Minority carrier lifetime in silicon photovoltaics : the effect of oxygen precipitation

Single-crystal Czochralski silicon used for photovoltaics is typically supersaturated with interstitial oxygen at temperatures just below the melting point. Oxide precipitates therefore can form during ingot cooling and cell processing, and nucleation sites are typically vacancy-rich regions. Oxygen precipitation gives rise to recombination centres, which can reduce cell efficiencies by as much as 4% (absolute). We have studied the recombination behaviour in p-type and n-type monocrystalline silicon with a range of doping levels intentionally processed to contain oxide precipitates with a range of densities, sizes and morphologies. We analyse injection-dependent minority carrier lifetime measurements to give a full parameterisation of the recombination activity in terms of Shockley–Read–Hall statistics. We intentionally contaminate specimens with iron, and show recombination activity arises from iron segregated to oxide precipitates and surrounding defects. We find that phosphorus diffusion gettering reduces the recombination activity of the precipitates to some extent. We also find that bulk iron is preferentially gettered to the phosphorus diffused layer rather than to oxide precipitates

Роль активных форм кислорода в патогенезе дисфункции адипоцитов при метаболическом синдроме: перспективы фармакологической коррекции

It is established that oxidative stress induces insulin resistance of adipocytes, increases secretion leptin, IL-6, TNF-α by adipocytes. Adiponectin secretion by adipocytes is reduced after the action of reactive oxygen species. Metabolic syndrome contributes to oxidative stress in adipose tissue, on the one hand due to the activation of production of reactive oxygen species by adipocyte NADPH-oxidase, and on the other hand by reducing the antioxidant defense adipocytes. It is found that obesity itself can induce oxidative stress. Chronic stress, glucocorticoids, mineralocorticoids, angiotensin-II, TNF-α play an important role in the pathogenesis of oxidative stress of adipocytes. Metformin remains the cure for the treatment of insulin resistance. The positive results in the treatment of metabolic syndrome by losartan were obtained. Antioxidants and flavonoids exhibit a positive impact on the course of the experimental metabolic syndrome.Установлено, что окислительный стресс вызывает инсулинорезистентность адипоцитов, способствует увеличению секреции адипоцитами лептина, ИЛ-6, ФНО-α. Под действием активных форм кислорода снижается секреция адипоцитами адипонектина. Метаболический синдром способствует окислительному стрессу в жировой ткани с одной стороны – за счет активации продукции активных форм кислорода НАДФН-оксидазой, а с другой – в результате снижения антиоксидантной защиты адипоцитов. Установлено, что ожирение само по себе может вызывать окислительный стресс. В патогенезе окислительного стресса адипоцитов важную роль играет хронический стресс, глюкокортикоиды, минералокортикоиды, ангиотензин-II, ФНО-α. Средством выбора при лечении инсулинорезистентности остаётся метформин. Получены положительные результаты при лечении метаболического синдрома лозартаном. Антиоксиданты и флавоноиды оказывают положительное влияние на течение экспериментального метаболического синдрома

The annealing mechanism of the radiation-induced vacancy-oxygen defect in silicon

Annealing experiments on the VO defect (the A-centre) produced by radiation in silicon-reported long ago-have been re-examined in order to deduce the two most important properties of VO: its diffusivity and the equilibrium constant for VO dissociation into V + O. The loss rate of VO is accounted for by two major reactions. One is the conventional reaction of the trapping of mobile VO by oxygen, thus producing VO 2. The other is an annihilation of vacancies, which coexist in an equilibrium ratio with VO, by radiation-produced interstitial point defects. In some cases, a minor reaction, VO + V, should also be taken into account. The emerging minor defects V 2O are also highly mobile. They partially dissociate back and partially get trapped by oxygen producing stable V 2O 2 defects. © 2012 American Institute of Physics

Production of vacancy-oxygen defect in electron irradiated silicon in the presence of self-interstitial-trapping impurities

The enhancement by carbon of vacancy-oxygen (VO) defect formation in electron irradiated silicon was investigated using many samples of various carbon contents. The effect of carbon is well described by a simple analytical model of competing trapping of self-interstitials by VO and by carbon (and by emerging carbon-related defects like CiOi and IC iOi). The trapping ratio by Cs and by VO was determined to be about 0.9, and the optical calibration coefficients for C iOi and ICiOi were deduced. In crystals containing a high concentration of Ge, germanium also acts as a self-interstitial trapping impurity and, thus, enhances VO production. The trapping efficiency of Ge is 1000 times less than that of carbon. © 2011 American Institute of Physics