GaN-based radial heterostructure nanowires grown by MBE and ALD

A combination of molecular beam epitaxy (MBE) and atomic layer deposition (ALD) was adopted to fabricate GaN-based core/shell NW structures. ALD was used to deposit a HfO2 shell of onto the MBE grown GaN NWs. Electron transparent samples were prepared by focussed ion beam methods and characterized using state-of-the-art analytical transmission and scanning transmission electron microscopy. The polycrystalline coating was found to be uniform along the whole length of the NWs. Photoluminescence and Raman spectroscopy analysis confirms that the HfO2 ALD coating does not add any structural defect when deposited on the NWs

Effects of surface plasma treatment on threshold voltage hysteresis and instability in metal-insulator-semiconductor (MIS) AlGaN/GaN heterostructure HEMTs

In a bid to understand the commonly observed hysteresis in the threshold voltage (VTH) in AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors during forward gate bias stress, we have analyzed a series of measurements on devices with no surface treatment and with two different plasma treatments before the in-situ Al2O3 deposition. The observed changes between samples were quasi-equilibrium VTH, forward bias related VTH hysteresis, and electrical response to reverse bias stress. To explain these effects, a disorder induced gap state model, combined with a discrete level donor, at the dielectric/semiconductor interface was employed. Technology Computer-Aided Design modeling demonstrated the possible differences in the interface state distributions that could give a consistent explanation for the observations

Multifractality of wavefunctions at the quantum Hall transition revisited

We investigate numerically the statistics of wavefunction amplitudes $\psi({\bf r})$ at the integer quantum Hall transition. It is demonstrated that in the limit of a large system size the distribution function of $|\psi|^2$ is log-normal, so that the multifractal spectrum $f(\alpha)$ is exactly parabolic. Our findings lend strong support to a recent conjecture for a critical theory of the quantum Hall transition.Comment: 4 pages Late

The 2018 GaN Power Electronics Roadmap

Gallium nitride (GaN) is a compound semiconductor that has tremendous potential to facilitate economic growth in a semiconductor industry that is silicon-based and currently faced with diminishing returns of performance versus cost of investment. At a material level, its high electric field strength and electron mobility have already shown tremendous potential for high frequency communications and photonic applications. Advances in growth on commercially viable large area substrates are now at the point where power conversion applications of GaN are at the cusp of commercialisation. The future for building on the work described here in ways driven by specific challenges emerging from entirely new markets and applications is very exciting. This collection of GaN technology developments is therefore not itself a road map but a valuable collection of global state-of-the-art GaN research that will inform the next phase of the technology as market driven requirements evolve. First generation production devices are igniting large new markets and applications that can only be achieved using the advantages of higher speed, low specific resistivity and low saturation switching transistors. Major investments are being made by industrial companies in a wide variety of markets exploring the use of the technology in new circuit topologies, packaging solutions and system architectures that are required to achieve and optimise the system advantages offered by GaN transistors. It is this momentum that will drive priorities for the next stages of device research gathered here

The oxidation of nickel and titanium studied by XPS and XAES

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EVALUATING THE INFLUENCE OF GROWTH PARAMETERS ON CVD DIAMOND DEPOSITION USING FACTORIAL ANALYSIS

The deposition of diamond films by low pressure CVD methods has been demonstrated using a number of thermal and plasma assisted CVD techniques. Addition of oxygen to the methane-hydrogen feedstock has been reported to improve the quality of diamond deposited and decrease the temperature at which diamond deposition is feasible. Oxygen also effects the growth rate and possibly the uniformity of the film. In this paper an experimental design methodology, factorial analysis, is presented which is, in principle, applicable to any CVD process. The factorial analysis identifies the most influential growth parameters and any interactions between independently variable parameters. The analysis has been applied to diamond growth using CH4-O2-H2 mixtures in a microwave assisted CVD process. The effect of oxygen addition on growth rate and film quality is discussed

Customised Layer Deposition for Chemical Reactor Applications

This paper discusses the development and application of an adaptive slicing algorithm for use with Digital Light Processing (DLP) for the manufacture of micro chemical reactors. Micro reactors have highly complex constructions and DLP has a proven ability to deliver features at the micro level with high accuracy. However, DLP fails to provide a truly smooth profiled surface finish which could influence fluid flow through entrance and exit apertures and along snaking micro channels. Ensuring smooth surfaces will minimise energy losses in the fluid flow path. Generally, layer based manufacturing techniques incur a trade off between build time and resolution. The algorithms used in this study attempt to mitigate this to some degree by calculating locations where high resolution is required through surface profiling techniques and adjusts the layer thickness accordingly. It is proposed that this adaptive layering technique may improve surface roughness and reduce friction related energy losses along micro channels within chemical reactor applications.Mechanical Engineerin

Internal photoemission technique for high-k oxide/semiconductor band offset determination: The influence of semiconductor bulk properties

A method for extracting energy band alignment of metal/high-k oxide/semiconductor structures from internal photoemission experiments is discussed by modeling the excitation and relaxation processes taking place in the semiconductor at photon irradiation. Classical literature data on photoemission of electrons from silicon and germanium surfaces into vacuum is compared with more recently published data on HfO2/Si and HfO2/Ge structures to identify characteristic features of photoelectric yield. We find that a dominating structure of such spectra, which often has been assumed to originate from the oxide barrier, derives from the energy dependence of absorption coefficient and mean free paths of excited electrons. Our results indicate that most IPE data on high-k oxide/silicon and germanium structures need re-interpretation