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Series Resistance (series + resistance)
Kinds of Series Resistance Selected AbstractsEfficiency Enhancement in Organic Photovoltaic Cells: Consequences of Optimizing Series ResistanceADVANCED FUNCTIONAL MATERIALS, Issue 1 2010Jonathan D. Servaites Abstract Here, means to enhance power conversion efficiency (PCE or ,) in bulk-heterojunction (BHJ) organic photovoltaic (OPV) cells by optimizing the series resistance (Rs),also known as the cell internal resistance,are studied. It is shown that current state-of-the-art BHJ OPVs are approaching the limit for which efficiency can be improved via Rs reduction alone. This evaluation addresses OPVs based on a poly(3-hexylthiophene):6,6-phenyl C61 -butyric acid methyl ester (P3HT:PCBM) active layer, as well as future high-efficiency OPVs (,,>,10%). A diode-based modeling approach is used to assess changes in Rs. Given that typical published P3HT:PCBM test cells have relatively small areas (,0.1,cm2), the analysis is extended to consider efficiency losses for larger area cells and shows that the transparent anode conductivity is then the dominant materials parameter affecting Rs efficiency losses. A model is developed that uses cell sizes and anode conductivities to predict current,voltage response as a function of resistive losses. The results show that the losses due to Rs remain minimal until relatively large cell areas (>0.1,cm2) are employed. Finally, Rs effects on a projected high-efficiency OPV scenario are assessed, based on the goal of cell efficiencies >10%. Here, Rs optimization effects remain modest; however, there are now more pronounced losses due to cell size, and it is shown how these losses can be mitigated by using higher conductivity anodes. [source] Electrode Grids for ITO Free Organic Photovoltaic Devices,ADVANCED MATERIALS, Issue 19 2007K. Tvingstedt Silver grids are utilized to exclude the expensive use of indium tin oxide (ITO) in conjugated polymer photovoltaic devices. The grids are generated by electroless deposition from elastomeric microfluidic channels onto transparent substrates. The organic photovoltaic devices demonstrated here, with minimized series resistance, are confirmed to have characteristics comparable to devices exploiting ITO. [source] Electrical characteristics of Al/polyindole Schottky barrier diodes.JOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2009Abstract In this study, the forward and reverse bias current,voltage (I,V), capacitance,voltage (C,V), and conductance,voltage (G/,,V) characteristics of Al/polyindole (Al/PIN) Schottky barrier diodes (SBDs) were studied over a wide temperature range of 140,400 K. Zero-bias barrier height ,B0(I,V), ideality factor (n), ac electrical conductivity (,ac), and activation energy (Ea), determined by using thermionic emission (TE) theory, were shown fairly large temperature dispersion especially at lower temperatures due to surface states and series resistance of Al/PIN SBD. I,V characteristics of the Al/PIN SBDs showed an almost rectification behavior, but the reverse bias saturation current (I0) and n were observed to be high. This high value of n has been attributed to the particular distribution of barrier heights due to barrier height inhomogeneities and interface states that present at the Al/PIN interface. The conductivity data obtained from G/,V measurements over a wide temperature range were fitted to the Arrhenius and Mott equations and observed linear behaviors for ,ac vs. 1/T and ln ,ac vs. 1/T1/4 graphs, respectively. The Mott parameters of T0 and K0 values were determined from the slope and intercept of the straight line as 3.8 × 107 and 1.08 × 107 Scm,1K1/2, respectively. Assuming a value of 6 × 1012 s,1 for ,0, the decay length ,,1 and the density states at the Fermi energy level, N(EF) are estimated to be 8.74 Å and 1.27 × 1020 eV,1cm,3, respectively. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Distributed inductance and resistance per-unit-length formulas for VLSI interconnects on silicon substrateMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 5 2001H. Ymeri Abstract A new analytic model is presented (the model is based on the induced current density distribution inside silicon substrate) to calculate the frequency-dependent distributed inductance and the associated distributed series resistance of silicon semiconducting VLSI interconnects. The validity of the proposed model has been checked by a comparison with CAD-oriented modeling methodology in conjunction with a quasi-TEM spectral-domain approach. It is found that the silicon semiconducting substrate skin effect must be considered for the accurate prediction of the high-frequency characteristics of VLSI interconnects. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 30: 302,304, 2001. [source] Fast series resistance imaging for silicon solar cells using electroluminescencePHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 7-8 2009Jonas Haunschild Abstract We introduce a fast and easy to apply method for determining the local series resistance of standard silicon solar cells. For this method only two electroluminescence images taken at different voltages are needed. From these two images, the local voltage and the local current density through the device can be calculated. Knowing these parameters for each pixel yields the local series resistance. By calculating the cell's dark saturation current from the lower voltage image, the method also works with multicrystalline material. We show images, acquired in only 300 ms and compare them with other luminescence based series resistance images. