Junction formation and current transport mechanisms in hybrid n-Si/PEDOT:PSS solar cells

We investigated hybrid inorganic-organic solar cells combining monocrystalline n-type silicon (n- Si) and a highly conductive polymer poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS). The build-in potential, photo- and dark saturation current at this hybrid interface are monitored for varying n-Si doping concentrations. We corroborate that a high build-in potential forms at the hybrid junction leading to strong inversion of the n-Si surface. By extracting work function and valence band edge of the polymer from ultraviolet photoelectron spectroscopy, a band diagram of the hybrid n-Si/PEDOT:PSS heterojunction is presented. The current- voltage characteristics were analyzed using Schottky and abrupt pn-junction models. The magnitude as well as the dependence of dark saturation current on n-Si doping concentration proves that the transport is governed by diffusion of minority charge carriers in the n-Si and not by thermionic emission of majorities over a Schottky barrier. This leads to a comprehensive explanation of the high observed open-circuit voltages of up to 634 mV connected to high conversion efficiency of almost 14%, even for simple planar device structures without antireflection coating or optimized contacts. The presented work clearly shows that PEDOT:PSS forms a hybrid heterojunction with n-Si behaving similar to a conventional pn-junction and not, like commonly assumed, a Schottky junction

Density functional theory calculation of the properties of carbon vacancy defects in silicon carbide

As a promisingmaterial for quantumtechnology, silicon carbide (SiC) has attracted great interest inmaterials science. Carbon vacancy is a dominant defect in 4H-SiC. Thus, understanding the properties of this defect is critical to its application, and the atomic and electronic structures of the defects needs to be identified. In this study, density functional theorywas used to characterize the carbon vacancy defects in hexagonal (h) and cubic (k) lattice sites. The zero-phonon line energies, hyperfine tensors, and formation energies of carbon vacancies with different charge states (2-, -, 0,+ and 2+) in different supercells (72, 128, 400 and 576 atoms)were calculated using standard Perdew-Burke-Ernzerhof and Heyd-Scuseria-Ernzerhof methods. Results show that the zero-phonon line energies of carbon vacancy defects are much lower than those of divacancy defects, indicating that the former is more likely to reach the excited state than the latter. The hyperfine tensors of VC+(h) and VC+(k) were calculated. Comparison of the calculated hyperfine tensor with the experimental results indicates the existence of carbon vacancies in SiC lattice. The calculation of formation energy shows that the most stable carbon vacancy defects in the material are VC2+(k), VC+(k), VC(k), VC-(k) and VC2-(k) as the electronic chemical potential increases.Peer reviewe

MD simulation study on defect evolution and doping efficiency of p-type doping of 3C-SiC by Al ion implantation with subsequent annealing

We use molecular dynamics (MD) simulation with numerical characterisation and statistical analysis to study the mechanisms of damage evolution and p-type doping efficiency by aluminum (Al) ion implantation into 3C silicon carbide (SiC) with subsequent annealing. By incorporating the electronic stopping power for implantation, a more accurate description of the atomic-scale mechanisms of damage evolution and distribution in SiC can be obtained. The simulation results show a novel observation that the recrystallization process occurs in the region below the subsurface layer, and develops from amorphous-crystalline interface to the damage center region, which is a new insight into previously published studies. During surface recrystallization, significant compressive stress concentration occurs, and more structural phase transition atoms and dislocations formed at the damage-rich-crystalline interface. Another point of interest is that for low-dose implantation, more implantation-induced defects hamper the doping efficiency. Correspondingly, the correlation between lattice damage and doping efficiency becomes weaker as the implant dose increases under the same annealing conditions. Our simulation also predicts that annealing after high temperature (HT) implantation is more likely to lead to the formation of carbon vacancies (V-C).Peer reviewe

Nanocutting mechanism of 6H-SiC investigated by scanning electron microscope online observation and stress-assisted and ion implant-assisted approaches

Nanocutting mechanism of single crystal 6H-SiC is investigated through a novel scanning electron microscope setup in this paper. Various undeformed chip thicknesses on (0001) orientation are adopted in the nanocutting experiments. Phase transformation and dislocation activities involved in the 6H-SiC nanocutting process are also characterized and analyzed. Two methods of stress-assisted and ion implant-assisted nanocutting are studied to improve 6H-SiC ductile machining ability. Results show that stress-assisted method can effectively decrease the hydrostatic stress and help to activate dislocation motion and ductile machining; ion implant-induced damages are helpful to improve the ductile machining ability from MD simulation and continuous nanocutting experiments under the online observation platform.Peer reviewe

Cardiac output states in patients with severe functional tricuspid regurgitation: impact on treatment success and prognosis

