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

SiC device technology: remaining issues

An overview of the status of SiC technology for power devices is discussed. 4H-SiC is the most desirable SiC polytype for power devices because of its superior electron transport properties. Micropipe defect densities in 4H-SiC have been dramatically reduced, with 0.8 cm/sup -2/ being demonstrated on a 35 mm wafer. Interface trap densities of 1/spl times/10/sup 11/ cm/sup -2/ eV/sup -1/ at the oxide/SiC interface have been achieved, resulting in a high SiC NMOSFET channel mobility of 72 cm/sup 2//V-sec. Device lifetimes for SiC n-channel MOSFETs have are projected to be 5 years at 350/spl deg/C, and time dependent dielectric breakdown of oxides on p-type SiC have lifetimes >700 years at 2 MV/cm and 350/spl deg/C. Sheet resistivities of <10 k/spl Omega//sq. and p-type contact resistivities less than 10/sup -5/ /spl Omega/-cm/sup 2/ have been obtained using high temperature Al/sup +/ ion implantation, and the first SiC CMOS circuits have been demonstrated using this technology. Power MOSFETs in 4H-SiC have been demonstrated to have specific on-resistances lower than equivalent Si devices, and blocking voltages as high as 800 V have been achieved. The highest power devices to date are 4.2 kW, 700 V 4H-SiC npnp thyristors, and their speed is very high, with a t/sub rr/=105 nsecs and maximum operating frequency of 250 kHz.

Silicon carbide for power devices

Steady-state and transient forward current-voltage I-V characteristics have been measured in 55 kV p/sup +/-n-n/sup +/ 4H-SiC rectifier diodes up to a current density j/spl ap/55/spl times/10/sup 4/ A/cm/sup 2/ The steady-state data are compared with calculations in the framework of a model, in which the emitter injection coefficient decreases with increasing current density To compare correctly the experimental and theoretical results, the lifetime of minority carriers for high injection level, /spl tau//sub ph/, has been estimated from transient characteristics At low injection level, the hole diffusion length L/sub pl/ has been measured by photoresponse technique For a low-doped n-base, the hole diffusion lengths are L/sub pl//spl ap/2 /spl mu/m and L/sub ph//spl ap/6-10 /spl mu/m at low and high injection levels respectively Hole lifetimes for low and high injection levels are /spl tau//sub pl//spl ap/15 ns and /spl tau//sub ph//spl ap/140-400 ns The calculated and experimental results agree well within the wide range of current densities 10 A/cm/sup 2/ 5 kA/cm/sup 2/, the experimental values of residual voltage drop V is lower than the calculated ones In the range of current densities 5/spl times/10/sup 3/ A/cm/sup 2/ 25 kA/cm/sup 2/, R/sub d/ increases with increasing current density manifesting the contribution of other nonlinear mechanisms to the formation steady-state current-voltage characteristic The possible role of Auger recombination is also discussed

Steady-state and transient forward current-voltage characteristics of 4H-silicon carbide 5.5 kV diodes at high and superhigh current densities

A 2-mm/spl times/2-mm, 4H-SiC, asymmetrical npnp gate turn-off (GTO) thyristor with a blocking voltage of 3100 V and a forward current of 12 A is reported. This is the highest reported power handling capability of 37 kW for a single device in SiC. The 5-epilayer structure utilized a blocking layer that was 50 /spl mu/m thick, p-type, doped at about 7-9/spl times/10/sup 14/ cm/sup -3/. The devices were terminated with a single zone junction termination extension (JTE) region formed by ion-implantation of nitrogen at 650/spl deg/C. The device was able to reliably turn-on and turn-off 20 A (500 A/cm/sup 2/) of anode current with a turn-on gain (I/sub K//I/sub G, on/) of 20 and a turn-off gain (I/sub K//I/sub G, off/) of 3.3.

John W. Palmour

Papers

SiC device technology: remaining issues

Silicon carbide for power devices

Steady-state and transient forward current-voltage characteristics of 4H-silicon carbide 5.5 kV diodes at high and superhigh current densities

3100 V, asymmetrical, gate turn-off (GTO) thyristors in 4H-SiC

High Temperature, High Current, 4H-SiC Accu-DMOSFET