Light-induced activation and deactivation of bulk defects in boron-doped float-zone silicon

In this paper, we present new insight in the degradation and subsequent recovery of charge carrier lifetime upon light soaking at 75 °C observed in float-zone silicon wafers. Variations of doping type, dielectric passivation schemes and thermal treatments after layer deposition were performed. The degradation was only observed for p-type float-zone silicon wafers passivated with passivation schemes involving silicon nitride layers. An influence of thermal treatments after deposition was found. N-type wafers did not degrade independent of their passivation scheme. Room temperature re-passivation experiments showed the degradation to affect the wafer bulk, and photoluminescence studies demonstrated fine lateral striations of effective lifetime. We conclude that the degradation is caused by bulk defects that might be related to hydrogen complexes

Experimental and theoretical study of oxygen precipitation and the resulting limitation of silicon solar cell wafers

Commercial silicon is prone to form silicon oxide precipitates during high-temperature treatments typical for solar cell production. Oxide precipitates can cause severe efficiency degradation in solar cells. We have developed a model describing the nucleation and growth of oxide precipitates that considers silicon self-interstitial defects and surface effects influencing the precipitate growth in ∼150 μm thick wafers during the solar cell processing. This kinetic model is calibrated with experiments that cause a well-defined and strong precipitate growth to give a prediction of the carrier lifetime limitation because of the oxide precipitates. We test the oxide precipitate model with scanning Fourier-transform infrared spectroscopy, selective etching, and lifetime measurements on typical Cz solar cell wafers before and after solar cell processes. Despite the relatively rough saw damaged etched surfaces and the thin wafers, we observe recurring ring patterns in the measurements of interstitial oxygen reductions, oxide precipitate etch pit density, and recombination activity by photoluminescence imaging. The concentration of precipitated oxygen correlates with the recombination activity and with the initial interstitial oxygen concentration. However, we found lifetime measurements to be a more sensitive technique to study oxide precipitates and using these we find smaller precipitates not detected by selective etching are very recombination active too. The measured concentrations of precipitated oxygen and lifetime agree fairly well with the predictions of the model

Electrically tunable Si-based THz photomodulator using dielectric/polymer surface gating

Silicon-based terahertz (THz) photomodulators suffer from a modulation speed limited by the lifetime of the charge carriers photoexcited in the silicon. We report a silicon-based THz photomodulator scheme offering real-time reconfiguration of the switching behavior by manipulation of effective charge carrier lifetime. Atomic layer deposition was used to coat silicon samples with dielectric layers to passivate the surfaces with a conductive polymer (PEDOT:PSS) subsequently deposited to enable electrical gating over the whole surface. The resulting gated photomodulators are characterized using photoconductance decay and photoluminescence imaging. A gated photomodulator with HfO2 passivation is then implemented into a THz time domain spectroscopy setup to demonstrate the potential for live photomodulation optimization during a single-pixel imaging experiment. We use the device to achieve a real-time improvement of the signal-to-noise ratio of the images by a factor of 8

Taking monocrystalline silicon to the ultimate lifetime limit

A central quantity to assess the high quality of monocrystalline silicon (on scales beyond mere purity) is the minority charge carrier lifetime. We demonstrate that the lifetime in high purity float zone material can be improved beyond existing observations, thanks to a deeper understanding of grown-in defects and how they can be permanently annihilated. In a first step we investigate the influence of several process sequences on the lifetime by applying a low temperature superacid passivation treatment. We find that a pre-treatment consisting of an oxidation at 1050 °C followed by a POCl3 diffusion at 900 °C can improve the lifetime by deactivating or eliminating grown-in defects. Then, pre-treated wafers of different float zone materials are passivated with three state-of-the-art layer stacks. Very high effective lifetime values are measured, thereby demonstrating the high quality of the surface passivation schemes and the pre-treated silicon wafers. The measured effective lifetimes exceed previous records, and we report an effective lifetime of 225 ms measured on a 200 µm thick 100 Ω cm n-type silicon wafer symmetrically passivated with a layer stack of a thin thermally grown oxide and a polycrystalline layer (the TOPCon layer stack)

Analiza ryzyka zdrowotnego i zarządzanie nim w łańcuchu logistyczno-produkcyjnym jako czynniki wpływające na jakość i bezpieczeństwo żywności w dwóch firmach spożywczych

The aim of this study was to identify risks in the quality and safety of food, and to indicate, basing on a risk analysis, the ways of managing potential risks in two different production profile enterprises of the food industry. It was found that potential hazards to the quality and safety for technological process as well as for the other links of the logistics chain were identified, and prevention procedures were established to minimize or completely eliminate these hazards. Moreover, the benefits of risk management were similar, and mainly felt in the constant increase of food producers’ awareness of the necessity of safe food production and increase of concern for the health and life of consumers. This in turn contributes to: development of staff competence, • improvement of logistic processes to better protect against external factors, unauthorized persons and side effects, • investments and implementation of new organisational solutions in warehouses and production areas

Experimental evidence of electron capture and emission from trap levels in Cz silicon

