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Overtemperature occurring in silicon solar panels subject to partial shadowing are reduced by means of a new bypass circuit. The circuit exploits a series connected power MOSFET which sustains part of the reverse voltage developing across the shaded solar cell. Neither power supply nor control logic are required, resulting in an appealing advantage with respect the other active bypass circuits. Experiments performed on a commercial mono-crystalline solar panel evidenced a reduction of the reverse voltage across a shaded cell, if compared with the traditional bypass diode, of about 50%, corresponding to a temperature decease approaching 22°C.

The reduction of the trap density at the SiC/SiO2 interface of a SiC metal–oxide–semiconductor field-effect transistor (MOSFET) is still an open issue for development of the next generation. Since TCAD simulations are one of the most powerful tools adopted in the field of power semiconductor devices, in this article, we define the guidelines for the calibration of the TCAD model from the point of view of the interface traps modeling. We have carried out a qualitative analysis of the effect of the SiC/SiO2 interface traps properties on the $C$ – $V$ curve by means of TCAD simulations, to support the interpretation of the experimental $C$ – $V$ curves of a SiC MOSFET. A new approach for the simulation of the $C$ – $V$ curves of a SiC MOSFET is proposed as well. The aim of this article is the analysis of the effect of the SiC/SiO2 interface traps on the $C$ – $V$ curve by means of TCAD simulations.

The paper investigates the detrimental effect of nonuniform and uniform crack distributions over a solar cell in terms of open-circuit voltage (V_oc), short-circuit current density (J_sc), and output power, the latter under a wide range of irradiance conditions. The experimental procedure to detect the cracks relies on electroluminescence imaging, which is nondestructive and requires a relatively low amount of time. The Griddler software is adopted to translate the EL-taken image into V_oc and J_sc maps. The main findings can be summarized as follows: (i) the nonuniformly- and uniformly-cracked cells are both jeopardized in terms of output power; (ii) the loss corresponding to the cell with nonuniform distribution of cracks is increasingly higher than the uniformly-cracked counterpart as the irradiance hitting the cells grows, and (iii) all cells affected by nonuniform cracks are severely damaged in terms of fingers and rear busbar, which concur to limit the maximum output current.

We report a theoretical study about the performances of graphene on semiconductor Schottky barrier solar cells with the aim to show the potentiality of this kind of device. The simulations are carried by a generalized equivalent circuit model, where the circuital parameters are strictly dependent on the physical properties of the graphene and semiconductor which form the Schottky junction. We have realized graphene samples and characterized them by optical and atomic force microscopy, and Raman spectroscopy. Capacitance–voltage measurements have been made on some “ad hoc” graphene based devices in order to obtain graphene workfunction, a very essential physical parameter. The estimated value is compatible with four layer graphene. This result is in agreement with the morphological characterizations of our material.

The main aspects of the sol–gel synthesis of ZnO thin films were critically examined with particular reference to the optimization of the process parameters that influence specific properties of the films, such as the transparency, the crystallization behavior and the electrical resistivity. Starting from zinc acetate dihydrate, anhydrous ethanol and triethanolamine, a valuable sol–gel route was set. This route allowed the preparation of transparent ZnO thin films by dip-coating. Triethanolamine, thanks to its high chelating efficiency towards Zn2+, permitted to prepare stable zinc acetate dihydrate solutions wholly at room temperature. The structural, optical and morphological characteristics of the films were examined by glancing incidence X-ray diffraction, UV–vis spectroscopy and atomic force microscopy. Single layer films, with a thickness of about 120 nm, characterized by a high adhesion force (about 140 Kg cm−2), were obtained. The crystallization behavior of dip-coated amorphous films was explored in the 500–600 °C range; polycrystalline films, formed by randomly oriented ZnO nanocrystals (about 20 nm), with an average transmittance higher than 90% in the visible region, were obtained. Finally, a strong influence of annealing environment on electrical resistivity was observed.

This paper deals with the modeling of series resistance components in silicon concentrator solar cells. The main components of the macroscopic series resistance are analyzed by means of one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) numerical simulations. It is shown that the contribution of the lateral current flux, flowing along the emitter region, and of the transverse current flux, flowing along the metal grid, cannot be neglected and, hence, the operation of solar cells subjected to high current densities cannot be described by simple one-dimensional models. The percentage weight of 2D and 3D components on the total value of the series resistance is evaluated and rules for the proper design of the cell geometries are given. An analysis of the effectiveness of the most popular methods for the extraction of the series resistance from the I–V curves of solar cells is also proposed.