Aims To investigate whether there is evidence for distinct cardiac output (CO) based phenotypes in patients with chronic right heart failure associated with severe tricuspid regurgitation (TR) and to characterize their impact on TR treatment and outcome. Methods and results A total of 132 patients underwent isolated transcatheter tricuspid valve repair (TTVR) for functional TR at two centres. Patients were clustered according to k-means clustering into low [cardiac index (CI)  2.6 L/min/m2) clusters. All-cause mortality and clinical characteristics during follow-up were compared among different CO clusters. Mortality rates were highest for patients in a low (24%) and high CO state (42%, log-rank P < 0.001). High CO state patients were characterized by larger inferior vena cava diameters (P = 0.003), reduced liver function, higher incidence of ascites (P = 0.006) and markedly reduced systemic vascular resistance (P < 0.001) as compared to TTVR patients in other CO states. Despite comparable procedural success rates, the extent of changes in right atrial pressures (P = 0.01) and right ventricular dimensions (P < 0.001) per decrease in regurgitant volume following TTVR was less pronounced in high CO state patients as compared to other CO states. Successful TTVR was associated with the smallest prognostic benefit among low and high CO state patients. Conclusions Patients with chronic right heart failure and severe TR display distinct CO states. The high CO state is characterized by advanced congestive hepatopathy, a substantial decrease in peripheral vascular tone, a lack of response of central venous pressures to TR reduction, and worse prognosis. These data are relevant to the pathophysiological understanding and management of this important clinical syndrome. Graphical Abstract Proposed mechanism of hypercirculatory tricuspid regurgitation. Tricuspid regurgitation related backward failure causes liver congestion and dysfunction with portal hypertension and reduced washout of vasoactive substances. Consequent splanchnic and peripheral vasodilatation alongside with reduced renal blood flow results in renin–angiotensin–aldosterone system (RAAS) activation and sympathetic overactivation. The sympathetic drive and volume retention lead to further capacitance depletion and volume overload, eventually resulting in a high cardiac output state, with limited preload reduction and prognostic benefit following transcatheter tricuspid valve repair. The alterations in the graph should be interpreted as simultaneous interaction rather than a timeline. Continuous lines indicate findings in the present study. Dashed lines express currently accepted mechanistical considerations. AP, alkaline phosphatase; γGT, gamma-glutamyl-transferase; RA, right atrium; RV, right ventricle

Topic review : Application of raman spectroscopy characterization in micro/nano-machining

The defects and subsurface damages induced by crystal growth and micro/nano-machining have a significant impact on the functional performance of machined products. Raman spectroscopy is an efficient, powerful, and non-destructive testing method to characterize these defects and subsurface damages. This paper aims to review the fundamentals and applications of Raman spectroscopy on the characterization of defects and subsurface damages in micro/nano-machining. Firstly, the principle and several critical parameters (such as penetration depth, laser spot size, and so on) involved in the Raman characterization are introduced. Then, the mechanism of Raman spectroscopy for detection of defects and subsurface damages is discussed. The Raman spectroscopy characterization of semiconductor materials’ stacking faults, phase transformation, and residual stress in micro/nano-machining is discussed in detail. Identification and characterization of phase transformation and stacking faults for Si and SiC is feasible using the information of new Raman bands. Based on the Raman band position shift and Raman intensity ratio, Raman spectroscopy can be used to quantitatively calculate the residual stress and the thickness of the subsurface damage layer of semiconductor materials. The Tip-Enhanced Raman Spectroscopy (TERS) technique is helpful to dramatically enhance the Raman scattering signal at weak damages and it is considered as a promising research field

Petri Net computational modelling of Langerhans cell Interferon Regulatory Factor Network predicts their role in T cell activation

Langerhans cells (LCs) are able to orchestrate adaptive immune responses in the skin by interpreting the microenvironmental context in which they encounter foreign substances, but the regulatory basis for this has not been established. Utilising systems immunology approaches combining in silico modelling of a reconstructed gene regulatory network (GRN) with in vitro validation of the predictions, we sought to determine the mechanisms of regulation of immune responses in human primary LCs. The key role of Interferon regulatory factors (IRFs) as controllers of the human Langerhans cell response to epidermal cytokines was revealed by whole transcriptome analysis. Applying Boolean logic we assembled a Petri net-based model of the IRF-GRN which provides molecular pathway predictions for the induction of different transcriptional programmes in LCs. In silico simulations performed after model parameterisation with transcription factor expression values predicted that human LC activation of antigen-specific CD8 T cells would be differentially regulated by epidermal cytokine induction of specific IRF-controlled pathways. This was confirmed by in vitro measurement of IFN-g production by activated T cells. As a proof of concept, this approach shows that stochastic modelling of a specific immune networks renders transcriptome data valuable for the prediction of functional outcomes of immune responses

