An epitaxial lift‐off (ELO) process for GaN materials has been demonstrated using bandgap‐selective photoenhanced wet etching of an InGaN release layer. This process has been applied to GaN layers grown on sapphire as well as native GaN substrates using a perforation technique to scale the process up to wafers of arbitrary size. The process has the advantage of leveraging conventional MOCVD growth to form the release layer, with minimal degradation of films grown on top of the release layer. The ELO process is non‐destructive and can enable cost reduction through reuse of the native GaN substrate after ELO. The GaN films have been characterized before and after ELO using AFM, SEM, XRD, TEM and by fabricating Schottky barrier diodes. The performance of Schottky diodes fabricated on GaN‐on‐sapphire structures was found to improve after ELO. Potential applications for this technology include GaN power and optoelectronic devices as well as flexible electronics. Shown is a 5‐micron‐thick GaN epitaxial film released from a 4‐inch sapphire substrate using perforations on a 1‐mm pitch. The yellow luminescence of the nitrogen face of the released film is visible under ultraviolet illumination.

In principle, boron (B) as a material has many excellent surface properties, including corrosion resistance, very high hardness, refractory properties, and a strong tendency to bond with most substrates. The potential technological benefits of the material have not been realized, because it is difficult to deposit it as coatings. B is difficult to evaporate, does not sputter well, and cannot be thermally sprayed. In this article, first successful deposition results from a robust system, based on the vacuum (cathodic) arc technology, are reported. Adherent coatings have been produced on 1100 Al, CP–Ti, Ti–6Al–4V, 316 SS, hard chrome plate, and 52 100 steel. Composition and thickness analyses have been performed by Rutherford backscattering spectroscopy. Hardness (H) and modules (E) have been evaluated by nanoindentation. The coatings are very pure and have properties characteristic of B suboxides. A microhardness of up to 27 GPa has been measured on a 400-nm-thick film deposited on 52 100 steel, with a corresponding modulus of 180 GPa. This gives a very high value for the H/E ratio, a figure-of-merit for impact resistance of the film. A number of applications are contemplated, including corrosion/abrasion protection for die-casting dies and improved wear resistance for biomedical implants.

Carbon, a compensator in GaN, is an inherent part of the organometallic vapor phase epitaxy (OMVPE) environment due to the use of organometallic sources. In this study, the impact of growth conditions are explored on the incorporation of carbon in GaN prepared via OMVPE on pseudo-bulk GaN wafers (in several cases, identical growths were performed on GaN-on-Al2O3 templates for comparison purposes). Growth conditions with different growth efficiencies but identical ammonia molar flows, when normalized for growth rate, resulted in identical carbon incorporation. It is concluded that only trimethylgallium which contributes to growth of the GaN layer contributes to carbon incorporation. Carbon incorporation was found to decrease proportionally with increasing ammonia molar flow, when normalized for growth rate. Ammonia molar flow divided by growth rate is proposed as a reactor independent predictor of carbon incorporation as opposed to the often-reported input V/III ratio. A low carbon concentration of 7.3 × 1014 atoms/cm3 (prepared at a growth rate of 0.57 µm/h) was obtained by optimizing growth conditions for GaN grown on pseudo-bulk GaN substrates.

Filtered cathodic arc deposition of fully ionized boron (B) was used to fill ∼2 μm wide trenches in silicon, having a depth:width ratio of up to 3:1. Optimal, void-free, infill is achieved with proper balance between deposition and self-sputtering, as controlled by the substrate bias. Previously, this technique was used to fill similar trenches with copper [O. R. Monteiro, J. Vac. Sci. Technol. B 17, 1094 (1999)]. In this work, successful extension of this process to B was found to require up to ten times higher bias voltage (up to 1000 V) for the sputtering phase and to benefit from a stronger angular dependence of self-sputtering yield for this lighter element.

The Doppler broadening of ion line profiles emitted by z-pinch plasma provides information about the thermalization of the implosion kinetic energy and the radiation efficiency of the pinch. Measurements of these line profiles are often complicated by source broadening in the instrument and opacity broadening of the emitted radiation. A high resolution concave crystal spectrometer in the Johann geometry was used to record the time averaged spectra of optically thin trace elements in the load. An imaging slit provided radially resolved but axially averaged spectra. The measurements indicate that lower ion temperatures ͑3-5 keV͒ are observed for Al wire loads on both the Saturn and Double EAGLE accelerators in the short current pulse mode ͑60-100 ns͒ than in the long pulse mode ͑125-225 ns͒ where values of 6.3-9.5 keV are observed. These values are smaller than those observed on Saturn by others. Furthermore, the wavelength at the line center of axially resolved ion line profiles on the DM-2 accelerator at Titan was observed to vary about some average value which implies an axially varying fluid motion of the plasma column transverse to the pinch axis.

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The spatial profiles of key physical variables such as electron temperature and density are crucial in determining the overall radiating efficiency of a Z pinch as well as the emitted photon energy distribution. The present work uses spatially resolved x-ray lines emitted from shots taken on the 4 MA Double EAGLE generator [C. Deeney et al., Phys. Rev. A 44, 6762 (1991)] at Maxwell Physics International to infer such profiles. The loads were arrays of 15 wires consisting of 95% Al, 5% Si, producing nearly 50 kJ of K-shell radiation with relatively long pulsewidths of 41–43 ns. It is found that the spatial profile of the He-like intercombination to resonance line ratio is critically affected by self-absorption and re-emission (scattering) of resonance line photons emitted from the hot, dense interior of the pinch. This ratio cannot be correctly interpreted without taking the scattering into account. Also, at densities somewhat lower than those achieved by these pinches, this line ratio becomes more temperature than density dependent. The inferred temperature gradient is much less steep than that which had been diagnosed previously for a pinch emitting a much shorter x-ray pulsewidth of 13 ns.

The current versus voltage (I-V) characteristics of a Ni/GaN Schottky diode are measured from 50 to 400 K and the temperature dependence of the extracted barrier heights and ideality factors is described as a consequence of lateral inhomogeneity at the metal-semiconductor (M-S) interface. It is shown that by invoking a modified log-normal distribution of barrier heights at the M-S interface, the extracted barrier height temperature dependence can be well explained. Further, it is shown that this approach can describe the voltage dependence of the lateral barrier distribution revealing that for effective barrier height values calculated at increasingly higher voltages, the distribution begins to converge on a single value of 0.77 eV. This value is in good agreement with the flat-band barrier height of 0.77±0.02 eV extracted from capacitancevoltage (C-V) measurements on the same device. The same procedure is used to describe the parallel conduction path apparent at low temperatures, revealing its behavior is indicative of an additional Schottky region with an increased density of low barriers which are more heavily perturbed by external bias. Finally, the model is successfully applied to previously published work on various Schottky diodes structures.