CiS Forschungsinstitut für Mikrosensorik GmbH

An approach to evaluate the microwave-detected photoconductance decay (MWPCD) is developed, which allows to extract the minority carrier lifetime as a function of the excess carrier density from a single MWPCD measurement. The method is shown to be applicable to thin (w≲200 μm) silicon wafers with low minority carrier recombination at the surfaces and bulk lifetimes in the range of about 1–100 μs. Comparison of the MWPCD results with minority carrier lifetime measurements using the quasi-steady-state photoconductance method reveals very good agreement between both types of measurement. Only when the photoconductance exceeds 30% of the dark conductivity, is a deviation observed, because then the MWPCD signal is no longer directly proportional to the excess carrier density. Minority carrier trapping is found to affect the MWPCD signal only in the tail of the measured photoconductance decay. The evaluation method is used to map the interstitial iron content with high spatial resolution, as well as to determine the minority carrier trap density. An excellent agreement between numerical simulation and measured MWPCD signal is found revealing the assumptions made for the evaluation approach to be valid. This evaluation of the MWPCD measurement is well suited to characterize silicon of low purity and low crystalline quality, which is often employed to solar cells with high spatial resolution.

Cardiovascular diseases are among the most common causes of death in industrial countries. In order to take preventive actions, it is of great interest, to both physicians and patients, to determine cardiovascular risk factors early. To address this problem, a wearable in-ear measuring system (IN-MONIT) for 24/7 monitoring of vital parameters has been developed. The central component is a microoptic reflective sensor located inside the auditory canal. From the measured photoplethysmographic curves, heart activity and heart rate can be derived. In this paper, we describe the optoelectronic sensor concept and the autonomous design of the IN-MONIT measurement system. For the assessment of heart rate, different algorithms are introduced and the performance of the developed sensor system is evaluated in relation to conventional systems. In addition, the robustness to external artifacts is evaluated and artifact reduction strategies are considered.

Excess-carrier recombination lifetime is a key parameter in silicon solar cell design and production. With the vast international use and recent standardization (SEMI PV13) of eddy-current wafer and brick silicon lifetime test instruments, it is important to quantify the inter- and intralaboratory repeatability. This paper presents the results of an international interlaboratory study conducted with 24 participants to determine the precision of the SEMI PV13 eddy-current carrier lifetime measurement test method. Overall, the carrier recombination lifetime between-laboratory reproducibility was found to be within ±11% for the quasi-steady-state mode and ±8% for transient mode for wafer samples, and within ±4% for bulk samples.

The power supply of wireless sensor systems is an issue of growing importance since replacement of batteries is very expensive over the sensor lifetime. An energy harvesting system which generates electrical energy from flowing media without any rotating parts will be presented. The harvester consists of piezoelectric cantilevers which oscillate in a media flow and convert kinetically energy into electrical energy. A model of the harvester was developed and the influence of geometrical parameters was simulated. Important design information was achieved as result of the simulation. Several harvester systems were built up using commercially available and not optimized PZT ceramic plates. Measurements were carried out in wind and water channels. It was found that the output voltage of the harvesters increase with the streaming velocity of the media. An output power of about 0.1mW was achieved at power adjustment in air. Optimized harvesters could deliver an up to two orders higher output.

We prepared Si(100) surfaces with anomalous atomic double-layer steps grown via chemical vapor deposition. Scanning tunneling microscopy resolved ${D}_{A}$-type steps, supported by low-energy electron diffraction, Fourier-transform infrared spectroscopy, and in situ reflection anisotropy spectroscopy, which enabled direct control of majority domain formation. We attribute the energetically unfavorable step structure to interaction of the surface with the H${}_{2}$ ambient, driving a dynamic step formation process governed by surface vacancy generation, diffusion, and annihilation at step edges.