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Influence of top layer geometries on the electronic properties of pentacene and diindenoperylene thin filmsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 3 2008M. Scharnberg Abstract Top layers have a pronounced influence on the electronic properties of molecular organic thin films. Here, we report about the changes induced by metallic and polymeric top layers and contacts. As test structures, model systems of diindenoperylene and pentacene crystalline molecular organic thin films are used. A very sensitive radiotracer technique is introduced to study the details of metal penetration during top contact formation. The influence of temperature, evaporation time, adhesion promoter and grain size of the organic film were examined. The electric currents passing through metal top contacts were found to vary by more than a factor of three, depending on the preparation conditions of the metal contact. Furthermore, the series resistance of chemically identical contacts that only differed in the morphology of the interface were found to show pronounced asymmetric conductivity behaviour. We also show that with the help of electret top layers, based on the Teflon-AF fluropolymer, the threshold voltage of an organic field effect transistor can be tuned by several volts. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Transparent ohmic contacts to GaSb/In(Al)GaAsSb photovoltaic cellsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 4 2007K. Golaszewska Abstract In this paper we present the results of study of thin oxide films: CdO, ZnO and RuSiO4 used as transparent ohmic contacts to GaSb/InGaAsSb/AlGaAsSb photodiodes. Thin oxide films with thickness of 50 nm were deposited by magnetron sputtering. CdO and RuSiO4 were formed in a reactive process in Ar,O2 atmosphere, from Cd and Ru1Si1 targets, respectively. ZnO films were deposited directly from ZnO target by rf sputtering. We have shown that application of CdO, ZnO and RuSiO4 transparent films instead of conventional metal-based contacts enables to improve of photodiode properties. As a result, GaSb/InGaAsSb/AlGaAsSb photodiodes with detectivity D * increased by factor of 2 and reduced by factor of 3 the series resistance were obtained. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Modeling of spatially inhomogeneous solar cells by a multi-diode approachPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 15 2005P. O. Grabitz Abstract An equivalent circuit model consisting of parallel connected diodes with different electronic quality simulates the electronic properties of solar cells with spatially inhomogeneous material quality. Variations of the local saturation current density result in a degradation of the open circuit voltage, the fill factor and, in consequence, of the overall power conversion efficiency. However, a local series resistance introduced into this network limits this degradation by preventing areas with high saturation current density to dominate the electronic losses of the entire device. Analyzing the integral current/voltage-curves of the networks shows the diode ideality larger than unity to result from resistive limitations to the spatially inhomogeneous current flow. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Characteristics of He+ -irradiated Ni Schottky diodes based on 4H-SiC epilayer grown by sublimationPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2009A. M. Strel'chuk Abstract Forward and reverse current-voltage (I-V) and capacitance-voltage (C-V) characteristics of the of He+ , irradiated Ni-SiC(4H) Schottky diodes (SDs) are presented prior and after irradiation. The effect of irradiation was weakly observed in the region of small forward and reverse current, but series resistance of SD demonstrated tendency to rise with increasing irradiation dose. The most interesting effect was the big scatter of the series resistances after exposure to high irradiation dose 2×1012 cm -2. By contrast, uncompensated donor concentration had just minor changes (from 3.3×1017 cm -3 prior irradiation to 1.8×1017 cm -3 at highest irradiation dose) with no connection with SDs resistance. Hypothesis that localized defect-induced current paths could explain this behaviour is discussed. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The effect of absorption layer of different quantum well arrangement on optoelectronic characteristics of nitride-based photovoltaic cells grown by MOCVDPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009Y. K. Fu Abstract In this study, III-nitride solar cells with multi-quantum well (MQW) absorption layer were grown on sapphire substrates by metal organic chemical vapor deposition (MOCVD). The effect of different quantum well (QW) arrangement on optoelectronic characteristics of III-nitrides photovoltaic cells was investigated. It was found that the upper quantum well (QW) layer will dominate electroluminescence (EL) emission mechanism and the electrical characteristics of solar cell. The advantage of modulating the short-circuit current density (JSC) and open-circuit voltage (VOC) can be obtained by different arrangement of blue and green QW in MQW absorption layer. The optimum electrical characteristics of solar cell with a JSC of 0.30 mA/cm2, a VOC up to 1.51 V, fill factor (FF) as high as 0.601, and a series resistance (RS) of 9 , can be obtained by using MQW absorption layer. