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Ulrich Krumbein

Bio: Ulrich Krumbein is an academic researcher from ETH Zurich. The author has contributed to research in topics: Silicon & Quantum tunnelling. The author has an hindex of 4, co-authored 8 publications receiving 198 citations.

Papers
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Journal ArticleDOI
TL;DR: In this paper, the steady state recombination rate for two coupled defect levels and implemented the model into a device simulator, where the field effect was discussed in terms of tunnel assisted multiphonon capture or direct tunneling into the levels, respectively.
Abstract: We calculated the steady‐state recombination rate for two coupled defect levels and implemented the model into a device simulator. This model generalizes the familiar single‐level Shockley–Read–Hall (SRH) formula. If the intercenter transition probability vanishes, it reduces to the sum of two individual SRH rates, which are only linked via the band occupancies. The cases, where one of the levels or even both behave like traps in carrier capture, and the case of a rate‐limiting intercenter transition are derived from the general expression. The important feature of the model is a possible increased field effect which might lead to large excess currents. The field effect is discussed in terms of tunnel‐assisted multiphonon capture or direct tunneling into the levels, respectively. We show by means of numerical simulation that the large ideality factors found for liquid phase epitaxy grown diodes with weak intrinsic fields can be the result of a rapid direct charge transfer between donors and acceptors and ...

113 citations

Journal ArticleDOI
TL;DR: In this paper, a detailed analysis of the limiting loss mechanisms in PERL cells exhibiting independently confirmed 1-sun efficiencies of up to 23.0% was presented, based on measurements of the reflectance, quantum efficiency, dark and illuminated current-voltage (I-V) characteristics, and properties of the Si-SiO2 interfaces employed on these cells for surface passivation.
Abstract: The ‘‘passivated emitter and rear locally diffused’’ (PERL) silicon solar cell structure presently demonstrates the highest terrestrial performance of any silicon‐based solar cell. This paper presents a detailed investigation of the limiting loss mechanisms in PERL cells exhibiting independently confirmed 1‐sun efficiencies of up to 23.0%. Optical, resistive, and recombinative losses are all analyzed under the full range of solar cell operating conditions with the aid of two‐dimensional (2D) device simulations. The analysis is based on measurements of the reflectance, quantum efficiency, dark and illuminated current–voltage (I–V) characteristics, and properties of the Si–SiO2 interfaces employed on these cells for surface passivation. Through the use of the 2D simulations, particular attention has been paid to the magnitudes of the spatially resolved recombination losses in these cells. It is shown that approximately 50% of the recombination losses at the 1‐sun maximum power point occur in the base of the cells, followed by recombination losses at the rear and front oxidized surfaces (25% and <25%, respectively). The relatively low fill factors of PERL cells are principally a result of resistive losses; however, the recombination behavior in the base and at the rear surface also contributes. This work predicts that the efficiency of 23% PERL cells could be increased by about 0.7% absolute if ohmic losses were eliminated, a further 1.1% absolute if there were no reflection losses at the nonmetallized front surface regions, about 2.0% by introducing ideal light trapping and eliminating shading losses due to the front metallization, and by about 3.7% absolute if the device had no defect‐related recombination losses. New design rules for future efficiency improvements, evident from this analysis, are also presented.

81 citations

Book ChapterDOI
Ulrich Krumbein1, P. D. Yoder1, A. Benvenuti1, Andreas Schenk1, Wolfgang Fichtner1 
01 Jan 1995
TL;DR: In this article, a hierarchical CAD environment for realistic silicon device simulation, combining the utility of process, drift-diffusion/hydrodynamic, and Monte Carlo simulation in a unified platform is presented.
Abstract: We present a hierarchical CAD environment for realistic silicon device simulation, combining the utility of process, drift-diffusion/hydrodynamic, and Monte Carlo simulation in a unified platform Monte Carlo simulation results are presented for the cases of an NIN diode and a 40nm LDD-MOSFET, using information given by a hydrodynamic pre-processing step In addition we compare drift-diffusion, hydrodynamic and Monte Carlo results for an 05µm MOSFET whose geometry and doping profiles were generated by a 2-dimensional process simulation

4 citations

Proceedings ArticleDOI
02 Sep 1996
TL;DR: In this paper, the reverse characteristics of a 6H-SiC pin diode were investigated using the multi-dimensional device simulator DESSIS/sub-ISE/ discussing the contributions of different physical mechanisms to the blocking behavior and their temperature dependence.
Abstract: Silicon carbide is a promising material for special semiconductor applications, such as high-power and high-temperature devices. To date, much effort has been devoted to improving the process and device technology. With the progress in this field, the need for accurate modeling of device characteristics arises. This implies the formulation of proper physical models and their validation. We report on investigations of the reverse characteristics of a 6H-SiC pin diode using the multi-dimensional device simulator DESSIS/sub -ISE/ discussing the contributions of different physical mechanisms to the blocking behavior and their temperature dependence in the range of 300-623 K.

3 citations


Cited by
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Journal ArticleDOI
TL;DR: A review of surface passivation methods used since the 1970s, both on laboratory-type as well as industrial cells is presented in this paper, where a p-n junction and the subsequent passivation of the resulting silicon surface with plasma silicon nitride are presented.
Abstract: In the 1980s, advances in the passivation of both cell surfaces led to the first crystalline silicon solar cells with conversion efficiencies above 20%. With today's industry trend towards thinner wafers and higher cell efficiency, the passivation of the front and rear surfaces is now also becoming vitally important for commercial silicon cells. This paper presents a review of the surface passivation methods used since the 1970s, both on laboratory-type as well as industrial cells. Given the trend towards lower-cost (but also lower-quality) Si materials such as block-cast multicrystalline Si, ribbon Si or thin-film polycrystalline Si, the most promising surface passivation methods identified to date are the fabrication of a p–n junction and the subsequent passivation of the resulting silicon surface with plasma silicon nitride as this material, besides reducing surface recombination and reflection losses, additionally provides a very efficient passivation of bulk defects. Copyright © 2000 John Wiley & Sons, Ltd.

