The ASi-Sii defect model of light-induced degradation (LID) in silicon: a discussion and review. - In: Physica status solidi, ISSN 1862-6319, Bd. 219 (2022), 19, 2200099, S. 1-10
The ASi-Sii defect model as one possible explanation for light-induced degradation (LID) in typically boron-doped silicon solar cells, detectors, and related systems is discussed and reviewed. Starting from the basic experiments which led to the ASi-Sii defect model, the ASi-Sii defect model (A: boron, or indium) is explained and contrasted to the assumption of a fast-diffusing so-called “boron interstitial.” An LID cycle of illumination and annealing is discussed within the conceptual frame of the ASi-Sii defect model. The dependence of the LID defect density on the interstitial oxygen concentration is explained within the ASi-Sii defect picture. By comparison of electron paramagnetic resonance data and minority carrier lifetime data related to the assumed fast diffusion of the “boron interstitial” and the annihilation of the fast LID component, respectively, the characteristic EPR signal Si-G28 in boron-doped silicon is related to a specific ASi-Sii defect state. Several other LID-related experiments are found to be consistent with an interpretation by an ASi-Sii defect.
https://doi.org/10.1002/pssa.202200099
Emerging smart design of electrodes for micro-supercapacitors: a review. - In: SmartMat, ISSN 2688-819X, Bd. 3 (2022), 3, S. 447-473
Owing to high power density and long cycle life, micro-supercapacitors (MSCs) are regarded as a prevalent energy storage unit for miniaturized electronics in modern life. A major bottleneck is achieving enhanced energy density without sacrificing both power density and cycle life. To this end, designing electrodes in a “smart” way has emerged as an effective strategy to achieve a trade-off between the energy and power densities of MSCs. In the past few years, considerable research efforts have been devoted to exploring new electrode materials for high capacitance, but designing clever configurations for electrodes has rarely been investigated from a structural point of view, which is also important for MSCs within a limited footprint area, in particular. This review article categorizes and arranges these “smart” design strategies of electrodes into three design concepts: layer-by-layer, scaffold-assisted and rolling origami. The corresponding strengths and challenges are comprehensively summarized, and the potential solutions to resolve these challenges are pointed out. Finally, the smart design principle of the electrodes of MSCs and key perspectives for future research in this field are outlined.
https://doi.org/10.1002/smm2.1094
The angle dependent ΔE effect in TiN/AlN/Ni micro cantilevers. - In: Sensors and actuators, ISSN 1873-3069, Bd. 345 (2022), 113784, S. 1-12
In this work, magnetoelectric MEMS sensors based on a TiN/AlN/Ni laminate are investigated for the first time in regards of the anisotropic elastic properties when using hard magnetic Nickel as magnetostrictive layer. The implications of crystalline, uniaxial and shape anisotropy are analysed arising from the anisotropic ΔE effect in differently oriented cantilevers with 25 µm length and 15˚ spacing. The ΔE effect is derived analytically to consider the angular dependency of the different anisotropies within the sensors. In the measured frequency spectra complex profiles are observable consisting of contributions from neighbouring structures which are connected by a common electrode. The crosstalk effect is strongly depending on the cantilever orientation and reflects the anisotropic mechanical properties of the material stack. The intensity of the crosstalk effect is increasing for shortened cantilevers and narrowing distance between structures. The ΔE effect is investigated based on cantilevers of different angular spacing and of a single cantilever that is rotated in the magnetic field. The derived peak sensitivities are reaching values of 1.15 and 1.31T-1. The angular dependency of the sensitivity is found to be approximately constant for differently oriented cantilevers. In contrast, for a singly rotated cantilever an angular dependency of the 4th order is observed.
https://doi.org/10.1016/j.sna.2022.113784
MOCVD surface preparation of V-groove Si for III-V growth. - In: Journal of crystal growth, Bd. 597 (2022), 126843
V-groove nanopatterning of Si substrates has recently demonstrated promise for achieving high-quality III-V-on-Si epitaxy while providing a lower-cost processing route than chemo-mechanical polishing to produce epi-ready planar wafers. A key factor in determining the crystalline quality of III-V buffer layers is the Si surface structure and its chemical composition. Unlike planar Si surfaces, the surfaces of V-grooves prior to growth have not been studied in detail. Here, we study the surface of V-groove Si prepared for GaP nucleation via X-ray photoelectron spectroscopy and low-energy electron diffraction. We identify several pretreatments, using both 830˚C and 1000˚C annealing under an As background pressure, as being suitable for deoxidizing and cleaning the V-groove Si surface. The V-groove Si was found to behave similarly to reference Si(0 0 1) and Si(1 1 1) planar samples, demonstrating that in situ techniques such as reflection anisotropy spectroscopy can be used on reference samples to infer the state of the V-groove surface, and indicating that the extensive research on planar Si surfaces can be directly applied to V-grooves.
