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We demonstrate the isolation of two free carrier scattering mechanisms as a function of radial band bending in InN nanowires via universal mobility analysis, where effective carrier mobility is measured as a function of effective electric field in a nanowire field-effect transistor. Our results show that Coulomb scattering limits effective mobility at most effective fields, while surface roughness scattering only limits mobility under very high internal electric fields. High-energy α particle irradiation is used to vary the ionized donor concentration, and the observed decrease in mobility and increase in donor concentration are compared to Hall effect results of high-quality InN thin films. Our results show that for nanowires with relatively high doping and large diameters, controlling Coulomb scattering from ionized dopants should be given precedence over surface engineering when seeking to maximize nanowire mobility. [ABSTRACT FROM AUTHOR]

The band bending and carrier concentration profiles as a function of depth below the surface for oxidized InxGa1-xN alloys with a composition range of 0.39≤x≤1.00 are investigated using x-ray photoelectron, infrared reflection, and optical absorption spectroscopies, and solutions of Poisson’s equation within a modified Thomas–Fermi approximation. All of these InGaN samples exhibit downward band bending ranging from 0.19 to 0.66 eV and a high surface sheet charge density ranging from 5.0×1012 to 1.5×1013 cm-2. The downward band bending is more pronounced in the most In-rich InGaN samples, resulting in larger near-surface electron concentrations. [ABSTRACT FROM AUTHOR]

The morphology of GaN samples grown by plasma-assisted molecular beam epitaxy on Si(111) was systematically studied as a function of impinging Ga/N flux ratio and growth temperature (730–850 °C). Two different growth regimes were identified: compact and nanocolumnar. A growth diagram was established as a function of growth parameters, exhibiting the transition between growth regimes, and showing under which growth conditions GaN cannot be grown due to thermal decomposition and Ga desorption. Present results indicate that adatoms diffusion length and the actual Ga/N ratio on the growing surface are key factors to achieve nanocolumnar growth. [ABSTRACT FROM AUTHOR]

This work studies the effect of four different types of buffer layers on the structural and optical properties of InGaN layers grown on Si(111) substrates and their correlation with electrical characteristics. The vertical electrical conduction of n-InGaN/buffer-layer/p-Si heterostructures, with In composition near 46%, which theoretically produces an alignment of the bands, is analyzed. Droplet elimination by radical-beam irradiation was successfully applied to grow high quality InGaN films on Si substrates for the first time. Among several buffer choices, an AlN buffer layer with a thickness above 24 nm improves the structural and optical quality of the InGaN epilayer while keeping a top to bottom ohmic behavior. These results will allow fabricating double-junction InGaN/Si solar cells without the need of tunnel junctions between the two sub-cells, therefore simplifying the device design. [ABSTRACT FROM AUTHOR]

Low-temperature photoluminescence is studied in detail in GaN nanocolumns (NCs) grown by plasma-assisted molecular beam epitaxy under various conditions (substrate temperature and impinging Ga/N flux ratio). The relative intensities of the different emission lines, in particular those related to structural defects, appear to be correlated with the growth conditions, and clearly linked to the NC sample morphology. We demonstrate, in particular, that all lines comprised between 3.10 and 3.42 eV rapidly lose intensity when the growth conditions are such that the NC coalescence is reduced. The well-known line around 3.45 eV, characteristic of GaN NC samples, shows, however, a behavior that is exactly the opposite of the other lines, namely, for growth conditions leading to reduced NC coalescence, this line tends to become more prominent, thus proving to be intrinsic to individual GaN NCs. [ABSTRACT FROM AUTHOR]

This work reports on the growth by molecular beam epitaxy and characterization of InN/InGaN multiple quantum wells (MQWs) emitting at 1.5 μm. X-ray diffraction (XRD) spectra show satellite peaks up to the second order. Estimated values of well (3 nm) and barrier (9 nm) thicknesses were derived from transmission electron microscopy and the fit between experimental data and simulated XRD spectra. Transmission electron microscopy and XRD simulations also confirmed that the InGaN barriers are relaxed with respect to the GaN template, while the InN MQWs grew under biaxial compression on the InGaN barriers. Low temperature (14 K) photoluminescence measurements reveal an emission from the InN MQWs at 1.5 μm. Measurements as a function of temperature indicate the existence of localized states, probably due to InN quantum wells' thickness fluctuations as observed by transmission electron microscopy. [ABSTRACT FROM AUTHOR]

