312 research outputs found

    Excellent passivation of germanium surfaces by POx/Al2O3 stacks

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    Passivation of germanium surfaces is vital for the application of germanium in next-generation electronic and photonic devices. In this work, it is demonstrated that stacks of phosphorous oxide and aluminum oxide (POx/Al2O3) provide excellent and stable passivation of germanium surfaces, with state-of-the-art surface recombination velocities down to 8.9 cm/s. The POx/Al2O3 stack also exhibits positive fixed charge on germanium, which makes it especially suited for passivation of highly doped n-type germanium surfaces. The chemical passivation mechanism is found to be related to the passivation of defects by hydrogen, which is mobilized by the formation of AlPO4 upon annealing. Furthermore, the GeOx interlayer is removed due to a kind of “self-cleaning” process during the deposition of POx/Al2O3 stacks on germanium, which may in part explain the excellent passivation quality. This self-cleaning of the interface may also allow simplified device fabrication workflows, as pretreatments may be omitted

    Passive macromodeling of one-port immittances via direct rational fitting of spectral factors

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    In this paper, we propose an algorithm for the generation of guaranteed passive state-space models of one-port immittances from finite frequency response samples. Differently from conventional approaches, which are based on a two-step process that first fits a rational function to the samples, and only in a second stage checks and enforces passivity via perturbation, our approach provides directly a guaranteed passive model. This is achieved by computing a stable rational approximation of a spectral factor associated to the immittance function under modeling. Several examples demonstrate the feasibility of the proposed technique

    On tuning passive black-box macromodels of LTI systems via adaptive weighting

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    This paper discusses various approaches for tuning the accuracy of rational macromodels obtained via black-box identification or approximation of sampled frequency responses of some unknown Linear and Time-Invariant system. Main emphasis is on embedding into the model extraction process some information on the nominal terminations that will be connected to the model during normal operation, so that the corresponding accuracy is optimized. This goal is achieved through an optimization based on a suitably defined cost function, which embeds frequency-dependent weights that are adaptively refined during the model construction. A similar procedure is applied in a postprocessing step for enforcing model passivity. The advantages of proposed algorithm are illustrated on a few application examples related to power distribution networks in electronic systems

    Silicon surface passivation by transparent conductive zinc oxide

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    Surface passivation is essential for high-efficiency crystalline silicon (c-Si) solar cells. Despite the common use of transparent conductive oxides (TCOs) in the field of solar cells, obtaining surface passivation by TCOs has thus far proven to be particularly challenging. In this work, we demonstrate outstanding passivation of c-Si surfaces by highly transparent conductive ZnO films prepared by atomic layer deposition. Effective surface recombination velocities as low as 4.8 cm/s and 11 cm/s are obtained on 3 Ω cm n- and p-type (100) c-Si, respectively. The high levels of surface passivation are achieved by a novel approach by using (i) an ultrathin SiO2 interface layer between ZnO and c-Si, (ii) a sacrificial Al2O3 capping layer on top of the ZnO film during forming gas annealing, and (iii) the extrinsic doping of the ZnO film by Al, B, or H. A combination of isotope labeling, secondary-ion mass spectrometry, and thermal effusion measurements showed that the sacrificial Al2O3 capping layer prevents the effusion of hydrogen from the crystalline ZnO and the underlying Si/SiO2 interface during annealing, which is critical in achieving surface passivation. After annealing, the Al2O3 capping layer can be removed from the ZnO film without impairing the high levels of surface passivation. The surface passivation levels increase with increased doping levels in ZnO, which can be attributed to field-effect passivation by a reduction in the surface hole concentration. The ZnO films of this work are suitable as a transparent conductor, an anti-reflection coating, and a surface passivation layer, which makes them particularly promising for simplifications in future solar cell manufacturing