683 citations

Journal ArticleDOI
TL;DR: In this paper, the authors reviewed the current issues of numerical modeling of crystalline silicon solar cells and recommended that the widely used software in the PV community, PC1D, should be extended to Fermi-Dirac statistics.
Abstract: Current issues of numerical modeling of crystalline silicon solar cells are reviewed. Numerical modeling has been applied to Si solar cells since the early days of computer modeling and has recently become widely used in the photovoltaics (PV) industry. Simulations are used to analyze fabricated cells and to predict effects due to device changes. Hence, they may accelerate cell optimization and provide quantitative data e.g. of potentially possible improvements, which may form a base for the decision making on development strategies. However, to achieve sufficiently high prediction capabilities, several models had to be refined specifically to PV demands, such as the intrinsic carrier density, minority carrier mobility, recombination at passivated surfaces, and optical models. Currently, the most unresolved issue is the modeling of the emitter layer on textured surfaces, the hole minority carrier mobility, Auger recombination at low dopant densities and intermediate injection levels, and fine-tuned band parameters as a function of temperature. Also, it is recommended that the widely used software in the PV community, PC1D should be extended to Fermi-Dirac statistics.

274 citations

Book
01 Jan 2003
TL;DR: In this article, the authors reduced the three-dimensional transport in solar cells with periodically arranged rear point contacts to a one-dimensional calculation and derived an approximation for the series resistance.
Abstract: Summary of Chapter 2 The three-dimensional transport in solar cells with periodically arranged rear point contacts wassuccessfully reduced to a one-dimensional calculation. A new analytical formulation attributes aneffective surface recombination velocity S eff to the inhomogeneous rear surface. It is based on arelationship between the effective diffusion length and the series resistance in the base that be-came obvious after rigorously decoupling the transport problem. An approximation for this seriesresistance was derived which, for the first time, remains valid in every asymptote of the involvedparameters. Scaling laws helped to reduce the number of these parameters to only two; the cover-age fraction f and the period to cell thickness ratio l P . The final equation for the effective SRVreads fsf l f l f sls passP P metPeff −++−= − 11 1exp2arctan2 1 ππ,with s i = S i W / D , the SRV at the contacts S met and between the contacts S pass . The results are in goodagreement with three-dimensional simulations using a numerical Fourier-transform technique.A new method was found to discuss the effects of carrier lifetime variations in multicrystal-line solar cells without the need to assume a particular lifetime distribution. It consists in rules,expressed as a number

172 citations

Journal ArticleDOI
TL;DR: In this article, a remote-plasma SiN film is applied to the rear surface of the low-resistivity p-type substrates to achieve a surface recombination velocities as low as 4 cm s−1.
Abstract: Using a remote-plasma technique as opposed to the conventional direct-plasma technique, significant progress has been obtained at ISFH in the area of low-temperature surface passivation of p-type crystalline silicon solar cells by means of silicon nitride (SiN) films fabricated at 350–400°C in a plasma-enhanced chemical vapour deposition system. If applied to the rear surface of the low-resistivity p-type substrates, the remote-plasma SiN films provide outstanding surface recombination velocities (SRVs) as low as 4 cm s−1, which is by a clear margin the lowest value ever obtained on a low-resistivity p-Si wafer passivated by a solid film, including highest quality thermal oxides. Compared to direct-plasma SiN films or thermally grown oxides, the remote-plasma films not only provide significantly better SRVs on low-resistivity p-silicon wafers, but also an enormously improved stability against ultraviolet (UV) light. The potential of these remote-plasma silicon nitride films for silicon solar cell applications is further increased by the fact that they provide a surface passivation on phosphorus-diffused emitters which is comparable to high-quality thermal oxides. Furthermore, if combined with a thermal oxide and a caesium treatment, the films induce a UV-stable inversion-layer emitter of outstanding electronic quality. Due to the low deposition temperature and the high refraction index, these remote-plasma SiN films act as highly efficient surface-passivating antireflection coatings. Application of these films to cost-effective silicon solar cell designs presently under development at ISFH turned out to be most successful, as demonstrated by diffused p-n junction cells with efficiencies above 19%, by bifacial p-n junction cells with front and rear efficiencies above 18%, by mask-free evaporated p-n junction cells with efficiencies above 18% and by MIS inversion-layer cells with a new record efficiency of above 17%. All cells are found to be stable during a UV test corresponding to more than 4 years of glass-encapsulated outdoor operation. © 1997 John Wiley & Sons, Ltd.

171 citations

Journal ArticleDOI
TL;DR: A.P. and M.K. as discussed by the authors were on a Postdoctoral Fellowship from the Australian======ργεραραγεγαργαγατε βαγγακατα βαβγαβαγδαγβακaγαατaγγγεβατáγα-γαλαγaγaβαβθαγ�αγ-αγκαγiaγαἵ βαλγα β
Abstract: P.P.A. is on a Postdoctoral Fellowship from the Australian Research Council ~ARC!. The Center for Photovoltaic Engineering is supported by ARC’s Special Research Centres Scheme. A.C. and M.K. also acknowledge funding by the ARC.

170 citations