This work reports on the growth of wurtzite InN nanocolumns on A-plane GaN templates and on their structural and optical characterization by scanning and transmission electron microscopy, photoluminescence, and Raman spectroscopy. InN nanocolumns grown on A-plane substrates show sharp and pyramidal-like top surfaces that could be attributed to A-plane and M-plane facets, instead of the hexagonal top surfaces observed in nanocolumns grown on C-plane surfaces. The results of these characterization techniques show that the nanocolumns preserve the nonpolar growth orientation of the GaN templates. Good crystal quality is expected from the low temperature (13 K) photoluminescence dominant peak at 0.69 eV. [ABSTRACT FROM AUTHOR]

High quality InN nanocolumns have been grown by molecular beam epitaxy on bare and AlN-buffered Si(111) substrates. The accommodation mechanism of the InN nanocolumns to the substrate was studied by transmission electron microscopy. Samples grown on AlN-buffered Si(111) show abrupt interfaces between the nanocolumns and the buffer layer, where an array of periodically spaced misfit dislocations develops. Samples grown on bare Si(111) exhibit a thin SixNy at the InN nanocolumn/substrate interface because of Si nitridation. The SixNy thickness and roughness may affect the nanocolumn relative alignment to the substrate. In all cases, InN nanocolumns grow strain- and defect-free. [ABSTRACT FROM AUTHOR]

High-quality InN nanocolumns grown by molecular beam epitaxy on n-type Si(111) have been electrically characterized by atomic force microscopy. Current-voltage characteristics were measured on InN nanocolumns with similar heights but different diameters. The conductivity scales the nanocolumns reciprocal diameter, pointing to the nanocolumn lateral surface as the main conduction path. These results, opposing those found in undoped GaN nanocolumns where the conductivity is rather independent of the diameter (conduction through the volume), agree well with a model that predicts electron accumulation by Fermi level pinning within the conduction band on nonpolar (m plane) InN surfaces reconstructed under In-rich conditions. [ABSTRACT FROM AUTHOR]

The effects of Si doping on the growth mode and residual strain of GaN layers grown on Si(111) substrates by plasma-assisted molecular beam epitaxy are studied by Raman scattering and photoluminescence. As the Si concentration increases a progressive decrease of the high-energy E[sub 2] mode frequency is observed, together with a redshift of the excitonic emission. Both effects indicate an enhancement of the biaxial tensile strain of thermal origin for increasing doping level, which is confirmed by x-ray diffraction measurements. Beyond Si concentrations of 5x10[sup 18] cm[sup -3] both the phonon frequency and the exciton emission energy increase again. This change indicates a partial strain relaxation due to a change in the growth mode. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Transmission electron microscopy is used to investigate GaN layers grown on Si(111) substrates by plasma-assisted molecular-beam epitaxy. These layers were grown on top of different AlN buffer layers. Multiple-beam dark-field techniques applied to both cross-sectional and planar-view samples show the presence of inversion domains. These domains grow directly from the interface with the Si(111) substrate. Such observations are related, as in the case of growth on sapphire, to the symmetry difference between wurtzite and diamond. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A correction to the article "InN nanocolumns grown by plasma-assisted molecular beam epitaxy on A-plane GaN templates" that was published in the 2009 issue is presented.

We report on the fabrication and characterization of Schottky barrier photodetectors based on Si-doped Al[sub 0.35]Ga[sub 0.65]N layers grown on Si(111) substrates, for solar UV-band monitoring (λ<320 nm). The epilayers have been obtained by plasma-assisted molecular-beam epitaxy, showing a full width at half maximum of 15 arcmin in x-ray diffraction measurements. A very high visible rejection (>10[sup 4]) and a responsivity of 5 mA/W at 257 nm are reached. The detector time response is limited by the resistancexcapacitance product, with a minimum time constant of 20 ns in the zero-load-resistance limit. After photodiode voltage breakdown, the effect on the detector response is discussed. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]