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 is disclosed that includes a layer of Group III nitride semiconductor material that includes at least one surface, a control contact on the surface for controlling the electrical response of the semiconductor material, a dielectric barrier layer covering at least a portion of the one surface adjacent the control contact, the dielectric barrier layer having a bandgap greater than the bandgap of the Group III nitride and a conduction band offset from the conduction band of the Group III nitride, and a dielectric protective layer covering the remainder of the Group III nitride surface.

Improved dielectric passivation for semiconductor devices

A normally-off type 5.3 kV 4H-SiC JFET with low specific on-resistance, called a SEJFET (Static Expansion channel JFET), has been fabricated. By an adoption of area-efficient cell structure and a proper JTE termination (Junction Termination Extension), high performance is realized. The specific on resistance (RonS) is 69 m/spl Omega/cm/sup 2/ and the turn off time is 47 ns. The highest current capability is 3.3 A. In all reported FETs, the SEJFET has the best trade-off between RonS and blocking voltage (BV), which is about 1/230/sup th/ lower than theoretical limit of a Si FET. Furthermore, the figure of merit (BV/sup 2//RonS) is 407MW/cm/sup 2/, and this value is the highest among reported normally off SiC FETs.

5 kV 4H-SiC SEJFET with low RonS of 69m/spl Omega/cm/sup 2/

The enabling features and performance of GaN based HEMTs as a high power, high bandwidth semiconductor technology are presented. Progress on materials development includes the development of AlGaN and AlN barrier HEMTs with room temperature electron mobility exceeding 2000 cm/sup 2//V-s. Trap free GaN HEMT devices with > 10 W/mm power density and devices with > 70 % efficiency are presented. Operation at > 200 /spl deg/C is reported. Simultaneous linearity and efficiency under class B is presented followed by discussion of mm-wave power performance. Finally, device scaling resulting in a total power > 100 Watts and GaN HEMT circuit demonstrations are presented including mm-wave amplifier with > 3 Watts at 30 GHz and 35 GHz.

AlGaN-GaN HEMTs: material, device, circuit technology and applications

The prime benefit of the SiC Schottky diode lies in its ability to switch fast (<50 ns) and with almost no reverse recovery charge. The incorporation of a SiC Schottky-type rectifier in typical power-electronic systems, such as motor drive circuits and switching power supplies, will virtually eliminate the switching losses. In the forward bias, Ti Schottky diode provides a forward current density of 100 A/cm/sup 2/ at a forward drop of 1.15 V, at room temperature. However, the low barrier height of Ti Schottky diode results in a very high room temperature leakage current density of 300 /spl mu/A/cm2 at 500 V. Furthermore, the leakage current becomes unacceptable at temperatures higher than 100/spl deg/C. A 4H-SiC merged PiN Schottky (MPS) diode uses interdigitated p/sup +/ regions between Schottky contacts to limit the electric field at the Schottky interface during the off-state operation of the device. It has a low on-state voltage drop and fast switching of a Schottky diode and offers a low off-state leakage current like the PiN diode. The on-state and off-state performance was optimized by analyzing the effect of adjacent p/sup +/ region width and spacing by 2D device simulations.

Design of dual use, high efficiency, 4H-SiC Schottky and MPS diodes

Steady-state and transient characteristics of packaged 6-kV 4H-SiC junction diodes have been investigated in the temperature range Т = 300 – 773 К. Analysis of the forward current-voltage characteristics and reverse current recovery waveforms shows that the lifetimeτ of non-equilibrium carriers in the base of the diodes steadily increases with temperature across the entire temperature interval. The rise in τ and decrease in carrier mobilities and diffusion coefficients with increasing temperature nearly compensate each other as regards their effect on the differential resistance of the diode, Rd. As a result, Rd is virtually temperature independent. An appreciable modulation of the base resistance takes place at room temperature even at a relatively small current density j of 20 A/cm2. At T = 800 K and j = 20 A/cm2, a very deep level of the base modulation has been observed. The bulk reverse current is governed by carrier generation in the space-charge region via a trap with activation energy of 1.62 eV. The surface leakage current of packaged structures does not exceed 2×10-6 А at T = 773 K and a reverse bias of 300 V.

John W. Palmour

Papers

Improved dielectric passivation for semiconductor devices

5 kV 4H-SiC SEJFET with low RonS of 69m/spl Omega/cm/sup 2/

AlGaN-GaN HEMTs: material, device, circuit technology and applications

Design of dual use, high efficiency, 4H-SiC Schottky and MPS diodes

High-temperature (up to 800 K) operation of 6-kV 4H-SiC junction diodes