In this work, a novel test structure to measure the surface or interface recombination velocity is presented that can be used to measure the effect of different surface treatments made on an exposed surface after the test device has been fabricated. The test device is made by a vertical p + nn + injecting diode, and by a floating n + region, that acts as a sense terminal on the top surface. It can be shown that the voltage measured between the top floating terminal and the bottom, when the diode is forward biased, depends on the recombination velocity at surface. If this surface is exposed to subsequent processes (RIE etching, oxide deposition, etc.), the recombination properties of the new transition can be analysed. Two-dimensional simulations of the test structure operation have been performed, a variation of two orders of magnitude of the sense voltage is induced by varying S in the typical range of interest between 10 2 and 10 6 cm s −1 , demonstrating the high sensitivity of the proposed method.

The operation of micro-optoelectronic devices relies on optical properties of materials, first of all the wavelength dependent refractive index. Standard measurement techniques are often prone to significant ambiguities caused by the periodic nature of the optical response. In this paper we propose a procedure which exploits transmittance measurements, performed at variable light incidence angle, to reconstruct the complex refractive index as a function of the wavelength. Experiments performed on a thin TCO layer prove the reliability of the method. © 2014 IEEE.

Electronic switching devices often requires some form of post processing to adjust, with high spatial resolution, the value of the recombination lifetime. The most selective killing technique used so far exploits high energy helium implantation. The main obstacle to the proper modeling of implantation effects comes from the unavailability of reliable measurement techniques able to “look” into the device to measure the local value of the lifetime. In this paper the differential technique for lifetime profile measurements is applied to materials suitable for the fabrication of planar IGBTs.

The sol-gel synthesis of undoped and B- or Al-doped ZnO thin films were critically examined with particular reference to the influence of the pH of the reaction medium on some of their specific characteristics, such as thickness, morphology, doping level and optical properties, in view of their application in the photovoltaic field. Using triethanolamine (TEA) as chelating agent, a range of basic pH from 7.66 to 8.76 was explored starting from a very concentrated zinc acetate dehydrate (ZAD) solution in ethanol, [Zn2+] = 1.0 M, and keeping the ZAD/TEA = 1. A more basic environment gives more porous films whose thickness and crystallinity are higher than those achieved at lower pH. It was found that the morphology, as well as the sheet resistance (Rs) of films, depends on both pH and doping. Increasing the pH the Rs decreases for both undoped and doped films. At a certain pH undoped films exhibit a granular microstructure and lower Rs than B- or Al-doped films which exhibit a finer texture, characterized by a lower porosity. Optical properties strongly depend on the pH as well. Increasing the pH, a noticeable blue shift effect was observed, that was attributed mainly to structural changes and to a lesser extent to the Burnstein-Moss effect. © 2014 Elsevier B.V.

TCO (Transparent Conductive Oxides) layers often exhibit very rough surfaces and their optical properties, can not be described by one dimensional analytical models and numerical approaches must be adopted. However, computational time becomes, often, too large. In this paper we propose an automated procedure, based on the interaction between MATLAB and the Sentaurus TCAD environment which finds, in a generic rough surface, the smallest area characterized by the same statistical features of the whole surface so that full 3D analysis can be performed. © 2014 IEEE.

A high sensitivity, pump–probe optical method to measure the bulk minority-carrier lifetime and surface recombination velocity in silicon is proposed. A pig-tailed 1.55 μm CW laser diode is used to detect the transient of the excess carriers generated by a short Nd:YAG laser pulse. The probe beam is launched parallel to the sample surface while the pump beam uniformly illuminates the sample perpendicular to its surface. Separation between bulk lifetime and surface recombination velocity is achieved by performing the measurement on samples of different thickness. Experimental results indicate that separation of bulk and surface contribution is feasible in a wide range of surface recombination velocities thus making this method suitable to investigate the effects of surface passivation techniques.

In this paper, we present a quantitative study of the effects of lifetime engineering treatments on the switching operation of power diodes, with special regards to the whole energy consumption. Not only single platinum diffusion and helium implantation processes, but also the combined effects for both treatments have been analyzed. Results show that care must be taken when choosing the lifetime treatment because univocal rules are difficult to draw.

