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The luminescence properties of cubic GaN films grown upon 3C-SiC/Si (001) substrates by MOCVD were investigated. The spectra show luminescence peaks which are associated with donor bound exciton recombination and donor acceptor pair recombination. A reduced peak energy for the D0X emission compared with values reported in the literature suggests a tensile-strain-reduced bandgap of approximately 3.27 eV, which is consistent with the absorption edge in photoluminescence-excitation spectroscopy. The presence of hexagonal material introduces a broad emission band at 3.40 eV with a FWHM of 190 meV, extending to energies up to 3.60 eV. The intensity of this emission scales linearly with excitation power, its peak energy and width remaining unchanged. This band is associated with an absorption edge below 3.70 eV and therefore is not caused by absorption into phase-pure cubic or hexagonal GaN. The photoluminescence lifetimes measured across this band reduce from 0.40 to 0.20 ns with increasing emission energy. All these observations can be explained by considering a type-II-band alignment adjacent to stacking faults within the cubic GaN. [ABSTRACT FROM AUTHOR]

The chemical reactions that take place at surfaces as well as internally in nanoscale particles are of great scientific interest. Such reactions control the catalytic properties of small metal particles and thus are technologically very important. In order to allow enhancement of the performance of such catalytic systems, an understanding of the processes taking place at the atomic scale is necessary. Z-contrast imaging and electron energy-loss spectroscopy (EELS) in the dedicated scanning transmission electron microscope can give atomic-scale information and thus provide a unique opportunity to study such nanoscale systems. Here, iron particles from known positions in a ferrocene-seeded flame and their effects on soot formation are studied. Using EELS, spatial variations in oxidation state of the metal atoms are detected across individual nanometre-sized particles collected from the post-flame region. The surfaces of these particles are found to be less oxidized than their centres. Additionally, the particles are imaged with atomic resolution allowing their structure to be identified. Using these results and those for particles collected from in-flame regions, direct evidence is provided for the catalytic role of Fe-containing particles in the removal of carbonaceous soot produced during combustion of hydrocarbon-based fuels. [ABSTRACT FROM AUTHOR]

The impact of the stress in room temperature inductively coupled plasma chemical vapour deposited (ICP-CVD) SiNx surface passivation layers on off-state drain (IDS-off) and gate leakage currents (IGS) in AlGaN/GaN high electron mobility transistors (HEMTs) is reported. IDS-off and IGS in 2 μm gate length devices were reduced by up to four orders of magnitude to ~10 pA/mm using a compressively stressed bilayer SiNx passivation scheme. In addition, Ion/Ioff of ~1011 and subthreshold slope of 68 mV/dec were obtained using this strain engineered surface passivation approach. [ABSTRACT FROM AUTHOR]