Abstract Light‐induced degradation of charge carrier lifetime was observed in indium‐doped silicon. After defect formation, an annealing step at 200 °C for 10 min deactivates the defect and the initial charge carrier lifetime is fully recovered. The observed time range of the defect kinetics is similar to the well known defect kinetics of the light‐induced degradation in boron‐doped samples. Differences between defect formation in boron‐ and indium‐doped silicon are detected and discussed. A new model based on an acceptor self‐interstitial A Si –Si i defect is proposed and established with experimental findings and existing ab‐initio simulations. magnified image Charge carrier lifetime degradation during light soaking of indium‐doped samples with different oxygen concentrations. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The application of an Isopropanol IPA free potassium hydroxide KOH solution was evaluated in order to prepare random pyramids on as cut crystalline n type Si wafers to reduce reflection losses of substrates for high efficiency hetero junction solar cells. The influence of saw damage removal and texturization processes on the resulting pyramid morphology and the corresponding interplay between optical and electronic properties are revealed. It is shown that both the depth of the saw damage etching SDE and the duration of the texturization etching have crucial influence on the resulting pyramid size distribution. Reflection losses can be reduced with decreasing fraction of small pyramids. By intermediate saw damage removal and texture etching times in IPA free KOH solution the densities of electronic interface states were found to be strongly decreased Dit,min lt; 5 E 11 cm 2eV 1 , in comparison to pyramids prepared in IPA containing solutions. For the purpose of fabricating amorphous crystalline a Si H c Si heterojunction solar cells the Si substrate surfaces were passivated with an intrinsic layer of amorphous silicon a Si H i leading to minority charge carrier lifetimes taueff of 2 to 4 ms, depending on the preceding texturization process.

The charge dynamics and the interface defect state density of AlOx SiNx passivation stacks deposited by plasma enhanced chemical vapor deposition PECVD on crystalline silicon c Si wafers are investigated. High frequency 1 MHz capacitance voltage C V measurements were performed on stacks in the as deposited state and after an annealing step. C V sweeps reveal an initially high negative charge density for the as deposited sample, activated by the thermal budget during SiNx deposition. However, this charge state is unstable and reduced owning to electron detrapping and emission into the c Si upon applying moderate voltages. In the annealed sample, the AlOx SiNx stack has a stable negative fixed charge. Both for as deposited and for annealed samples, applying a positive or negative constant gate voltage stress Vstress enhances or reduces the negative effective charge density Qox,eff , respectively. Injection of charges from the c Si into traps in the AlOx SiNx stack is identified as the mechanism responsible for this behavior. We conclude that in addition to fixed negative charges trapping of negative charges near the interface is a crucial mechanism contributing to the total effective negative charge of the stack. Their contribution depends on the temperature and duration of the thermal treatment. Additionally, a large Vstress leads to generation of additional Si dangling bond defects over the entire c Si bang gap at the c Si AlOx interface

We study the initial interaction of adsorbed H2O with P-rich and Ga-rich GaP(100) surfaces. Atomically well defined surfaces are prepared by metal-organic vapour phase epitaxy and transferred contamination-free to ultra-high vacuum, where water is adsorbed at room temperature. Finally, the surfaces are annealed in vapour phase ambient. During all steps, the impact on the surface properties is monitored with in situ reflection anisotropy spectroscopy (RAS). Photoelectron spectroscopy and low-energy electron diffraction are applied for further in system studies. After exposure up to saturation of the RA spectra, the Ga-rich (2 × 4) surface reconstruction exhibits a sub-monolayer coverage in form of a mixture of molecularly and dissociatively adsorbed water. For the p(2 × 2)/c(4 × 2) P-rich surface reconstruction, a new c(2 × 2) superstructure forms upon adsorption and the uptake of adsorbate is significantly reduced when compared to the Ga-rich surface. Our findings show that microscopic surface reconstructions of GaP(100) greatly impact the mechanism of initial interface formation with water, which could benefit the design of e.g. photoelectrochemical water splitting devices.

In this work SiNX deposited on silicon was locally ablated using laser irradiation. The focus was set on the investigation of the ablation mechanisms where a picosecond (ps) pulse laser is used with three wavelengths 1064, 532, 355 nm. The ablated areas were characterized by light microscopy and the threshold fluences were determined for various layer thicknesses. Furthermore, four-probe sheet-resistance and SunsVoc measurements were conducted. Light microscopy images were taken and compared to simulated color maps, which were calculated from spectral reflection coefficients. The results of sheet resistance and SunsVoc measurements show an influence on the underlying silicon for all three wavelengths used. However, light microscopy images reveal for the first time a change from indirect ablation (lift-off) to partial lift-off for a thin a-SiNx:H-layer (n ≈ 2.1, t ≈ 75 nm) by using a VIS picosecond laser. Thus, a first step towards selective laser ablation was made of dielectrics.