https://doi.org/10.1016/j.jcrysgro.2022.126843
Combining advanced photoelectron spectroscopy approaches to analyse deeply buried GaP(As)/Si(100) interfaces : Interfacial chemical states and complete band energy diagrams. - In: Applied surface science, Bd. 605 (2022), 154630
The epitaxial growth of the polar GaP(100) on the nonpolar Si(100) substrate suffers from inevitable defects at the antiphase domain boundaries (APDs), resulting from mono-atomic steps on the Si(100) surface. Stabilization of Si(100) substrate surfaces with As is a promising technological step enabling the preparation of Si substrates with double atomic steps and reduced density of the APDs. In this paper, 4-50-nm-thick GaP epitaxial films were grown on As-terminated Si(100) substrates with different types of doping, miscuts, and As-surface termination by metalorganic vapor phase epitaxy (MOVPE). The GaP(As)/Si(100) heterostructures were investigated by X-ray photoelectron spectroscopy (XPS) combined with gas cluster ion beam (GCIB) sputtering and by hard X-ray photoelectron spectroscopy (HAXPES). We found residuals of As atoms in the GaP lattice (∼0.2-0.3 at.%) and a localization of As atoms at the GaP(As)/Si(100) interface (∼1 at.%). Deconvolution of core level peaks revealed interface core level shifts. In As core levels, chemical shifts between 0.5 and 0.8 eV were measured and identified by angle-resolved XPS measurements. Similar valence band offset (VBO) values of 0.6 eV were obtained, regardless of the doping type of Si substrate, Si substrate miscut or type of As-terminated Si substrate surface. The band alignment diagram of the GaP(As)/Si(1 0 0) heterostructure was deduced.
https://doi.org/10.1016/j.apsusc.2022.154630
Highly efficient passive Tesla valves for microfluidic applications. - In: Microsystems & nanoengineering, ISSN 2055-7434, Bd. 8 (2022), 1, 97, S. 1-12
A multistage optimization method is developed yielding Tesla valves that are efficient even at low flow rates, characteristic, e.g., for almost all microfluidic systems, where passive valves have intrinsic advantages over active ones. We report on optimized structures that show a diodicity of up to 1.8 already at flow rates of 20 μl s^-1 corresponding to a Reynolds number of 36. Centerpiece of the design is a topological optimization based on the finite element method. It is set-up to yield easy-to-fabricate valve structures with a small footprint that can be directly used in microfluidic systems. Our numerical two-dimensional optimization takes into account the finite height of the channel approximately by means of a so-called shallow-channel approximation. Based on the three-dimensionally extruded optimized designs, various test structures were fabricated using standard, widely available microsystem manufacturing techniques. The manufacturing process is described in detail since it can be used for the production of similar cost-effective microfluidic systems. For the experimentally fabricated chips, the efficiency of the different valve designs, i.e., the diodicity defined as the ratio of the measured pressure drops in backward and forward flow directions, respectively, is measured and compared to theoretical predictions obtained from full 3D calculations of the Tesla valves. Good agreement is found. In addition to the direct measurement of the diodicities, the flow profiles in the fabricated test structures are determined using a two-dimensional microscopic particle image velocimetry (μPIV) method. Again, a reasonable good agreement of the measured flow profiles with simulated predictions is observed.
https://doi.org/10.1038/s41378-022-00437-4
Tandem nanostructures: a prospective platform for photoelectrochemical water splitting. - In: Solar RRL, ISSN 2367-198X, Bd. 6 (2022), 9, 2200181, S. 1-33
A platform for efficient photoelectrochemical (PEC) water splitting must fulfil different requirements: the absorption of the solar spectrum should be maximized in use for charge carrier generation. To avoid recombination, fast separation of charge carriers is required and the energetic positions of the band structure(s) must be optimized with respect to the water splitting reactions. In these respects, constructing tandem nanostructures with rationally designed nanostructured units offers a potential opportunity to break the performance bottleneck imposed by the unitary nanostructure. So far, quite a few tandem nanostructures have been designed, fabricated, and employed to improve the efficiency of PEC water splitting, and significant achievements have been realized. This review focuses on the current advances in tandem nanostructures for PEC water splitting. Firstly, the state of the art for tandem nanostructures applied in PEC water splitting is summarized. Secondly, the advances in this field and advantages arising of employing tandem nanostructures for PEC water splitting are outlined. Subsequently, different types of tandem nanostructures are reviewed, including core-shell tandem nanostructured photoelectrode, the two-photoelectrode tandem cell, and the tandem nanostructures of plasmon related devices for PEC water splitting. Based on this, the future perspective of this field is proposed.