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Study of the influence of ,-particles irradiation on AlGaAs/GaAs heterojunction structuresPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2008P. Georgakakos Abstract Aim of the present work is to study the influence of the radiation of ,-particles (5 MeV) in Schottky diodes on CaAs/AlGaAs/GaAs heterojunction structures. The investigation was performed by means of current-voltage and capacitance-voltage characteristics in 300 K temperature. The dependence of ideality factor, barrier height, carrier concentration and series resistance as a function of radiation fluence was determined. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Current spreading and thermal effects in blue LED dicePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2007K. A. Bulashevich Abstract We have applied simulations to study current the spreading and heat transfer in blue III-nitride light-emitting diodes (LEDs) with the focus on self-heating and its effect on the device characteristics. A conventional planar design of an LED die is considered for the heat sink through a sapphire substrate. The computations predict a great current crowding at the contact electrode edges, resulting in a non-uniform temperature distribution over the die. The thermal effect on the current-voltage characteristic, output optical power, and series resistance of the diode is analyzed and the theoretical predictions are compared with available observations. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Current crowding effects on blue LED operationPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2006I. Yu. Abstract A hybrid 1D/3D approach to modeling of the electric current spreading in a light emitting diode (LED) die is suggested and validated by comparing the theoretical predictions with available observations. Large-area LEDs with different contact electrode configurations suitable for high-power operation are analyzed in terms of simulations with the focus on the current non-uniformity and its impact on the device electrical and optical characteristics. The factors controlling the LED series resistance are identified by modeling, and ways for the resistance improvement are examined. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Study of base series resistance losses in single and double emitter silicon solar cells through simulations and experimentsPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 7 2008K. Kotsovos Abstract This work focuses on base series resistance influence on the performance of single and double emitter rear point contact silicon solar cells. This study is performed through measurements on experimental devices with different rear contact sizes and spacings, which were designed and fabricated using standard silicon integrated circuit technology, while the results were compared with simulation data based on a 3D model developed at our institute. Simulation and experimental results show that the series resistance of the double junction structure is significantly lower compared to the single junction equivalent. In addition, it was demonstrated that the operation of both junctions under slightly different voltages improves device efficiency. Copyright © 2008 John Wiley & Sons, Ltd. [source] GaAs converters for high power densities of laser illuminationPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 4 2008E. Oliva Abstract Photovoltaic power converters can be used to generate electricity directly from laser light. In this paper we report the development of GaAs PV power converters with improved conversion efficiency at high power densities. The incorporation of a lateral conduction layer (LCL) on top of the window layer resulted in a considerable gain in efficiency at high illumination levels. Additional performance improvements were obtained by using a metal electrode grid design and antireflection coating optimised for monochromatic and inhomogeneous laser light. Maximum monochromatic (810,nm) optical-to-electrical conversion efficiency of 54·9% at 36·5,W/cm2 has been achieved. The characteristics of laser power converters with p/n and n/p polarity are discussed in this paper. Moreover, different materials and doping levels were applied in the LCL. The performance of these different device structures at high laser intensity is presented and discussed. It is shown that the lateral series resistance of the cell has a major impact on the overall device performance. Copyright © 2008 John Wiley & Sons, Ltd. [source] Series resistance characterization of industrial silicon solar cells with screen-printed contacts using hotmelt pastePROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 6 2007A. Mette Abstract This work presents the results of a detailed series resistance characterization of silicon solar cells with screen-printed front contacts using hotmelt silver paste. Applying the hotmelt technology energy conversion efficiencies up to 18·0% on monocrystalline wafers with a size of 12·5,cm,×,12·5,cm have been achieved, an increase of 0·3% absolute compared to cells with conventional screen-printed contacts. This is mainly due to the reduction in the finger resistance to values as low as 14,,/m, which reduces the series resistance of the solar cell significantly. To retrieve the lumped series resistance as accurately as possible under the operating condition, different determination methods have been