Interface states and traps in thin N2O-grown oxynitride/oxide di-layer for PowerMOSFET devices

A detailed study of the interface state properties shown by the silicon/oxynitride/oxide gate layers used in Vertically Diffused PowerMOSFET (PowerVDMOS) technologies is reported. A quantitative analysis of interface states versus the specific N₂O based nitridation process, extracted from current–voltage characteristics in depletion regime, provided a clear trend and turns to be of great importance for reliability performances of the final device.     

Mass Balance in Eulerian-Lagrangian Transport Simulations in Estuaries

This paper investigates the generation of flow mass errors in finite-element shallow water models and the effect of these errors in the mass conservation of Eulerian-Lagrangian transport simulations. Flow mass errors are shown to be similar for several primitive and wave equation formulations. These errors occur primarily in areas of steep bathymetric gradients and near complex boundaries. Forcing Eulerian-Lagrangian transport simulations with nonconservative flow fields generates important mass imbalances, which can be mitigated by refining the flow grid. Comparatively, refining the transport grid only reduces marginally the mass errors.     

Diverticula of the female urethra

OBJECTIVES: The contribution of ultrasonography to pretreatment morphological assessment of strictures of the anterior urethra and assessment of the risk of recurrence after internal urethrotomy. MATERIAL AND METHODS: 33 patients (16-89 years) operated by internal urethrotomy for stricture of the anterior urethra and followed for at least 6 months. Preoperative urethral ultrasonography, recording the number, length and degree of strictures and echostructure of the peristenotic fibrosis of the corpus spongiosium. RESULTS: Ultrasound visualization of all urethral strictures, with no false-positives and no false-negatives. 11 patients relapsed after a mean interval of 5.7 months (1-16 months), 22 patients did not present recurrence: mean interval: 15.5 months (6-36 months). Corpus spongiosum fibrosis associated with urethral stricture is isoechoic to the corpus spongiosum (19 cases) or hyperechoic to the corpus spongiosum (14 cases). No statistical correlation was observed between the echostructure of the fibrous tissue and the risk of recurrence after internal urethrotomy. CONCLUSION: Ultrasonography allows excellent analysis of the morphological characteristics of a stricture of the male anterior urethra. In our experience, and in contrast with the limited data of the literature, no correlation was observed between the echostructure of the peristenotic fibrosis and the risk of recurrence after internal urethrotomy.     

Influence of the layer thickness and hydrogen dilution on electrical properties of large area amorphous silicon p–i–n solar cell

The aim of this work is to present data concerning the optimization of performances of a large area amorphous silicon p–i–n solar cell (30×40 cm²) deposited by plasma enhanced chemical vapour deposition (PECVD) at 27.12 MHz. In this work the solar cell was split into small areas of 0.126 cm², aiming to study the device performance uniformity, where emphasis was put on the role of the n-layer thickness. The solar cells were studied through the spectral response behaviour in the 400–750 nm range as well as by the behaviour of the AC impedance. Solar cells with fill factor of 0.58, open circuit voltage of 0.83 V, short circuit current density of 17.14 mA/cm² and an efficiency of 8% were obtained at growth rates higher than 0.3 nm/s.     

Silicon thin films prepared in the transition region and their use in solar cells

Diphasic silicon films (nc-Si/a-Si:H) have been prepared by a new regime of plasma enhanced chemical vapour deposition in the region adjacent of phase transition from amorphous to microcrystalline state. Comparing to the conventional amorphous silicon (a-Si:H), the nc-Si/a-Si:H has higher photoconductivity (σ_ph), better stability, and a broader light spectral response range in the longer wavelength range. It can be found from Raman spectra that there is a notable improvement in the medium range order. The blue shift for the stretching mode and red shift for the wagging mode in the IR spectra also show the variation of the microstructure. By using this kind of film as intrinsic layer, a p–i–n junction solar cell was prepared with the initial efficiency of 8.51% and a stabilized efficiency of 8.01% (AM1.5, 100 mw/cm²) at room temperature.     

Carrier trapping in thin N2O-grown oxynitride/oxide di-layer for PowerMOSFET devices

A detailed study of the carrier trapping properties shown by the silicon/oxynitride/oxide gate layers in PowerVDMOS technologies is reported. A quantitative analysis of hole and electron trap densities versus the specific N₂O based nitridation process, extracted from Fowler–Nordheim constant current stress kinetics, allows a deep understanding of the role played by those defects in the susceptibility of every nitrided layer.     

Conductivity and noise in thin films of nonhydrogenated amorphous silicon in the hopping regime

Excess noise measurements have been carried out in nonhydrogenated amorphous silicon material at room temperature. The temperature dependence of the conductivity has shown that, at room temperature, noise measurements deal with transport mechanisms dominated by hopping to nearest neighbors. At lower temperature there is variable range hopping from which the number of states near the Fermi level was determined. The ohmic behavior of structures such as molybdenum-amorphous silicon-molybdenum, and the V² dependence of the noise spectral density indicate that $\text{1}\text{f}$ noise is characteristic for this material. A simple theory of phonon assisted hopping $\text{1}\text{f}$ noise is presented. From this the fluctuations. Some preliminary data are shown for hydrogenated amorphous silicon. The noise shows a Lorentzian, indicative of generation-recombination noise.     

Analysis of spontaneous and double-strand break-induced recombination in rad mutants of S. pombe

Schizosaccharomyces pombe strains containing direct repeats of adeó heteroalleles separated by a functional uro4+ gene, and a DNA site for induction of a double-strand break (DSB), have been used to analyze pathways of spontaneous and DSB-induced intrachromosomal mitotic recombination. These substrates yield Ade+ Ura+ convertants or Ade+ Ura- deletions, by the DSB/gap repair and single-strand annealing (SSA) pathways of recombination, respectively. In S. cerevisiae, the DSB/gap repair pathway is RAD52 dependent, and the RAD1 and RAD10 genes are involved in the SSA pathway. We have sought to understand the genetic control of the pathways of mitotic recombination in S. pombe by determining the effects of mutations in six rad genes involved in DNA repair: rad1 and rad3 involved in checkpoint control in response to unreplicated or damaged DNA; rad5 (homologue of S. cerevisiae RAD3) and rad10 (homologue of S. cerevisiae RAD1) involved in nucleotide excision repair; rad21 and rad22 (homologue of S. cerevisiae RAD52) involved in the repair of ionizing radiation-induced DNA damage. The results suggest that the genetic control of the pathways of spontaneous and DSB-induced mitotic intrachromosomal recombination in S. pombe is different from that in S. cerevisiae.     

Anomalous off-current mechanisms in N-channel poly-Si thin film transistors

The anomalous off-current (I_off) in polysilicon thin film transistors (polysilicon TFTs) is one of the major problems preventing a wide use of these devices in active matrix liquid crystal displays. While previous investigations have focused on the temperature range above 300 K, in this study we have investigated the behaviour of I_off over a wide range of temperatures, namely 180–400 K. The data have been analysed by combining 2D simulations and existing analytic models. By this approach we have identified a pure trap-to-band tunnelling mechanism in polysilicon TFTs and deduced, by a simple procedure, the physical constants. The temperature and bias dependence of the off-current has been explained quantitatively in terms of phonon-assisted tunnelling. The number of generating centres, the dominant trap energy and the thermal capture cross section are deduced from this analysis.