced our hot-wall SiC epitaxial growth technology to the point that we can support the transition of bipolar power devices from demonstrations to applications. Two major concerns in developing a suitable epitaxial technology are epilayer uniformity and extended defect density. Our state-of-theart capability permits the realization of 1-cm2 area devices with exceptional yields. Another major concern is the stability of bipolar devices during forward conduction. We have developed proprietary substrate and epilayer preparation technologies that have essentially eliminated Vf drift as a significant barrier to the exploitation of SiC based bipolar devices.

Development of Epitaxial SiC Processes Suitable for Bipolar Power Devices

The turn-on process in 4H-SiC thyristors with a forward blocking voltage U/sub h//spl sime/400 V has been investigated in the temperature range 160-500 K. The time constant of the current rise /spl tau//sub r/ decreases monotonically with temperature, increasing from /spl tau//sub r//spl sime/63 ns at T=160 K to /spl tau//sub r/=1.9 ns at T=495 K.

Temperature dependence of turn-on process in 4H-SiC thyristors

Initial results from a custom, 3x150 mm horizontal hot-wall, SiC Vapor-Phase epitaxial growth reactor (VPE), with full planetary motion are reported. Epitaxial layer properties are compared with those grown on previously reported 1x150 mm hot-wall and 6x150 mm warm-wall reactors for epitaxial wafers of up to 100 microns thickness. The median intra-wafer thickness and doping uniformity (σ/mean) for the 3x150 mm reactor are 0.9% and 6.10%, respectively. The intra-run thickness and doping variation are 0.18% and 1.01%. The projected 5x5 mm useable area for layers of nominal 5 to 30 μm thickness for all the reactor configurations (as measured by a Candela CS2 optical surface analyzer) are approximately 92%, corresponding to an effective defect density of about 0.35 cm-2. Useable areas as high as 86.5% and 1-2 nm rms roughness have been observed for layers of over 100 μm thickness. Initial morphological results using a higher resolution, LaserTec SICA6X confocal differential interference contrast (CDIC) microscope, are also presented.

John W. Palmour

Papers

Layout configurations for integrating schottky contacts into a power transistor device

High-Power P-Channel UMOS IGBT's in 6H-SiC for High Temperature Operation

Development of Epitaxial SiC Processes Suitable for Bipolar Power Devices

Temperature dependence of turn-on process in 4H-SiC thyristors

Advances in 3x150 mm Hot-Wall and 6x150 mm Warm-Wall SiC Epitaxy for 10kV-Class Power Devices