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Ahnood A.,University College London | Suzuki Y.,University College London | Madan A.,MVSystems Inc. | Nathan A.,University of Cambridge
Thin Solid Films | Year: 2012

The growth of low temperature silicon nitride using radio frequency (RF) plasma enhanced chemical vapour deposition (PECVD) is associated with high porosity and surface roughness due to the short surface diffusion length of adsorbed radicals during the deposition. In this work we present pulsed-RF PECVD as a means of achieving a film with smoother surface and reduced density of voids. The growth process and the longer surface diffusion length are discussed as the main reason behind improvement of film density while maintaining the substrate temperatures. The deposited films exhibit improved electrical performance with 72% reduction in breakdown probability compared with conventional continuous-wave RF PECVD films. A low interfacial defect density with a field effect mobility of 1.1 cm 2/V.s and subthreshold slope of 0.3 V/dec, was achieved when used as a gate dielectric in thin film transistors. © 2012 Elsevier B.V. All rights reserved. Source

Lee S.,University College London | Ahnood A.,University College London | Sambandan S.,Indian Institute of Science | Madan A.,MVSystems Inc. | Nathan A.,University of Cambridge
IEEE Electron Device Letters | Year: 2012

We present an analytical field-effect method to extract the density of subgap states (subgap DOS) in amorphous semiconductor thin-film transistors (TFTs), using a closed-form relationship between surface potential and gate voltage. By accounting the interface states in the subthreshold characteristics, the subgap DOS is retrieved, leading to a reasonably accurate description of field-effect mobility and its gate voltage dependence. The method proposed here is very useful not only in extracting device performance but also in physically based compact TFT modeling for circuit simulation. © 2012 IEEE. Source


Agency: National Science Foundation | Branch: | Program: SBIR | Phase: Phase II | Award Amount: 399.75K | Year: 1999


Hu J.,MVSystems Inc. | Zhu F.,MVSystems Inc. | Kunrath A.,MVSystems Inc. | Gaillard N.,Hawaii Natural Energy Institute
Materials Research Society Symposium Proceedings | Year: 2014

In this communication, we report our efforts to develop amorphous silicon carbide (a-SiC) thin film photoelectrodes integrated with Si solar cells to form a monolithic, hybrid photovoltaic (PV)/a-SiC device capable of water splitting using sunlight as the only energy source. The main photoelectrochemical (PEC) properties of both the a-SiC photoelectrode and complete hybrid device fabricated by the plasma enhanced chemical vapor deposition (PECVD) technique at low temperature (≤ 200°C) are discussed. The surface modification with metal nanoparticles, which is critical to PEC performances of the hybrid device, is also described. We show that, with the an a-SiC photoelectrode of p-i-n configuration and a high performance silicon heterojunction solar cell as driver, the photocurrent of the hybrid PV/a-SiC device has reached ∼5 mA/cm2. Additionally, the durability of such device has reached ∼800 hours in acidic electrolyte. Finally, we describe a roadmap for achieving the solar-to-hydrogen efficiency of >10% by optimizing the device configuration. Copyright © Materials Research Society 2014. Source

Kiriluk K.G.,Colorado School of Mines | Williamson D.L.,Colorado School of Mines | Bobela D.C.,National Renewable Energy Laboratory | Taylor P.C.,Colorado School of Mines | And 5 more authors.
Materials Research Society Symposium Proceedings | Year: 2010

We have used small-angle x-ray scattering (SAXS) in conjunction with X-ray diffraction (XRD) to study the nanostructure of hydrogenated nanocrystalline silicon (nc-Si:H). The crystallite size in the growth direction, as deduced from XRD data, is 24 nm with a preferred [220] orientation in the growth direction of the film. Fitting the SAXS intensity shows that the scattering derives from electron density fluctuations of both voids in the amorphous phase and H-rich clusters in the film, probably at the crystallite interfaces. The SAXS results indicate ellipsoidal shaped crystallites about 6 nm in size perpendicular to the growth direction. We annealed the samples, stepwise, and then measured the SAXS and ESR. At temperatures below 350°C, we observe an overall increase in the size of the scattering centers on annealing but only a small change in the spin density, which suggests that bond reconstruction on the crystallite surfaces takes place with high efficacy. © 2010 Materials Research Society. Source

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