Carrier transport mechanism in the SnO(2):F/p-type a-Si:H heterojunction

We characterize SnO(2):F/p-type a-Si:H/Mo structures by current-voltage (I-V) and capacitance-voltage (C-V) measurements at different temperatures to determine the transport mechanism in the SnO2:F/p-type a-Si:H heterojunction. The experimental I-V curves of these structures, almost symmetric around the origin, are ohmic for vertical bar V vertical bar< 0:1 V and have a super-linear behavior (power law) for vertical bar V vertical bar < 0:1 V. The structure can be modeled as two diodes back to back connected so that the main current transport mechanisms are due to the reverse current of the diodes. To explain the measured C-V curves, the capacitance of the heterostructure is modeled as the …

Reliability and Retention Study of Nanocrystal Cell Array

We have studied nanocrystal memory arrays with 2.56 × 105 cells (256kb) in which Si nanocrystals have been obtained by CVD deposition on a 4nm tunnel oxide. The cells in the array are programmed and erased by electron tunneling through the SiO2 dielectric. We find that the threshold voltage distribution has little spread. In addition the arrays are also very robust with respect to drain stress and show good retention.

Properties of SnO2:F/p-type aSi:H interface in thin film a-Si:H solar cells

Fabrication of Nanostructured Ni and Ni-Pd electrodes for wateralkaline electrolyzer

In the last years many attention has been dedicated to the increase of performance of Nichel based electrodes to use in water-alkaline electrolyzes. In our preliminary work we have shown that alkaline electrolyzer made with Ni nanowires covered with IrO2 (side oxygen evolution) nanoparticles and a Ni sheet (side hydrogen evolution) have very good and stable performance also at room temperature [1]. In this work, to obtain a complete nanostructured electrolyzer, the attention was focused on the fabrication of electrodes for hydrogen evolution. In particular, by metal displacement deposition we have grown on Ni nanowires electrodes, nanoparticles of Pd with the aim to enhance the electrocatal…

Radiation effects in nitride read-only memories

Abstract We report on the influence of different types of radiation on the nitride read-only memories (NROM®). The memory cells were irradiated by light ions (Boron), X-rays and γ-rays. Memory transistor parameters, such as threshold voltage and subthreshold drain leakage were studied as a function of the accumulated radiation dose and compared to the as-programmed (-erased) devices parameters. Their time evolution was registered in the range from few hours up to 5 months after the irradiation. The NROM® cells showed good radiation robustness up to high accumulated doses. Sufficient program margin (difference of threshold voltage in the programmed state and the read-out voltage level) remai…

Plasmonic modes in molybdenum ultra-thin films suitable for hydrogenated amorphous silicon thin film solar cells

We have recently demonstrated that molybdenum ultra-thin films interposed between hydrogenated amorphous silicon (a-Si:H) and SnO2:F transparent conductive oxide (TCO) in thin film solar cells show light trapping effects which enhance the solar cells performances. The effect of this improvement may be attributed to surface plasmon polariton (SPP) modes excited at the molybdenum interface by the solar radiation. In this paper we show direct evidence of such SPP modes in the case of the molybdenum/air interface by using the attenuated total reflection (ATR) technique, pioneered by Kretschmann, and we evaluate the dielectric constant of molybdenum at 660 nm. (C) 2013 The Authors. Published by …

Six patients with Pro250Arg mutation in FGFR3 in a family with coronal craniosynostosis: Intrafamilial variability and clinical management

Plasmonic effects of ultra-thin Mo films on hydrogenated amorphous Si photovoltaic cells

We report on the improvement of short circuit current (JSC), fill factor (FF), and open circuit resistance (ROC) in hydrogenated amorphous silicon (a-Si:H) photovoltaic cells with a p-type/intrinsic/n-type structure, achieved by the addition of an ultra-thin molybdenum film between the p-type film and the transparent conductive oxide/glass substrate. For suitable conditions, improvements of ≈10% in average internal quantum efficiency and up to 5%–10% under standard illumination in JSC, FF, and ROC are observed. These are attributed to the excitation of surface plasmon polariton modes of the a-Si:H/Mo interface.