Up to now the existence of trap levels - defect levels in the forbidden band gap which temporary trap minority charge carriers - in Cz silicon was controversially discussed. We directly monitor the transient dynamics of the free electron density in the conduction band by the means of a time correlated single photon counting of photoluminescence. A variation of the experimental conditions reveals both a decrease of the electron density on a timescale of microseconds, which is not governed by recombination and an apparent generation of electrons on a scale of up to multiple seconds. We discuss that the transient dynamics may be excellently described by trap levels, providing strong evidence for their existence

Kinetics of carrier-induced degradation at elevated temperature in multicrystalline silicon solar cells

The degradation kinetics of multicrystalline silicon solar cells and wafers at elevated temperature (often termed “LeTID”) depend on the specific temperature and injection conditions. We apply different forward biases in the dark at a constant temperature of ~75 °C to industrial passivated emitter rear contacted (PERC) solar cells fabricated on p-type multicrystalline wafers from a variety of material producers and determine the degradation rate constant in dependence of the excess carrier density at the p-n junction. We find that whereas the specific material properties influence the degradation extent, the degradation rate constant is comparable for all materials but depends on the excess carrier concentration. This implies involvement of one electron in the rate-limiting step of LeTID defect formation. The result not only is an important contribution to elucidate the physical mechanism underlying LeTID, but can also be used as a guideline for devising degradation tests of multicrystalline silicon wafers and solar cells

The role of management reviews in the improvement of food quality and safety, customer service and quality management system in two selected enterprises of food industry

Celem pracy było zbadanie wpływu przeglądów zarządzania na różne obszary funkcjonowania dwóch zakładów produkcji żywności. Badania przeprowadzono w latach 2007-2013 w Zamrażalni Owoców i Warzyw Wiktor Tyc Sp. z o.o. oraz w okresie 2010-2014 w Credin Polska Sp. z o.o. − producenta wysokiej jakości mieszanek piekarsko-cukierniczych. W trakcie przeprowadzanych przeglądów zarządzania wykorzystywano wyniki audytów wewnętrznych i zewnętrznych, analizy działań korygujących i zapobiegawczych oraz reklamacji, jak również wywiady z pracownikami. Główne obszary objęte przeglądami zarządzania to strategiczne zarządzanie firmą, bezpieczeństwo zdrowotne żywności, proces realizacji zamówienia klienta wraz z oceną zadowolenia klienta oraz dalsze doskonalenie. Przeglądy zarządzania w naturalny sposób łączą szeroko pojętą tematykę sprzedażową z aspektem technologicznym, co w rezultacie prowadzi do spełniania wymagań klientów zarówno krajowych, jak i zagranicznych poprzez doskonalenie jakości, bezpieczeństwa żywności, poszukiwanie najlepszych rozwiązań produkcyjno-magazynowych. Inwestycje w technologię skutkowały zakupem nowych urządzeń i wprowadzeniem rozwiązań produkcyjnych, dzięki którym firmy były w stanie wprowadzać na rynek nowe/ulepszone produkty. Podsumowując, można stwierdzić, że przeglądy zarządzania w przedsiębiorstwie branży spożywczej przynoszą szereg wymiernych korzyści dotyczących wielu obszarów jego funkcjonowania.The aim of the study was to examine the impact of management reviews on different areas of operation of two plants of food production. The research was conducted for the period 2007 to 2013 in the Freezer for Fruit and Vegetables Viktor Tyc SP. z o.o. and Credin Poland SP. z o.o. manufacturer of high quality compound bakery-confectionery mixes. During the carried out management reviews the results of internal and external audits, analysis of corrective and preventive action and the claim, as well as interviews with employees were used. The main areas covered by the management surveys is a strategic company management, health safety of food, customer order processing, together with the assessment of customer satisfaction and continuous improvement. Management reviews naturally combine wide-ranging topics of sales with technology aspect which in turn leads to meet the requirements of clients, both domestic and foreign, through the continuous improvement of quality, food safety, the search for the best solutions to production and storage. Investments in technology have resulted in the purchase of new equipment and the introduction of manufacturing solutions, through which the companies were able to introduce new products to the market. It can be concluded that management reviews in a food production company bring a number of tangible benefits relating to all areas of its operation

Analysis of Temperature Dependent Surface Recombination Properties

To understand and maximize the annual energy output of silicon based photovoltaic modules beyond standard testing conditions (STC) it is of utmost importance to get insight into the temperature dependent device properties of silicon solar cells. In this study we demonstrate an approach which allows for both a global and a local characterization of effective recombination at the sample/air interface with varying injection and temperature. We investigate with SiNx or Al2O3 symmetrically passivated lifetime samples with temperature dependent lifetime measurements via modulated photoluminescence. Results show a decreasing effective surface recombination velocity with temperature and a significant injection-dependence. The results indicate a laterally varying and injection dependent temperature coefficient of the effective surface recombination. The common assumption of temperature-independent J0/ni2 for device simulations is demonstrated to cause errors of up to 30 percent. Our results can serve to improve temperature dependent device modelling for predicting and optimizing solar cell performance beyond STC as the proposed analysis is applicable to lifetime samples as well as wafers with diffused surfaces