analyzed. Methods under consideration were fitting of the two-diode equation function to a dark IV-curve, integration of the area A under an IV-curve, comparison of a jsc,Voc with a one-sun IV-curve, comparison of the jsc and Voc points of a shaded curve with the one-sun IV-curve as well as comparison of a dark IV-curve with a one-sun IV-curve, and comparison of IV-curves measured at different light intensities. The performed investigations have shown that the latter four methods all resulted in reliable series resistance values. Copyright © 2007 John Wiley & Sons, Ltd. [source] Effective efficiency of PV modules under field conditionsPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 1 2007Marko Topi Abstract The conversion efficiency of photovoltaic modules varies with irradiance and temperature in a predictable fashion, and hence the effective efficiency averaged over a year under field conditions can be reliably assessed. The suggested procedure is to define the efficiency versus irradiance and temperature for a specific module, collect the local irradiance and temperature data, and combine the two mathematically, resulting in effective efficiency. Reasonable approximations simplify the process. The module performance ratio is defined to be the ratio of effective efficiency to that under standard test conditions. Variations of the order of 10% in this factor among manufacturers, primarily the result of the differences in effective series resistance and leakage conductance, are not unusual. A focus on these parameters that control the effective efficiency should provide a path to PV modules with improved field performance. Copyright © 2006 John Wiley & Sons, Ltd. [source] Explanation of high solar cell diode factors by nonuniform contact resistancePROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 1 2005A. S. H. van der Heide Abstract The current density,voltage (J,V) curve that characterises the performance of a solar cell is often extra rounded, resulting in reduced efficiency. When fitting to the standard one-dimensional models, it is often found that the rounding cannot be fitted by the series resistance only. In these cases, the diode factor m or the depletion region saturation current density J0DR (depending on the model used) is increased. This behaviour could not be explained so far; this paper discusses if a nonuniform contact resistance of the front side metallisation leads to an increase of m or J0DR. The theoretical part of the investigation is the simulation of the curve for a cell with two regions with different contact resistance. It was found indeed that m or J0DR is increased, while the series resistance is not increased as much as expected. The experimental part was the calculation of the J,V curve of a high- m solar cell with local contact resistances measured with the so-called Corescan and the cell's resistanceless J,V curve as measured with the so-called Suns- Voc method. The calculated curve approximated the actual curve quite well, demonstrating in practice that high diode factors can be explained by nonuniform contact resistance. Copyright © 2004 John Wiley & Sons, Ltd. [source] Spatially resolved evaluation of power losses in industrial solar cells by illuminated lock-in thermographyPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 5 2004Joerg Isenberg Abstract The principles of a recently introduced measurement technique for power losses in solar cells, illuminated lock-in thermography (ILT), are reviewed. The main advantage of ILT over dark lock-in Thermography (DLT) is measurement under realistic operational conditions of solar cells. The main focus of this paper is to demonstrate the wide range of applications of ILT in identifying the causes of power losses in solar cells. For this purpose different evaluation methods are presented. A method for the evaluation of improvement potentials within a given cell technology is demonstrated. It is shown that different types of series resistance may be localized. Small areas of recombination losses (e.g., grain boundaries) can routinely be detected, which is not possible in dark lock-in thermography. Good correspondence with light-beam-induced current images is found. A realistic evaluation of the impact of recombination losses on solar cell performance is demonstrated on two examples. Finally, process- or treatment-induced recombination losses are investigated. In summary ILT is shown to be an extremely powerful tool in localizing, identifying and quantifying power losses of solar cells under realistic illumination conditions. Copyright © 2004 John Wiley & Sons, Ltd. [source] Local series resistance mapping of silicon solar cells by microwave photoconductivity decay measurementsPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 5 2003C. Ballif We present a new non-destructive mapping technique which yields information on the local series resistance in Si solar cells. The technique is based on microwave photoconductivity decay measurements performed on reverse-biased Si solar cells. For reverse-biased devices, the initial decay time measured after a high-intensity laser pulse is shown to be directly proportional to the local series resistances between the excited area and the cell metallisation. We illustrate how high contact resistance between the fingers and the emitter, resistive back-surface contacts or finger interruptions lead to an increase of the microwave detected decay time. Copyright © 2003 John Wiley & Sons, Ltd. [source] Performance