Distribution of the threshold voltage window in nanocrystal memories with Si dots formed by chemical vapor deposition: Effect of partial self-ordering

Non volatile memories based on Si nanocrystals (Si-ncs) offer an important alternative to conventional floating gate devices, for the numerous potential advantages associated with the discrete-trap structures [1]. Isolated Si-ncs can be obtained by chemical vapor deposition (CVD) through a fully compatible CMOS process. So far, the main limitation for scaling the CVD Si-nc memories at sub-90 nm node is related to the expected fluctuation, from bit to bit, in the device threshold voltage (VTH), due to the spread in the sur- face fraction (Rdot) covered with Si dots [2]. The reason is the assumption that the dot position and the relative distance are fully random. It will be shown that the nu…

Effects of nitridation by N2O or NO on the electrical properties of thin gate or tunnel oxides

We have studied the effects of nitridation on the leakage current of thin (7-8 nm) gate or tunnel oxides. A polarity dependence of the tunneling current has been found this behavior is related to the presence of a thin silicon oxynitride layer at the SiO2/Si-substrate interface. The oxynitride layer lowers the tunneling current when electrons are injected from the interface where the oxynitride is located (substrate injection). The current flowing across the oxide when electrons are injected from the opposite interface (gate injection) is not influenced by the oxynitride. The increase of nitrogen concentration leads to a decrease of the tunneling current for substrate electron injection.

Fabrication and characterization of nanostructured Ni and Pd electrodes for hydrogen evolution reaction (HER) in water-alkaline electrolyzer

In the field of water-alkaline electrolyzer, the development of nanoporous low cost nickel electrodes is one of the potential approaches to increase electrocatalytic activity. Template electrodeposition is a facile and cheap technique for obtaining Ni nanowires (NWs) with high surface area. These nanostructures were fabricated by a two-step procedure. In the first step, a Ni compact layer was deposited on one side of the template where a gold film was previously sputtered, while, in the second-step, an ordered array of Ni-NWs was obtained by electrodeposition inside the template channels. The NWs were firmly connected to the underlying Ni layer, acting as a current collector. In order to en…

Impact of transparent conductive oxide on the admittance of thin film solar cells

Abstract The impact of transparent electrically conducting oxide (TCO) on the admittance measurements of thin film p–i–n a-Si:H solar cells was investigated. Admittance measurements on solar cell devices, with different area and geometry, in a wide range of frequencies and biases were performed. The admittance measurements of the investigated solar cells, which use the TCO as an electrical contact, showed that the high frequency admittance per area unit depends on the area. This effect increases both with the probe frequency and the size of the solar cells. Transmission line model valid for strip geometry which explains how the resistivity of the TCO layer impacts the measured admittance of…

Capacitance study of thin film SnO2:F/p-type a-Si:H heterojunctions

Abstract We characterized SnO 2 :F/p-type a-Si:H heterojunctions by current-voltage (I-V) and capacitance-voltage (C-V) measurements at room temperature to determine the junction parameters. Samples with circular geometry and different diameters were characterized. The current scales with the junction area, and the current density J as a function of the voltage V is a slightly asymmetric curve with a super-linear behaviour (cubic law) for high voltages. Using a transmission line model valid for devices with circular geometry, we studied the effects of the SnO 2 :F resistivity on the measured capacitance when the SnO2:F layer works as an electrical contact. The measured C-V curve allows us t…

Preliminary radiation hardness tests of single photon Si detectors

Single photon Si detectors were fabricated by STMicroelectronics and fully characterized in standard operation conditions and after irradiations. Both single cells and arrays, of dimensions ranging from 5x5 up to 64x64, were electrically tested. The devices operation was studied as a function of the temperature from -25 degrees C to 65 degrees C varying the voltage over breakdown, from 5% up to 20% of the breakdown voltage before and after irradiation using both light ions, 10 MeV B ions to doses in the range 3x10(7)-5x10(10) cm(-2), and X-rays irradiations in the range 0.5-20 krad(Si). Optical characterization was performed using a laser at 659 nm and opportunely chosen filters to vary the…

