An approach to the measurement of shunt resistance of individual subcells in thin‐film tandem devices

In this paper, the selective illumination approach is adopted to separately extract the shunt resistance of the individual subcells belonging to a tandem cell. The method relies on simple theoretical considerations and is based on the measurement of the current–voltage characteristic of the tandem cell by alternately keeping one of the subcells under dark conditions. Numerical simulations are employed to support the reliability of the technique, which is experimentally tested on micromorph devices deposited onto glass covered by a V‐shaped transparent conducting oxide and subject to different thermal treatments. Copyright © 2013 John Wiley & Sons, Ltd.     

An improved test structure for recombination lifetime profilemeasurements in very thick silicon wafers

A new test structure for recombination lifetime profile measurements has been designed and applied, for the first time, to the characterization of very thick bulk silicon wafers. The capability of the new test device to reject parasitic effects, affecting the reliability of the measure in bulk wafers, is shown by means of two-dimensional (2-D) simulations and experimental results. The proposed device has permitted the characterization of two P-type silicon bulk samples. For the first time a clear experimental evidence that the dopant acts as a recombination center has been found in this kind of material     

Spectroscopic measurements of non-equilibrium nitrogen plasmas at moderate pressures

A local vibro-rotational analysis of the excited species, produced in a 35 MHz discharge reactor in flowing nitrogen, has been carried out by measuring radial and axial emission intensities of some vibrational sequences and selected rotational lines of the (0,2) band of the second positive system (SPS) of N₂ (C³Π_u - B³Π_g), in the pressure range 5–35 torr.Radial from lateral band or line emission intensities have been obtained by applying Abel's inversion technique to derive the corresponding vibrational and rotational temperatures with the use of Boltzmann plots. General maps of emission intensities and of vibrational and rotational temperature distributions within the reactor have been drawn.It is shown that a decrease of a factor 10³ in the emission intensities from the core to the periphery of the discharge corresponds to a variation in T_V and T_R of only a factor ?2. This result has been interpreted on the basis of the kinetic mechanisms for the excitation and deexcitation of chemical species under discharge conditions. The decrease of _V and the increase of T_R with increasing pressure are interpreted according to V-R (vibration-rotation) energy-transfer mechanisms.     

Influence of hydrogenated oligo(cyclopentadiene) on the structure and the thermal degradation of polypropylene-based nanocomposites

Polypropylene has been compounded with a commercial organoclay both in the absence and in the presence of hydrogenated oligo(cyclopentadiene) (HOCP) as a compatibiliser. The characteristics and the properties of the nanocomposites were evaluated and compared. HOCP favours the intercalation of the polypropylene in the organoclay galleries and enables a more homogeneous dispersion of the nanoclay throughout the polymer matrix. In the compatibilised nanocomposite, the diluent effect ascribed to the HOCP component is associated with the nucleating action of the nanoclay, resulting in the development of the β-crystalline form of the polypropylene. The presence of HOCP preserves the molecular weight of the polymer during the processing and gives good overall mechanical properties to the compatibilised nanocomposite. The thermo-oxidative degradation of the polypropylene is strongly delayed in the compatibilised nanocomposite.     

Two-dimensional analysis of a test structure for lifetime profilemeasurements

A new electrical measurement technique has been proposed that allows one to obtain the “local” lifetime value in Si layers, by superposing ac measurements on a dc bias in a three-terminal test structure, and hence to extract a lifetime “profile” along the depth of the layer by varying the voltage bias. In this paper two-dimensional effects that could arise due to the lateral current flow in the test structure are studied, and are related to the modifications of the lifetime profile extracted. Both a simplified analysis and 2-D simulations of the test structure behavior allow one to explain the 2-D effects responsible for deviation of the lifetime profile from the correct one as dependent on the geometry of the test structure. Moreover design rules are given for the test structure, that keep the error in the profile extracted within safe limits     

Chemical mechanisms in C3F8-H2 radiofrequency discharges

Discharges fed with C₃F₈-H₂ mixtures have been studied by means of mass spectrometry in a tubular reactor operated at 0.5 torr and 50 W. Comparison of the results with those obtained with emission actinometry give additional evidence that emission actinometry and mass spectrometry are powerful diagnostic tools to monitor stable and unstable species in discharges utilized for dry etching and polymer depositions. Mechanisms for end product formation and polymer deposition are also discussed.     

A straightforward method to extract the shunt resistance of photovoltaic cells from current-voltage characteristics of mounted arrays

A straightforward non-invasive method is proposed to accurately evaluate the shunt resistance of an elementary cell of a photovoltaic module connected in an installed string without requiring prior knowledge of the parameters of the intrinsic diodes. The approach relies on the measurement of the current-voltage characteristic of the whole string after intentionally shading the selected cell. Calibrated PSPICE simulations are employed to illustrate the method and test its reliability. As a case study, the shunt resistances of several cells belonging to a series array of 10 commercial panels are determined.     

Optical emission spectroscopy and actinometry in CCl4-Cl2 radiofrequency discharges

Radiofrequency discharges fed with CCl₄-Cl₂ mixtures have been studied in the pressure range 0.3 to 0.6 torr by means of emission spectroscopic actinometry with Ar, He, and N₂ as actinometers. Two different reactors, a parallel plate and a capacitively coupled tubular one, have been utilized for this study to obtain information for a large range of electron energy distributions. Analysis of the experimental results demonstrates the following: the utilization of actinometry and its range of validity, the importance of electron attachment to CCl_x species during the plasma decomposition process, and the effects of the presence of chlorine and “glowpolymer” in the discharge medium.     

Experimental measurements of majority and minority carrier lifetime profile in SI epilayers by the use of an improved OCVD method

In this letter, the first experimental results of a recently proposed technique for measuring the carrier lifetime profile are presented. The technique makes use of a four-terminal bipolar test structure to electrically define the epilayer volume where recombination occurs and employs the open circuit voltage decay method for lifetime parameters extraction. For the capability of the test structure to depurate measurements from the parasitic ohmic effects, the technique is able to measure the ambipolar and minority carrier lifetime along epilayer at high and low injection levels respectively. Comparisons of measurements with numerical simulations are reported to confirm the validity of the proposed technique.     

Parametric description of the effect of electron irradiation onrecombination lifetime in silicon layers: an experimental approach

The aim of this paper is to perform an experimental investigation on the effects of electron beam irradiation on the recombination lifetime of both p-type and n-type silicon layers in order to provide a set of parameters useful to model the recombination effects in semiconductor computer simulation package. To this goal, the authors propose to use a proper three-terminal test structure in order to extract these parameters directly from lifetime measurements along the silicon layers at different temperatures and at different injection levels by using the same silicon samples before and after the electron irradiation process in order to highlight the effects of the irradiation itself on the lifetime. The experimental results indicate that the electron irradiation is more effective for controlling the high-injection lifetime in p-type silicon than in an n-type one. The effect of the irradiation on lifetime can be basically taken into account by means of one energy level placed at 0.27 eV below the conduction band edge for both n-type and p-type material, with σ _p≅10 σ_n