prediction of concentrator solar cells and modules from dark I,V characteristicsPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 3 2003I. Antón The indoor performance of concentrator solar cells and modules at operating conditions is a complex task, owing to the required illumination and temperature conditions, and even more so during extensive procedures, such as on a production line. The solution proposed throughout this paper consists of predicting the illumination I,V characteristic of the solar cells, with the dark I,V curve and the photogenerated current as the only input data. As well as this, the technology-dependent components of the series resistance are obtained from the dark characteristics for quality control. Theory and experiments on several types of concentrator cell have been carried out to validate the method. The equipment to be used on a production line has been developed by IES and used by BP Solar to test up to 25 000 cells and 2000 modules for the 480,kWp power plant using the EUCLIDESTM concentrator. Copyright © 2003 John Wiley & Sons, Ltd. [source] Manufacturing tolerances of terrestrial concentrator p-on-n GaAs solar cellsPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 1 2001Carlos Algora The increasing interest in the manufacturing of terrestrial concentrator GaAs solar cells calls for the need to establish the guidelines, assessments and tolerances of the production process. Accordingly, this paper analyses, for the first time, the tolerances of this process. The influence of the entire solar cell (antireflecting coatings, semiconductor structure and series resistance) is considered. More specifically, the parameters analysed are: the thickness of the double antireflecting coating, window thickness, emitter thickness, base thickness, emitter doping level, base doping level, shadowing factor and specific front contact resistance. The results are presented in the form of iso-efficiency plots as a function of the aforementioned parameters. Therefore, besides the conclusions extracted in this paper, numerous others may be formed according to particular necessities. Copyright © 2001 John Wiley & Sons, Ltd. [source] CFTR fails to inhibit the epithelial sodium channel ENaC expressed in Xenopus laevis oocytesTHE JOURNAL OF PHYSIOLOGY, Issue 3 2005G. Nagel The cystic fibrosis transmembrane conductance regulator (CFTR) plays a crucial role in regulating fluid secretion by the airways, intestines, sweat glands and other epithelial tissues. It is well established that the CFTR is a cAMP-activated, nucleotide-dependent anion channel, but additional functions are often attributed to it, including regulation of the epithelial sodium channel (ENaC). The absence of CFTR-dependent ENaC inhibition and the resulting sodium hyperabsorption were postulated to be a major electrolyte transport abnormality in cystic fibrosis (CF)-affected epithelia. Several ex vivo studies, including those that used the Xenopus oocyte expression system, have reported ENaC inhibition by activated CFTR, but contradictory results have also been obtained. Because CFTR,ENaC interactions have important implications in the pathogenesis of CF, the present investigation was undertaken by our three independent laboratories to resolve whether CFTR regulates ENaC in oocytes and to clarify potential sources of previously reported dissimilar observations. Using different experimental protocols and a wide range of channel expression levels, we found no evidence that activated CFTR regulates ENaC when oocyte membrane potential was carefully clamped. We determined that an apparent CFTR-dependent ENaC inhibition could be observed when resistance in series with the oocyte membrane was not low enough or the feedback voltage gain was not high enough. We suggest that the inhibitory effect of CFTR on ENaC reported in some earlier oocyte studies could be attributed to problems arising from high levels of channel expression and suboptimal recording conditions, that is, large series resistance and/or insufficient feedback voltage gain. [source] A novel silicon patch-clamp chip permits high-fidelity recording of ion channel activity from functionally defined neuronsBIOTECHNOLOGY & BIOENGINEERING, Issue 4 2010Christophe Py Abstract We report on a simple and high-yield manufacturing process for silicon planar patch-clamp chips, which allow low capacitance and series resistance from individually identified cultured neurons. Apertures are etched in a high-quality silicon nitride film on a silicon wafer; wells are opened on the backside of the wafer by wet etching and passivated by a thick deposited silicon dioxide film to reduce the capacitance of the chip and to facilitate the formation of a high-impedance cell to aperture seal. The chip surface is suitable for culture of neurons over a small orifice in the substrate with minimal leak current. Collectively, these features enable high-fidelity electrophysiological recording of transmembrane currents resulting from ion channel activity in cultured neurons. Using cultured Lymnaea neurons we demonstrate whole-cell current recordings obtained from a voltage-clamp stimulation protocol, and in current-clamp mode we report action potentials stimulated by membrane depolarization steps. Despite the relatively large size of these neurons, good temporal and spatial control of cell membrane voltage was evident. To our knowledge this is the first report of recording of ion channel activity and action potentials from neurons cultured directly on a planar patch-clamp chip. This interrogation platform has enormous potential as a novel tool to readily provide high-information content during pharmaceutical assays to investigate in vitro models of disease, as well as neuronal physiology and synaptic plasticity. Biotechnol. Bioeng. 