Semiconductor heterostructures with modulated composition and/or doping enable passivation of interfaces and the generation of devices with diverse functions. In this regard, the control of interfaces in nanoscale building blocks with high surface area will be increasingly important in the assembly of electronic and photonic devices. Core-shell heterostructures formed by the growth of crystalline overlayers on nanocrystals offer enhanced emission efficiency, important for various applications. Axial heterostructures have also been formed by a one-dimensional modulation of nanowire composition and doping. However, modulation of the radial composition and doping in nanowire structures has received much less attention than planar and nanocrystal systems. Here we synthesize silicon and germanium core-shell and multishell nanowire heterostructures using a chemical vapour deposition method applicable to a variety of nanoscale materials. Our investigations of the growth of boron-doped silicon shells on intrinsic silicon and silicon-silicon oxide core-shell nanowires indicate that homoepitaxy can be achieved at relatively low temperatures on clean silicon. We also demonstrate the possibility of heteroepitaxial growth of crystalline germanium-silicon and silicon-germanium core-shell structures, in which band-offsets drive hole injection into either germanium core or shell regions. Our synthesis of core-multishell structures, including a high-performance coaxially gated field-effect transistor, indicates the general potential of radial heterostructure growth for the development of nanowire-based devices.

https://cml.harvard.edu/assets/nature420_57.pdf

Epitaxial core–shell and core–multishell nanowire heterostructures

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

Zinc oxide (ZnO) is a wide band gap semiconductor with potential applications in optoelectronics, transparent electronics, and spintronics. The high efficiency of UV emission in this material could be harnessed in solid-state white lighting devices. The problem of defects, in particular, acceptor dopants, remains a key challenge. In this review, defects in ZnO are discussed, with an emphasis on the physical properties of point defects in bulk crystals. As grown, ZnO is usually n-type, a property that was historically ascribed to native defects. However, experiments and theory have shown that O vacancies are deep donors, while Zn interstitials are too mobile to be stable at room temperature. Group-III (B, Al, Ga, and In) and H impurities account for most of the n-type conductivity in ZnO samples. Interstitial H donors have been observed with IR spectroscopy, while substitutional H donors have been predicted from first-principles calculations but not observed directly. Despite numerous reports, reliable p-t...

Defects in ZnO

The fact that wide bandgap semiconductors are capable of electronic functionality at much higher temperatures than silicon has partially fueled their development, particularly in the case of SiC. It appears unlikely that wide bandgap semiconductor devices will find much use in low-power transistor applications until the ambient temperature exceeds approximately 300/spl deg/C, as commercially available silicon and silicon-on-insulator technologies are already satisfying requirements for digital and analog VLSI in this temperature range. However practical operation of silicon power devices at ambient temperatures above 200/spl deg/C appears problematic, as self-heating at higher power levels results in high internal junction temperatures and leakages. Thus, most electronic subsystems that simultaneously require high-temperature and high-power operation will necessarily be realized using wide bandgap devices, once they become widely available. Technological challenges impeding the realization of beneficial wide bandgap high ambient temperature electronics, including material growth, contacts, and packaging, are briefly discussed.

High-temperature electronics - a role for wide bandgap semiconductors?

A high quality single crystal wafer of SiC is disclosed having a diameter of at least about 100mm and a micropipe density of less than about 25 cm-2.

100 mm silicon carbide wafer with low micropipe density

Verfahren zur Herstellung 100mm Siliciumkarbidwafer mit geringer Mikroröhrchendichte

La presente invention concerne un cristal semiconducteur et un procede de tirage associe. Le cristal comprend une partie germe et une partie tiree sur la partie germe. La partie germe et la partie tiree forment un monocristal de carbure de silicium cylindrique pratiquement droit. Une face du germe definit une interface entre la partie tiree et la partie germe, ladite face du germe etant pratiquement parallele aux bases du cristal cylindrique droit et etant excentree par rapport au plan basal du monocristal. La partie tiree reproduit le polytype de la partie germe et la partie tiree a un diametre d'au moins 100 mm environ.

CRISTAL DE SiC DE CENT MILLIMÈTRES TIRÉ SUR UN GERME DÉCALÉ

A silicon carbide seeded sublimation growth system and associated method are disclosed. The system includes a crucible, a silicon carbide source composition in the crucible, a seed holder in the crucible, a silicon carbide seed crystal on the seed holder, means for creating a major thermal gradient in the crucible that defines a major growth direction between the source composition and the seed crystal for encouraging vapor transport between the source composition and the seed crystal, and the seed crystal being positioned on the seed holder with the macroscopic growth surface of the seed crystal forming an angle of between about 70° and 89.5° degrees relative to the major thermal gradient and the major growth direction and with the crystallographic orientation of the seed crystal having the c-axis of the crystal forming an angle with the major thermal gradient of between about 0° and 2°.

Method and system with seed holder for growing silicon carbide single crystals

PROBLEM TO BE SOLVED: To provide a method for manufacturing a silicon carbide bulk single crystal wherein the crystal formed by a sublimation system using a seed crystal in order to reduce the total number of defects in the manufactured crystal has a low 1c screw dislocation level, a larger size and a high quality. SOLUTION: The high quality SiC single crystal wafer is a polytype selected from the group consisting of 3C, 4H, 6H, 2H and 15R polytypes and has a diameter of at least 76.2 mm (about 3 in.) and a 1c screw dislocation density of less than about 2,000 cm -2 . COPYRIGHT: (C)2009,JPO&INPIT

Adrian Powell

Papers

100 mm silicon carbide wafer with low micropipe density

Verfahren zur Herstellung 100mm Siliciumkarbidwafer mit geringer Mikroröhrchendichte

CRISTAL DE SiC DE CENT MILLIMÈTRES TIRÉ SUR UN GERME DÉCALÉ

Method and system with seed holder for growing silicon carbide single crystals

3 inch silicon carbide wafer having low 1c screw dislocation