Der Geologische Dienst in Sachsen: Festband zum Jubiläum 150 Jahre Landesgeologie

Der Geologische Dienst von Sachsen feiert im Jahr 2022 sein 150-jähriges Jubiläum – am 6. April 1872 wurde die Geologische Landesuntersuchung im Königreich Sachsen gegründet. Auf 153 Seiten der Reihe „Geoprofil“ werden Einblicke in die Arbeit des Geologischen Dienstes im LfULG, seinen Aufgaben und die Dienste als zuständige Fachbehörde gegeben. Die elf Einzelbeiträge zeigen die aktuellen Herausforderungen und Chancen, die sich aus den Themenbereichen Umwelt, Naturschutz und Geologie für Sachsen stellen. Im Einzelnen geht es in den Beiträgen um die sächsische Rohstoffstrategie, die Suche nach einem Endlagerstandort für radioaktive Abfälle, Erdwärme, Hydrogeologie, die Eisenbahn Neubaustrecke Dresden – Prag, Naturgefahren, das geowissenschaftliche Archiv, Träger öffentlicher Belange (TöB), Geoparks und einen Blick in die 150 jährige Geschichte. Redaktionsschluss: 30.11.202

Photo current spectroscopy of silicon in the bulk and at the interface with silicon dioxide

Die vorliegende Arbeit befasst sich mit umfassenden Untersuchungen zur Injektionsabhängigkeit von Photostrom-Messungen. Mit dem konventionellen Elymat-Verfahren wurde die Injektionsabhängigkeit der Ladungsträgerlebensdauer von Eisen-kontaminierten bordotierten Siliciumproben experimentell ermittelt und durch zweidimensionale Simulationen verifiziert. Die dabei gewonnenen Ergebnisse sind von grundlegender Bedeutung für die ebenfalls erfolgte injektionsabhängige Charakterisierung von Isolator/Silicium-Strukturen mit einem modifizierten Elymat-Verfahren. Entscheidend für die korrekte Messung von Niederinjektionslebensdauern ist eine ausreichende Passivierung der Halbleiteroberfläche. Es konnte gezeigt werden, dass die beim konventionellen Elymat-Verfahren verwendete Oberflächenpassivierung durch 1%ige Flusssäure nicht effektiv genug ist, während die Lebensdauern mit Hilfe der elektrostatischen Passivierung des modifizierten Elymat-Verfahrens im gesamten Injektionsbereich sehr genau bestimmt werden können. Gerade bei niedriger Injektion kann dieser Effekt selbst mit natürlichem Oxid als Isolator genutzt werden. Die Lebensdauerspektroskopie an Eisen-kontaminierten Siliciumproben mit dem Elymat-Verfahren ist an Proben mit unterschiedlicher Dotierungs- und Eisenkonzentration untersucht worden, wobei die Eisenkontamination gezielt entweder mittels “spin-on”-Verfahren oder Ionen-Implantation und einem nachfolgenden Diffusionsschritt erfolgte. Die Modellierung der Messergebnisse ergab eine sehr gute Übereinstimmung zwischen Experiment und Simulation. Erstmals konnten dabei beide Elymat-Messmodi konsistent charakterisiert werden. Speziell konnte der Anstieg der effektiven Lebensdauern mit steigender Laserleistung bei Extraktion des photoinduzierten Diffusionsstroms auf der dem Laser zugewandten Scheibenoberfläche auf einen zunehmenden Driftstromanteil zurückgeführt werden. Die Einfangkoeffizienten der bei Eisenkontamination existierenden relevanten Energieniveaus wurden dabei nicht angepasst sondern unabhängig an Hand von in der Literatur veröffentlichten Messdaten ermittelt. Bei Berücksichtigung beider Zustände des Eisen-Bor-Paares und des Energieniveaus von interstitiellem Eisen können alle in der Literatur veröffentlichten und die hier gewonnenen Ergebnisse mit dem ermittelten Koeffizientensatz korrekt modelliert werden. Bei ausschließlicher Kontamination mit Eisen kann daher die Eisenkonzentration bei Anwendung der elektrostatischen Passivierung mit dem Elymat-Verfahren genau bestimmt werden. Weiterhin ist es in dieser Arbeit erstmals gelungen, mit dem modifizierten Elymat-Verfahren quantitativ die Grenzflächenzustandsdichte D_it und die Isolatorvolumenladung Q_Is von Isolator/Silicium-Strukturen zu bestimmen. Die dazu vorgestellten Auswerteverfahren beruhen auf einer hier entwickelten, physikalisch begründeten Modellierung der Ladungsträgerrekombination an Grenzflächenzuständen bei beleuchteten Elektrolyt/Isolator/Silicium-Strukturen. Die Modellierung erlaubt es, die beim modifizierten Elymat-Verfahren gemessene Abhängigkeit des photoinduzierten Diffusionsstroms von der Grenzflächenrekombination über den gesamten Injektionsbereich des Messgerätes mit sehr guter Übereinstimmung zu beschreiben. Dies ist durch Messungen an einer Vielzahl von thermisch oxidierten Siliciumproben mit unterschiedlichen Oxiddicken bzw. nachfolgenden Temperschritten gezeigt worden. An Hand der Ergebnisse konnten dabei optimierte Messbedingungen für das modifizierte Elymat-Verfahren bestimmt werden. Für die Empfindlichkeit des modifizierten Elymat-Verfahrens hinsichtlich der Bestimmung der Grenzflächenzustandsdichte