2010;107:593,600. © 2010 Wiley Periodicals, Inc. [source] Long-wavelength (, , 1.3 µm) InGaAlAs,InP vertical-cavity surface-emitting lasers for applications in optical communication and sensingPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 14 2006Markus-Christian Amann Abstract In this paper we present an overview of the properties and applications of long-wavelength vertical-cavity surface-emitting lasers (VCSELs) based on the InGaAlAs,InP material system. With respect to significant temperature sensitivity of active material gain as well as insufficient thermal conductivity of InP-based epitaxial compound layers, the effective thermal heat management appears as a major issue for application suitable device performance. In this context, the incorporation of a buried tunnel junction (BTJ) in connection with improved heat sinking resembles a breakthrough for long-wavelength VCSELs. With the utilization of n-type spreading layers and consequently ultralow series resistances, BTJ-VCSELs exhibit sharply reduced excess heat generation. Furthermore, the BTJ-approach enables self-aligned optical and current confinement. A hybrid dielectric stack with Au-coating yields an improved thermal heatsinking. The current status of BTJ-VCSELs encompasses a number of superior performance values. At 1.55 µm wavelength, this includes room temperature single- and multimode continuous wave (cw) output powers of more than 3 mW and 10 mW, respectively, laser operation for heat sink temperatures well exceeding 100 °C, and optical data transmission rates up to 10 Gbit/s. The versatility of compound layer composition enables arbitrary emission wavelengths within a broad range of 1.3 and 2 µm. With respect to sensing applications, BTJ-VCSELs appear as ideal components for optical detection of infrared active gases. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Characteristics of He+ -irradiated Ni Schottky diodes based on 4H-SiC epilayer grown by sublimationPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2009A. M. Strel'chuk Abstract Forward and reverse current-voltage (I-V) and capacitance-voltage (C-V) characteristics of the of He+ , irradiated Ni-SiC(4H) Schottky diodes (SDs) are presented prior and after irradiation. The effect of irradiation was weakly observed in the region of small forward and reverse current, but series resistance of SD demonstrated tendency to rise with increasing irradiation dose. The most interesting effect was the big scatter of the series resistances after exposure to high irradiation dose 2×1012 cm -2. By contrast, uncompensated donor concentration had just minor changes (from 3.3×1017 cm -3 prior irradiation to 1.8×1017 cm -3 at highest irradiation dose) with no connection with SDs resistance. Hypothesis that localized defect-induced current paths could explain this behaviour is discussed. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Luminescence imaging for the detection of shunts on silicon solar cellsPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 4 2008M. Kasemann Abstract Luminescence imaging is a non-destructive, fast, and versatile imaging method for spatially resolved solar cell and material characterization. In this paper, we investigate its ability to detect shunts on silicon solar cells. We give a detailed description of the relation between local junction voltage and local luminescence signal. This relation is important because shunts drain majority currents causing voltage drops across the surrounding series resistances and that way affect luminescence images. To investigate effects related to majority currents, we describe and apply a simulation model that allows the simulation of lateral voltage distributions on solar cells. This model, and a comparison to illuminated lock-in thermography, helps to discuss some practical aspects about shunt detection by luminescence imaging. We will discuss a procedure to distinguish between ohmic and diode-like shunts and finally present simulations and measurements showing that luminescence imaging is only weakly sensitive to shunts under the metallization. However, we also show its high sensitivity for remote shunts and propose a possible application where this high sensitivity could be especially helpful. Copyright © 2008 John Wiley & Sons, Ltd. [source] Local series resistance mapping of silicon solar cells by microwave photoconductivity decay measurementsPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 5 2003C. Ballif We present a new non-destructive mapping technique which yields information on the local series resistance in Si solar cells. The technique is based on microwave photoconductivity decay measurements performed on reverse-biased Si solar cells. For reverse-biased devices, the initial decay time measured after a high-intensity laser pulse is shown to be directly proportional to the local series resistances between the excited area and the cell metallisation. We illustrate how high contact resistance between the fingers and the emitter, resistive back-surface contacts or finger interruptions lead to an increase of the microwave detected decay time. Copyright © 2003 John Wiley & Sons, Ltd. [source] | |||||||||||||||||||