https://doi.org/10.1002/solr.202200181
Development of low-gain avalanche detectors in the frame of the acceptor removal phenomenon. - In: Physica status solidi, ISSN 1862-6319, Bd. 219 (2022), 17, 2200177, S. 1-7
Low-gain avalanche detectors (LGAD) suffer from an acceptor removal phenomenon due to irradiation. This acceptor removal phenomenon is investigated in boron, gallium, and indium implanted samples by 4-point-probe (4pp) measurements, low-temperature photoluminescence spectroscopy (LTPL), and secondary ion mass spectrometry (SIMS) before and after irradiation with electrons and protons. Different co-implantation species are evaluated with respect to their ability to reduce the acceptor removal phenomenon. In case of boron, the beneficial effect is found to be most pronounced for the low-dose fluorine and high-dose nitrogen co-implantation. In case of gallium, the low-dose implantations of carbon and oxygen are found to be beneficial. For indium, the different co-implantation species have no beneficial effect. SIMS boron concentration depth profiles measured before and after irradiation show no indication of a fast movement of boron at room temperature. Hence, the discussed BSi-Sii-defect explanation approach of the acceptor removal phenomenon seems to be more likely than the other discussed Bi-Oi-defect explanation approach.
https://doi.org/10.1002/pssa.202200177
Low-temperature photoluminescence investigation of light-induced degradation in boron-doped CZ silicon. - In: Physica status solidi, ISSN 1862-6319, Bd. 219 (2022), 17, 2200180, S. 1-9
Light-induced degradation (LID) in boron-doped Czochralski grown (CZ) silicon is a severe problem for silicon devices such as solar cells or radiation detectors. Herein, boron-doped CZ silicon is investigated by low-temperature photoluminescence (LTPL) spectroscopy. An LID-related photoluminescence peak is already found while analyzing indium-doped p-type silicon samples and is associated with the ASi-Sii defect model. Herein, it is investigated whether a similar peak is present in the spectra of boron-doped p-type CZ silicon samples. The presence of change in the photoluminescence signal intensity due to activation of the boron defect is investigated as well. Numerous measurements on boron-doped samples are made. For this purpose, samples with four different boron doping concentrations are analyzed. The treatments for activation of the boron defect are based on the LID cycle. During an LID cycle, an additional peak or shoulder neither in the areas of the boron-bound exciton transverse acoustic and nonphonon-assisted peaks (BTA, BNP) nor in the area of the boron-bound exciton transverse optical phonon-assisted peak (BTO) is found. The defect formation also does not lead to a lower photoluminescence (PL) intensity ratio BTO(BE)/ITO(FE).
https://doi.org/10.1002/pssa.202200180
Mathematical analysis of a low cost mechanical ventilator respiratory dynamics enhanced by a sensor transducer (ST) based in nanostructures of Anodic Aluminium Oxide (AAO). - In: Mathematics, ISSN 2227-7390, Bd. 10 (2022), 14, 2403, S. 1-32
Mechanical ventilation systems require a device for measuring the air flow provided to a patient in order to monitor and ensure the correct quantity of air proportionated to the patient, this device is the air flow sensor. At the beginning of the COVID-19 pandemic, flow sensors were not available in Peru because of the international supply shortage. In this context, a novel air flow sensor based on an orifice plate and an intelligent transducer was developed to form an integrated device. The proposed design was focused on simple manufacturing requirements for mass production in a developing country. CAD and CAE techniques were used in the design stage, and a mathematical model of the device was proposed and calibrated experimentally for the measured data transduction. The device was tested in its real working conditions and was therefore implemented in a breathing circuit connected to a low-cost mechanical ventilation system. Results indicate that the designed air flow sensor/transducer is a low-cost complete medical device for mechanical ventilators that is able to provide all the ventilation parameters by an equivalent electrical signal to directly display the following factors: air flow, pressure and volume over time. The evaluation of the designed sensor transducer was performed according to sundry transducer parameters such as geometrical parameters, material parameters and adaptive coefficients in the main transduction algorithm; in effect, the variety of the described results were achieved by the faster response time and robustness proportionated by transducers of nanostructures based on Anodic Aluminum Oxide (AAO), which enhanced the designed sensor/transducer (ST) during operation in intricate geographic places, such as the Andes mountains of Peru.
https://doi.org/10.3390/math10142403