kann für Proben mit hoher Volumenlebensdauer ein Wert von ca. 1-5*10^9 cm^-2eV^-1 abgeschätzt werden. Die mit dem modifizierten Elymat-Verfahren ermittelten Werte für D_it und Q_Is stimmen sehr gut mit Messergebnissen von etablierten Messverfahren (Konduktanz- bzw. Kapazitäts-Spannungs-Verfahren) an Vergleichsproben überein. Die für die quantitative Bestimmung von D_it und Q_Is benötigten Werte für die Parameter der physikalischen Modellierung konnten ebenfalls experimentell bestimmt bzw. verifiziert werden. Somit konnte in dieser Arbeit gezeigt werden, dass das modifizierte Elymat-Verfahren sehr gut für die exakte und schnelle Prozesskontrolle von Oxidationsprozessen geeignet ist.The subject of this thesis is the detailed investigation of injection level dependent photocurrent measurements. By using the conventional Elymat method the injection level dependence of carrier lifetimes for iron contaminated boron doped silicon samples was determined experimentally and verified by 2D simulations. Obtained results are of fundamental importance for the injection level dependent characterization of insulator/silicon structures with a modified Elymat method which was also carried out. Sufficient passivation of the semiconductor surface is crucial for the correct determination of low level injection lifetimes. In this context it could be shown that the efficiency of the surface passivation with diluted hydrofluoric acid as it is used in the conventional Elymat method is not sufficient. However, the use of electrostatic passivation with the modified Elymat method allows a correct lifetime determination for all injection levels. At low injection this passivation can be applied even with natural oxide as insulator. Lifetime spectroscopy for iron contaminated silicon samples was conducted for samples with different doping and iron concentrations. The contamination with iron was performed using either the spin-on technique or ion implantation, both followed by a thermal drive-in process. A very good agreement between experimental and simulated lifetimes could be achieved. For the first time both Elymat measurement modes could be consistently characterized. In particular, the increase of the effective lifetime with increasing laser power - which is observed when extracting the photo induced diffusion current at the laser facing surface - could be attributed to an increasing drift current. The capture coefficients of the relevant iron energy levels were not fitted but independently determined using previously published lifetime data. Both, published lifetime data and the measured lifetimes of this work could be modeled accurately with the obtained set of capture coefficients when both energy levels of the iron boron pair and the energy level of interstitial iron are accounted for. For samples exclusively contaminated with iron the Elymat method with electrostatic passivation can be used for a precise determination of the iron concentration. Furthermore it is demonstrated for the first time that the modified Elymat method enables the quantitative determination of interface state density D_it and insulator volume charge Q_Is of insulator/silicon structures. The required evaluation procedures are based on a physical model for charge carrier recombination at interface states of illuminated electrolyte/insulator/silicon structures which has been developed within this work. Using this model, the dependence of the photo induced diffusion current on the interface recombination as it is measured with the modified Elymat method can be simulated with very good agreement for the whole investigated injection regime. This has been shown for a lot of thermally oxidized silicon samples with various oxide thicknesses or post oxidation treatments. By means of these results optimized measurement conditions for the modified Elymat method could be defined. The sensitivity of the modified Elymat method for the determination of interface state density could be estimated to be in the range of about 1-5*10^9 cm^-2eV^-1 for samples with high carrier lifetimes. Values of D_it and Q_Is as determined with the modified Elymat method are in very good agreement with values as obtained with established measurement methods (i.e., conductance method and capacitance voltage method, respectively) using comparable samples. To enable quantitative determination of D_it and Q_Is values for the parameters of the physical modeling have to be known. These values could be either obtained or verified experimentally. Consequently in this work it could be shown that the modified Elymat method is very well suited for the accurate and fast control of oxidation processes