Abstract In this study we focus on optimizing the passivation of pyramid textured n type crystalline silicon c Si wafers by deposition of intrinsic amorphous Si a Si H i layers. By tatistical analysis of the pyramid size distribution it is revealed that a decreased fraction of small pyramids leads to longer minority charge carrier lifetimes and, thus, a higher Voc potential for solar cells. Further, we demonstrate that optimized parameters for the deposition of a Si H i layers on planar Si 111 wafers can be transferred to the a Si H deposition on random pyramid textured Si 100 wafers exhibiting facets with 111 orientation. In particular the influence of the deposition temperature on the optical layer properties is elucidated. Furthermore, the favorable impact of post deposition plasma hydrogenation and annealing on the charge carrier lifetime gt; 5 ms and the implied open circuit voltage up to 738 mV are demonstrated

Double-layer step formation on Si(100) substrates is a crucial prerequisite for antiphase-domain free III–V compound semiconductor heteroepitaxy. Due to its unequaled relevance in microelectronics, the (100) oriented surface of silicon is by far the most studied semiconductor surface. However, Si(100) preparation in hydrogen process gas ambient, which is commonly employed for Si and III–V device preparation, is completely different from preparation in ultra-high vacuum due to strong interaction between H _2 and the Si surface, leading to a kinetically driven different step formation. Here, we observe chemical layer-by-layer removal of surface atoms from the terraces at the Si(100) surface during annealing in hydrogen ambient. Mutually perpendicularly oriented dimers on subsequently removed monolayers induce oscillations in the in situ reflection anisotropy spectroscopy (RAS) signal. Scanning tunneling microscopy measurements support a model, where surface atom removal proceeds by formation and anisotropic expansion of vacancy islands on the terraces. We determined an activation energy E _d of 2.75 ± 0.20 eV for Si etching in H _2 ambient by transient in situ RAS measurements. In situ control of the highly reactive Si(100) surface preparation is essential for subsequent defect-free III–V heteroepitaxy.

A detailed knowledge of the electronic properties of individual dislocations is necessary for next generation nanodevices. Dislocations are fundamental crystal defects controlling the growth of different nanostructures (nanowires) or appear during device processing. We present a method to record electric properties of single dislocations in thin silicon layers. Results of measurements on single screw dislocations are shown for the first time. Assuming a cross-section area of the dislocation core of about 1 nm2, the current density through a single dislocation is J = 3.8 × 1012 A/cm2 corresponding to a resistivity of ρ ≅ 1 × 10−8 Ω cm. This is about eight orders of magnitude lower than the surrounding silicon matrix. The reason of the supermetallic behavior is the high strain in the cores of the dissociated dislocations modifying the local band structure resulting in high conductive carrier channels along defect cores.

Pattern Transfer Printing (PTPTM) is a patented novel non-contact printing technology developed and commercialized by Utilight for advanced front side metallization of c-Si PV solar cells. As PTPTM is based on laser induced deposition from a polymer substrate, the geometry of the printed features is not restricted by the characteristics of a printing screen, allowing for much finer, higher and uniform fingers. We present the results achieved by printing the front side finger lines and bus bars of mono- and multi-crystalline solar cells with PTPTM technology and compare these with results of neighboring cells manufactured by state-of-the-art screen printing technology. Finger lines with high aspect ratio and uniform line shape down to 20 μm width could be printed. Solar cells with 29 μm wide double printed PTP finger lines show an efficiency increase of up to 0.4%abs.

