Excellent passivation of germanium surfaces by POx/Al2O3 stacks

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

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

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

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

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

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

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

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

Metallothioneins as dynamic markers for brain disease in lysosomal disorders

Objective: To facilitate development of novel disease-modifying therapies for lysosomal storage disorder (LSDs) characterized by nervous system involvement such as metachromatic leukodystrophy (MLD), molecular markers for monitoring disease progression and therapeutic response are needed. To this end, we sought to identify blood transcripts associated with the progression of MLD. Methods: Genome-wide expression analysis was performed in primary T lymphocytes of 24 patients with MLD compared to 24 age- and sex-matched healthy controls. Genes associated with MLD were identified, confirmed on a quantitative polymerase chain reaction platform, and replicated in an independent patient cohort. mRNA and protein expression of the prioritized gene family of metallothioneins was evaluated in postmortem patient brains and in mouse models representing 6 other LSDs. Metallothionein expression during disease progression and in response to specific treatment was evaluated in 1 of the tested LSD mouse models. Finally, a set of in vitro studies was planned to dissect the biological functions exerted by this class of molecules. Results: Metallothionein genes were significantly overexpressed in T lymphocytes and brain of patients with MLD and generally marked nervous tissue damage in the LSDs here evaluated. Overexpression of metallothioneins correlated with measures of disease progression in mice and patients, whereas their levels decreased in mice upon therapeutic treatment. In vitro studies indicated that metallothionein expression is regulated in response to oxidative stress and inflammation, which are biochemical hallmarks of lysosomal storage diseases. Interpretation Metallothioneins are potential markers of neurologic disease processes and treatment response in LSDs