In this paper, a study of the effects on both lifetime and resistivity, induced by helium implantation processes, is presented. A wide range of implantation energies (from 3.5 MeV to 5.8 MeV) and doses (from 1middot108 atm/cm2 to 2middot1011 atm/cm2) is considered and, for each of them, the resistivity profile and the lifetime profile are measured and compared with that of the unprocessed material. Moreover, the temperature dependence of that profile is analysed in the usual operation range of power devices. Results show that a high helium dose not only reduces the recombination lifetime but significatively affects the resistivity too. The temperature dependence of the two parameters is such that they play different roles at high or low temperature

In this paper we propose an all electrical resistivity profiling technique specially suitable to characterise the effects of ion implantation processes used in lifetime engineering processes. The technique is based on the operation of a simple three terminals test device, already present in most practical structures. The theory of the measurement method is presented and two-dimensional simulations showing the reliability of the method are also shown. Moreover, experimental results gained on helium implanted devices are given. In particular, measurements performed at different temperatures have permitted to identify a trap center with an energy level located at Ec-0.23 eV as the responsible for the changes in the resistivity of helium implanted devices.

A new test structure for the recombination lifetime profile measurement has been designed and applied, for the first time, to characterize very thin (4 /spl mu/m) silicon epitaxial layers. The results of our analysis have shown how the lifetime behavior, at room temperature, is clearly position dependent its value being influenced by different recombination centers. Moreover, two distinct recombination centers have been identified, the first one related to the dopant (arsenic in our case) and the second one induced by the process steps required to realize the test structure itself.

The distribution of recombination centers induced in Si epi-substrates by helium (He) implantation is obtained for the first time by direct measurement of local recombination lifetime profile along the layer, using the ac differential lifetime profiling technique. The different energy levels of the recombination centers induced by He implantation at different doses and energies have been extracted, as a function of the position in the layer, by temperature scanning of the lifetime profiles. The lifetime measurements clearly demonstrate the presence of a secondary defect distribution that extend from the region of maximum primary damage both at lower and higher depths respect to the stopping range depth, due to the relatively large concentration of primary defects created near the stopping range, and give a coherent picture of the effects of He implant on the "local" lifetime.

Radioactive ion implantation allows non‐contacting, online wear measurements with sub micrometric sensitivity to be performed, by monitoring the removed and/or residual activity on parts subject to wear. Comparative studies of different materials, including those who exhibit a low resistance to radiation damage, can be easily performed by means of this technique. A project has started at the TTT3 tandem of the University “Federico II” in Naples, Italy, in order to exploit such technique using a 7Be ion beam, that was developed to study the astrophysical important reaction 7Be(p,γ)8B. The 7Be ion beam is produced using a ion sputter source and accelerated to an energy up to 8.0 MeV. A novel setup allows control of the implanted ion depth distribution, and is a crucial point for the application of this technique. The 7Be ion beam production and implantation procedures are discussed. Finally, the results of some test measurements are presented.

An analytical model of the I – V input curves of normally on JFET structures for an arbitrary drain voltage is proposed. The model is capable to predict the occurrence of a negative resistance in the curves in agreement with numerical simulations and experiments. It is shown that, similarly to the unijunction transistor, the negative resistance is determined by the variation of the ohmic drain voltage occurring in the base as the gate voltage reaches the onset value of the conductivity modulation regime. Moreover the model can be considered the basic theory of the experimental method proposed [Solid-State Electron 43(7) (1999) 1201] for measuring the series resistance of lateral diodes.

Experimental measurements of the recombination lifetime profile induced by proton implantation processes are presented. Results show the capability of the differential technique to monitor lifetime engineering processes.

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.

SummaryModelling mobility degradation due to carrier-carrier scattering is of utmost importance for the analysis and simulation of power bipolar devices. Unfortunately, there is a large disagreement among the several theoretical mobility models available in literature (see Fig.1).In addition, the experimental approaches proposed up to date for mobility extraction are based on measurements performed on thick p-i-n diodes, resulting in large power dissipation with significant device heating and rough estimation of injection level.In this paper we present a new approach to measure the conductivity mobility dependence on the injection level, based on electrical measurements performed on a three-terminal test structure. The new technique overcomes most of the intrinsic limitations of previously proposed approaches and has the unique capability of extracting the injection-level dependence of both hole and electron mobilities.Two-dimensional numerical simulations and experimental results obtained both on n-type ...

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. >