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Measurements of the dark conductivity and thermoelectric power in hydrogenated amorphous silicon–germanium alloys (a-Si1-xGex:H) reveal that charge transport is not well described by an Arrhenius expression. For alloys with concentrations of Ge below 20%, anomalous hopping conductivity is observed with a power-law exponent of 3/4, while the temperature dependence of the conductivity of alloys with higher Ge concentrations is best fit by a combination of anomalous hopping and a power-law temperature dependence. The latter has been attributed to charge transport via multi-phonon hopping. Corresponding measurements of the Seebeck coefficient reveal that the thermopower is n-type for the purely a-Si:H and a-Ge:H samples but that it exhibits a transition from negative to positive values as a function of the Ge content and temperature. These findings are interpreted in terms of conduction via hopping through either exponential band tail states or dangling bond defects, suggesting that the concept of a mobility edge, accepted for over five decades, may not be necessary to account for charge transport in amorphous semiconductors. [ABSTRACT FROM AUTHOR]

In this paper, we present a large-volume (non-micro) atmospheric pressure glow plasma capable of rapid, large-scale zinc oxide nanocrystal synthesis and deposition (up to 400 μg/min), whereas in the majority of the literature, nanoparticles are synthesized using micro-scale or filamentary plasmas. The reactor is an RF dielectric barrier discharge with a non-uniform gap spacing. This design encourages pre-ionization during the plasma breakdown, making the discharge uniform over a large volume. The produced zinc oxide nanocrystals typically have diameters ranging from 4 to 15nm and exhibit photoluminescence at ≈550 nm and localized surface plasmon resonance at ≈1900 cm-1 due to oxygen vacancies. The particle size can be tuned to a degree by varying the gas temperature and the precursor mixing ratio. [ABSTRACT FROM AUTHOR]

Langmuir probe estimation of the axial and radial distribution of electron distribution function (EDF) shows that EDF is a spatially homogeneous electron energy function. A one-dimensional model for the axial distribution involves a nonlocal solution for the spatially inhomogeneous Boltzmann equation. Theoretical and experimental EDF estimates are consistent.

A dual-plasma codeposition system capable of synthesizing thin films of mixed-phase materials consisting of nanoparticles of one type of material embedded within a thin film semiconductor or insulator matrix is described. This codeposition process is illustrated by the growth of hydrogenated amorphous silicon (a-Si:H) films containing silicon nanocrystalline inclusions (a/nc-Si:H). A capacitively coupled flow-through plasma reactor is used to generate silicon nanocrystallites of diameter 5 nm, which are entrained by a carrier gas and introduced into a capacitively coupled plasma enhanced chemical vapor deposition reactor with parallel plate electrodes, in which a-Si:H is synthesized. The structural and electronic properties of these mixed-phase a/nc-Si:H films are investigated as a function of the silicon nanocrystal concentration. At a moderate concentration (crystalline fraction 0.02–0.04) of silicon nanocrystallites, the dark conductivity is enhanced by up to several orders of magnitude compared to mixed-phase films with either lower or higher densities of nanoparticle inclusions. These results are interpreted in terms of a model whereby in films with a low nanocrystal concentration, conduction is influenced by charges donated into the a-Si:H film by the inclusions, while at high nanocrystal densities electronic transport is affected by increased disorder introduced by the nanoparticles. [ABSTRACT FROM AUTHOR]

The growth of silicon oxide on bare and SF6-etched silicon nanocrystals (Si-NCs), which were synthesized by an all gas phase approach, was investigated by examining the surface chemistry and optical properties of the NCs over time. Consistent with previous work in the low temperature oxidation of silicon, the oxidation follows the Cabrera–Mott mechanism, and the measured data are well fitted to the Elovich equation. The use of the SF6 plasma is found to reduce the surface Si–H bond density and dramatically increase the monolayer growth rate. This is believed to be due to the much larger volatility of Si–F bonds compared to Si–H bonds on the surface of the NC. [ABSTRACT FROM AUTHOR]

Electrical contact to amorphous silicon nanoparticles was established with a method that self aligns the contacts to the particles. Charge transport characteristics were studied as a function of temperature and voltage. The conduction in these devices was not limited by the metal/semiconductor barrier; rather it was limited by charge trapping in the particles themselves. The data are well fit to theory. It was shown that the space charge limited current (SCLC) model fits the medium voltage range (2–6 V), while space charged limited current with Frenkel–Poole effect fits the relatively high voltage range (5–8 V). Using a model for space charge limited current in the presence of an exponential distribution of traps, we estimate that the trap density is 2×1019 cm-3. Based on SCLC enhanced with Frenkel–Poole effect, the activation energy measured at high voltage was determined to 0.44 eV. This agrees well with the medium voltage activation energy, 0.41 eV. [ABSTRACT FROM AUTHOR]

We have investigated silicon particles formed in an inductively coupled plasma (ICP) system and have measured their structural properties by electron microscopy. ICP silane plasmas are shown to be an interesting and versatile source of nanoparticles. Three regimes are mapped out: a regime of no observable particle growth at the lowest pressures, a regime of polydisperse and agglomerated particles at the highest pressures, and a regime yielding highly monodisperse particles at intermediate pressures. Our results suggest that an ICP allows this unique production of monodisperse nanoparticles at high concentrations. The particle size can be controlled from 15 to 200 nm and is determined by the plasma on time. For short plasma times, particle growth appears to be due primarily to coagulation, while in the second phase particle growth is attributed primarily to surface deposition. For H[SUB2] dilutions less than 92%, the growth rate is almost independent of H[SUB2] partial pressure. Transmission electron micrographs, however, indicate that the addition of hydrogen decreases the particle density. At higher dilution ratios, polycrystalline particles are obtained. Under all other conditions the particles are amorphous. [ABSTRACT FROM AUTHOR]

The carrier transport mechanisms in amorphous silicon nanoparticles are examined. The temperature dependence of the current voltage (I-V) measurements is studied and the mechanism of carrier transport is proposed.

A study was conducted to investigate the time dependence of the spectral emission of an atmospheric pressure glow discharge in helium with impurities with a two-dimensional spatial resolution. The results indicate a radial spreading of the discharge during the current pulse as well as the formation of a ring-like, radially propagating cathode layer late in the current pulse.

The silicon particles formed in an inductively coupled plasma (ICP) system are studied. Results indicate that at higher dilution ratios, polycrystalline particles are obtained,

Studies the radiative efficiency of the 147 nanometer resonance radiation of xenon excited in a low pressure, high frequency surface wave sustained in plasma. Optical absorption spectroscopic measurements; Monte Carlo calculations of the effective decay rate; Efficiencies.