Fabrication of Nanostructured Ni and Ni-IrO2 electrodes for wateralkaline electrolyzer

In the field of water-alkaline electrolyzer, the develop of nanoporous nickel electrodes with low cost and high electrocatalysis efficiency is one of the potential approaches to increase their performance [1]. To obtain nanostructured electrodes, a facile approach is that of template electrosynthesis. With this method we have obtained electrodes made of nanowires of Ni that have a very high surface area. These electrode were obtained by a two-step procedure allowing to obtain an ordered array of Ni nanowires that completely covering the surface of current collector made of the same material. Besides, by amperostatic deposition we have covered these electrode with nanoparticles of IrO2 elect…

Memory cell structure integrated on semiconductor

This invention relates to a memory cell Which comprises a capacitor having a ?rst electrode and a second electrode separated by a dielectric layer. Such dielectric layer com prises a layer of a semi-insulating material Which is fully enveloped by an insulating material and in Which an electric charge is permanently present or trapped therein. Such electric charge accumulated close to the ?rst or to the second electrode, depending on the electric ?eld betWeen the electrodes,therebyde?ningdifferentlogiclevels.

Continuous Wave fNIRS with Silicon Photomultiplier

This work is focused on the development of a Continuous Wave (CW) NIRS integrated system with multi-wavelength LED sources between 700 and 950 nm and a Silicon Photomultiplier detector (SiPM) developed by STMicroelectronics. The Signal Noise Rate (SNR), measured placing the LEDs and an SiPM in a direct contact with the surface of a plastic phantom mimicking a real human head, results higher than the calculated minimum, required to detect small variation in the HbO2 and HHb concentration, till a source detector separation (SDS) of 6 cm.

Role of the Back Metal-Semiconductor Contact on the Performances of a-Si:H Solar Cells

We have investigated the role of the metal-semiconductor back contact on the performances of thin film modules consisting of single junction a-Si:H photovoltaic (PV) cells deposited with p-i-n configuration. We find that an adequate choice of the back contact helps reducing the barrier height of the junction improving the contact conductivity. For this purpose Mo has shown to be effective. Moreover we find that Mo, as refractory material, has additional beneficial effects reducing the formation of defects leading to the decrease of recombination losses. We have then fabricated a PV module on flexible substrate for indoor energy harvesting applications using Mo as back contact. An efficiency…

Experimental investigation and characterization of innovative bifacial silicon solar cells

The interest towards bifacial PV technology has increased over the last years, due to its potential capability of obtaining higher efficiencies with respect to traditional monofacial cells. Thus, the aim of this work is to present an experimental investigation on an innovative photovoltaic technology, such as the bifacial solar cells based on monocrystalline substrate. This analysis is mainly based on the determination of the current density/voltage, power density/voltage, External Quantum Efficiency (EQE) and Laser Beam Induced Current (LBIC) characterization. Interesting results are presented and discussed, demonstrating that the bifacial silicon solar cells can be a very promising techno…

Thin-film photovoltaics 2014 (Editorial)

Comparison between textured SnO2:F and Mo contacts with the p-type layer in p–i–n hydrogenate amorphous silicon solar cells by forward bias impedance analysis

Abstract In this paper we compare the performance of the textured SnO2:F and Mo contacts with the p-type layer in p–i–n hydrogenate amorphous silicon (a-Si:H) solar cells. We use standard current–voltage (I–V) electrical characterization methods coupled with forward bias small signal impedance analysis. We show the efficacy of this technique to determine the effective carrier lifetime in photovoltaic cells. We show that such effective lifetimes are indeed directly connected to the respective dark diode saturation currents. We also find that the effective lifetime is constant with the temperature in the 0–70 °C range and it is significantly better for the solar cell with Mo diode contact. Th…