    Een nieuwe atoomlaagdepositieproces voor efficiëntere zonnecellen

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    De prijs van zonnecellen is de laatste jaren aanzienlijk gedaald, waardoor geïnstalleerde zonnecellen tegenwoordig binnen afzienbare tijd zijn terugverdiend. Echter, om vooruitgang in het rendement en de kostprijs te kunnen blijven boeken zijn nieuwe technieken en materialen nodig. Een techniek die interessante mogelijkheden biedt voor de zonnecelindustrie is atoomlaagdepositie (ALD). Deze techniek wordt gebruikt om zeer dunne lagen, van slechts enkele nanometers dik, te ‘deponeren’ of ‘aan te groeien’. Op deze manier kunnen deze ‘films’ met zeer grote controle over de dikte én de ateriaaleigenschappen aangebracht worden. In dit artikel beschrijven we hoe we een nieuw ALDproces voor molybdeenoxide (MoOx) hebben ontwikkeld en hoe dit proces mogelijk gebruikt kan worden om het rendement te verhogen van zonnecellen van het zogenaamde type ‘silicium-heterojunctie’. We laten zien dat het materiaal zeer puur en transparant is en dat we goede prestaties kunnen verwachten voor een zonnecel met MoOx

    Low Temperature Atomic Layer Deposited Magnesium Oxide as a Passivating Electron Contact for c Si Based Solar Cells

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    In this article, we explore magnesium oxide MgO as electron selective contact layer in silicon heterojunction solar cells. We report on the successful deposition of MgO layers by atomic layer deposition at low temperatures amp; 8804;200 C using bis ethylcyclopentadienyl magnesium Mg CpEt 2 and H2O as precursors. Depositions were carried out on bare crystalline silicon c Si wafers and c Si wafers with an intrinsic amorphous hydrogenated silicon i aSi H passivation layer. The resulting interfacial properties, surface passivation quality, and contact resistivity were investigated. Upon initial deposition of MgO on an i aSi H c Si stack, the c Si surface passivation degrades drastically. However, with an additional annealing step of 5 min at 200 250 C, it is possible to reverse the degradation and even to achieve charge carrier lifetimes in excess of those achieved with an i aSi H alone. Furthermore, we show that MgO forms an ohmic contact with both MgO i aSi H c Si and MgO c Si stacks, and we demonstrate solar cells using both types of stacks as electron contact layer

    Depositie van polykristallijn silicium voor dunne-film zonnecellen

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    In dit artikel beschrijven we de succesvolle depositie door middel van een expanderend thermisch plasma (ETP) van polykristallijn silicium (poly-Si), een aantrekkkelijk materiaal voor dunne-film zonnencellen

    Implementation of vacuum-assisted excision as a management option for benign and high-risk breast lesions

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    Objective: Previous studies have shown that vacuum-assisted excision (VAE) is a safe and effective alternative for surgical excision (SE) of benign breast lesions. However, the use of VAE in high-risk lesions is controver-sial and guidelines are ambiguous. This study describes the impact of the implementation of VAE in terms of management and outcomes compared to a cohort before implementation. Methods: A single centre retrospective study with two cohorts: ‘before’ and ‘after’ implementation of VAE was performed. All patients with a benign or high-risk lesion treated by VAE or SE between 2016 and 2019 were included. Excision, complication, and upgrade rates were compared between both cohorts. Cox regression was used for the evaluation of recurrences and re-excisions. Results: The overall excision rate of all benign and high-risk lesions was comparable in both cohorts (17% vs 16%, p = 0.700). After implementation, benign lesions were significantly more often managed by VAE (101/151, 67%, p &lt; 0.001). Re-excision, recurrence, and complication rates were low and comparable between cohorts (4.3% vs 3.9%, p &gt; 0.999; 3.0 vs 2.0%, p = 0.683; 3.4 vs 6.6%, p = 0.289, respectively). Conclusion: SE could safely be replaced by VAE in 58% of patients treated for a benign or high-risk lesion. With this shift in management, the use of operating rooms and general anaesthesia can safely be omitted in this patient group. Further research on high-risk lesions is warranted since our data are exploratory. Advances in knowledge: This study provides supportive data for the use of VAE as a management option for both benign (up to 5 cm) and high-risk lesions. Outcomes on re-excision, recurrence should be confirmed in prospective studies especially in high-risk lesions.</p
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