In Europe, the FLUXONICS Foundry develops fabrication processes and design kits for superconductor digital and mixed-signal circuits. We describe the implementation of the “European Roadmap for Superconductor Electronics” into the recent foundry process for superconductor digital electronics. Following the hierarchical cell-based design strategy, we developed a design kit with basic cells. We present experimental results of the process quality, the verified operation margins of the library cells, and the results of low- and high-speed investigations of test circuits. The process is suitable for the integration of complex digital and mixed-signal circuits for smart multichannel superconductor sensor applications with a digital interface.

Carrier mobilities and concentrations were measured for different p- and n-type silicon materials in the temperature range 0.3–300 K. Simulations show that experimentally determined carrier mobilities are best described in this temperature range by Klaassen’s model. Freeze-out reduces the carrier concentration with decreasing temperature. Freeze-out, however, depends on the dopant type and initial concentration. Semi-classical calculations are useful only for temperatures above 100 K. Otherwise quantum mechanical calculations are required.

Cardiovascular diseases are among the most common causes of death in western industrial nations. It is of great interest of both physician and patient to determine the cardiovascular risk factors early in order to take preventive measures. To assist the recognition of irregularities in a subject's cardiovascular system, we develop an optic 24/7 inear monitoring system (IN-MONIT). The central component is a micro-optic remission/reflection sensor (MORES), which is placed inside the auditory canal. There the pulsation of blood within the capillaries is measured by means of optical absorption. From the resulting photoplethysmographic curves (pulse plethysmogram, PPG), the heart rate, oxygen saturation (SpO2), respiratory rate and higher order moments can be derived. The optical absorption data are processed locally using a microcontroller and the results are transferred wirelessly to a personal digital assistant (PDA) or PC for sophisticated classification. This paper introduces the IN-MONIT system and two algorithms for heart rate determination from ECG or PPG data. The performance of these algorithms was tested using annotated ECG data from the "MIT-BIH Normal Sinus Rhythm Database", synchronously recorded ECG and pulse oximeter data, and data acquired by the MORES sensor.

Superconductor electronics offers logic circuits for high-speed data processing and high-performance computing. The main barrier to practical application is the lack of high-speed and low-power memory. It is widely believed that the most reliable and functional bit cell for superconducting memory is the vortex transitional bit cell, which was successfully used by Nagasawa in a 4-kb memory. This paper reviews existing challenges in this type of Josephson memory devices and discusses engineering issues in implementing a model single flux quantum random access memory. We evaluate the contributions that various components of the memory system make to delay and power dissipation. The 256-bit memory provides an experimentally confirmed read access time of 190 ps. As a result, we found that delay and power dissipation are found largely in the address decoder, line drivers, bit-selection scheme, and the data readout circuitry. With these circuits being similar for various magnetic memory devices, our findings provide essential data for a comprehensive assessment of new concepts for bit cells, readout, and write in superconducting memories.

A capacitive switching behavior is observed in a Si 3 N 4 /p‐Si‐based metal–insulator–semiconductor (MIS) structure due to the electron tunneling at the Si 3 N 4 /p‐Si interface. A BiFeO 3 (BFO) layer is deposited on Si 3 N 4 /p‐Si by pulsed laser deposition technique to obtain the memcapacitive effect as the distribution of positive charges in the Si 3 N 4 layer can be stabilized by the polarization charge of the ferroelectric BFO coating layer. The capacitive switching behavior of the Al/BFO/Si 3 N 4 /p‐Si/Au MIS structure is also sensitive to both intensity and wavelength of the illumination, which offers the possibility to create a photodetector for both intensity and color detection. Thus, the presented device has the potential application for future information storage and visible light communications. As an example, a photocapacitive demodulator with capability of decoding both wavelength and intensity information of the incident light is demonstrated.

We herein propose the quantum-flux-latch (QFL) as a novel latch for adiabatic quantum-flux-parametron (AQFP) logic. A QFL is very compact and compatible with AQFP logic gates and can be read out in one clock cycle. Simulation results revealed that the QFL operates at 5 GHz with wide parameter margins of more than ±22%. The calculated energy dissipation was only ∼0.1 aJ/bit, which yields a small energy delay product of 20 aJ·ps. We also designed shift registers using QFLs to demonstrate more complex circuits with QFLs. Finally, we experimentally demonstrated correct operations of the QFL and a 1-bit shift register (a D flip-flop).