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?

SiGe/Si quantum wells with abrupt interfaces grown by atmospheric pressure chemical vapor deposition

Experimental results are presented for SiC epitaxial layer growth employing a large-area, up to 8x100-mm, warm-wall planetary SiC-VPE reactor. This high-throughput reactor has been optimized for the growth of uniform 0.01 to 80-micron thick, specular, device-quality SiC epitaxial layers with low background doping concentrations of 1x1019 cm-3. Intrawafer layer thickness and n-type doping uniformity (σ/mean) of ~2% and ~8% have been achieved to date in the 8x100-mm configuration. The total range of the average intrawafer thickness and doping within a run are approximately ±1% and ±6% respectively.

SiC Warm-Wall Planetary VPE Growth on Multiple 100-mm Diameter Wafers

First structural and electrical data are reported for SiGe/Si quantum well structures grown by a new ultra clean low temperature epitaxial deposition process at atmospheric pressure. It is found that the process suppresses the segregation of germanium, possibly by a chemical termination of the surface during the growth. Mutiple-quantum-well structures with controllable well widths and abrupt interfaces have been prepared at temperatures ranging from 550 to 650°C. Magneto-transport measurements of modulation doped quantum wells reveal hole mobilities of 2000 cm2/Vs at 4.2 K at a carrier density of 1.7*1012 cm−2 and a germanium concentration of 18% in the SiGe channel. Resonant tunneling diodes grown by this technique exhibit well resolved regions of negative differential resistance within a very symmetric I-V characteristic.

Growth of SiGe/Si quantum well structures by atmospheric pressure chemical vapor deposition

The path to commercializing a 4H-SiC power PiN diode has faced many difficult challenges. In this work, we report a 50 A, 10 kV 4H-SiC PiN diode technology where good crystalline quality and high carrier lifetime of the material has enabled a high yielding process with V/sub F/ as low as 3.9 V @ 100 A/cm/sup 2/. These 10 kV diodes demonstrate pulsed current handling capability up to 328 A which represents over 3 MW of pulsed power. Furthermore, incorporation of two independent basal plane dislocation reduction processes (LBPD 1 and LBPD 2) have produced a large number of devices that exhibit a high degree of forward voltage stability. The more benign LBPD 2 process yields wafers with better reverse blocking capability resulting in a total yield (forward, 10 kV blocking, and drift) of >20% for 8.7 mm /spl times/ 8.7 mm power PiN diode chips - the largest SiC chip reported to date.

http://ieeexplore.ieee.org/iel5/10392/33024/01549700.pdf

Adrian Powell

Papers

SiGe/Si quantum wells with abrupt interfaces grown by atmospheric pressure chemical vapor deposition

SiC Warm-Wall Planetary VPE Growth on Multiple 100-mm Diameter Wafers

Growth of SiGe/Si quantum well structures by atmospheric pressure chemical vapor deposition

High power, drift-free 4H-SiC PiN diodes

High power, drift-free 4H-SiC PiN diodes