Cyclopentasilane (CPS) has been studied as an liquid precursor for the deposition of thin silicon films for printed electronics and related applications. The processing involves a UV‐induced prepolymerization of CPS followed by liquid deposition and low‐temperature thermolysis. An insight into the oligomer and polymer formation including crosslinking in solution using 29 Si NMR spectroscopy and electron spin resonance spectroscopy is reported. Formation of SiH (T‐units) and SiH 3 (M‐units) is observed as well as short‐lived paramagnetic species. Additionally, the polymerization is followed by Raman spectroscopy. Reactive molecular dynamics simulations are applied to develop a theoretical model for the CPS‐ring‐opening and crosslinking steps. The experimental and computational data correspond well to each other and allow insight into the mechanism of polymer formation. The processing steps include spin‐coating, thermal drying, and conversion to amorphous silicon, H‐passivation, and fabrication of a CPS‐derived thin‐film transistor (TFT), without intermediate silicon crystallization. Further improvement is gained by using tetralene as a solvent, leading to a reduction of the time‐consuming polymerization step by one order of magnitude compared to cyclooctane. The overall quality and characteristics of the CPS‐derived spin‐coated silicon thin films correspond to standard plasma enhanced chemical vapor deposition‐derived devices with respect to performance levels.

An advanced and highly scalable approach for determining the number of layers of two-dimensional (2D) materials via optical spectroscopy is introduced. Based on appropriate subjacent layer stacks, the reflectance spectra of the 2D material assemblies exhibit wavelength shifts in distinct minima, which are linearly related to the number of layers. A linear correlation enables straightforward data interpretation, which is essential for implementing simple and comparatively fast measurement routines for process control on wafer scale. The structure of the optical layer stacks as well as the complex refractive indices of 2D materials were found to strongly influence the spectral position of the reflectance minima as well as the magnitude and the linearity of the wavelength shifts. We experimentally prove this method to be applicable for large-area layer counting of subsequently stacked chemical vapor deposition graphene films on a layer stack consisting of silicon nitride and silicon oxide. The measurement results confirm the calculated wavelength shift of the reflection minimum around 540 nm equaling approx. 3 nm per layer. Numerical analysis shows that comparable behavior is also achievable by the tailored design of subjacent layer stacks for graphene oxide, hexagonal boron nitride, and more complex 2D materials like transition-metal dichalcogenides. For the achievement of linear relations between wavelength shifts of the respective minimum and the layer count of the 2D material, analytical design rules are derived considering the optical properties of the underlying layer stack as well as oscillator frequencies within the complex refractive index of the 2D material. The largest signal response of 12 nm per layer was calculated for MoSe2 on an optimized layer stack.

A comparison between self-aligned process (using lift-off) and Ni-SALICIDE used in fabrication of ohmic contacts for SiC Power MOSFET is done. Both processes are demonstrated for 3.3 kV SiC VDMOS transistors fabricated on 100 mm substrates. It is shown that the Ni-SALICIDE process with first silicidation at 500 °C does not degrade the electrical properties of silicon dioxide; particularly, a degradation of the interlayer dielectric between source and gate is not evident. Additionally, this first silicidation is found to have a positive impact on the specific resistance of contacts formed on p-type SiC using NiAl2.6% as an ohmic metal.

In this work, a lateral 4H-SiC n-LDMOS transistor, based on the principle of a reduced surface field due to charge compensation, is investigated by numerical simulations, in order to find adequate fabrication parameters for a lightly doped p-type epitaxy in combination with a higher doped channel region. The purpose of this work is the integration into an existing technology for a 10 V 4H-SiC-CMOS process. The simulations predict in a blocking voltage of 1.3 kV in combination with an On-resistance of 17 mΩcm2 for a device with a RESURF structure with a total implanted Al concentration of 6∙1016 cm-3 and a depth of 1 μm, a field plate of 5 μm and a drift region of 20 μm. The threshold voltage varies from 5 V to 10 V, depending on the thickness of the gate oxide (50 nm to 100 nm).

In this work, monolithically integrated wavelength-selective 4H-SiC UV-sensor arrays were manufactured using two photolithography masks and only one implantation sequence demonstrating the potential of the advanced 4H-SiC process technology for the first time. The process technology is described in detail for the fabrication of a 2 x 2 wavelength-sensitive UV-sensor array including two variants with different thicknesses of the p-emitter. The maximum spectral responsivity is 92 mA/W for a wavelength of 300 nm and the devices with a thick p-emitter and 162 mA/W for a wavelength of 290 nm and devices with the thin p-emitter. The corresponding values of the external quantum efficiency are 38%, and 69%, respectively. Furthermore, another UV-sensor characteristic is found evaluating the current difference between both types with a maximum spectral responsivity of 80.2 mA/W at a wavelength of 270 nm.

In this paper we report on the performance of 4H-SiC bipolar diodes as temperature sensors far beyond 273K. The sensor is measured from 150K to 445K covering a temperature range of 295K. In this operating temperature range, the sensor characteristic VD-T is highly linear and it is dominated by the typical dependence of the p-i-n diode voltage on the temperature. The sensor sensitivity is -4.48mV/K for a diode current of 2nA with a maximum error of 4.3K across the full temperature range. Although 4H-SiC p-i-n are mainly focused on very high temperature applications, our analysis on the performance of bipolar diodes at low temperatures highlights its feasibility as temperature sensor for aerospace and high altitude applications where cryogenic temperatures are achieved.

In this work, the impact of a shallow aluminum channel implantation on the channel properties of SiC p-MOSFETs and digital SiC CMOS devices is investigated. For this purpose, p-MOSFETs, CMOS inverters and ring oscillators with different channel implantation doses were fabricated and electrically characterized. The threshold voltage of the resulting p-MOSFETs was shifted from-5 V to-3.6 V whereas the effective channel mobility was slightly decreased from 11.8 cm2/Vs to 10.2 cm2/Vs for a p-MOSFET channel implantation dose of 2∙10 13 cm -2 compared to the non-implanted channel. The resulting p-MOSFETs enable SiC CMOS logic circuits to operate with a 5 V power supply and to satisfy 5 V TTL input level specification over the whole temperature range of 25°C to 400°C. Furthermore the propagation delay time of inverters was reduced by 80% at 25°C and 40% at 400°C compared to inverters without p-MOSFET channel implantation.

Aluminum implanted 4H-SiC often shows an unexpected increase of the free hole density at elevated temperatures in Hall Effect measurements. Here we show that this phenomenon cannot solely be traced down to the Hall scattering factor and the presence of excited acceptor states. It is necessary to assume an additional defect center in the lower half of the band gap with ionization energies higher than that of aluminum to explain this behavior. Therefore, we investigated ion-implanted square van-der-Pauw samples with Hall Effect and complementary SIMS measurements. An analysis of the data using the neutrality equation reveals compensation ratios of 20 % to 90 %, depending on the aluminum concentration and the concentration of the deep defect center of up to 50 % of the doping.

This paper presents a new type of a polymer bonded soft magnetic material (PBSMM) which can be used to create complex magnetic core geometries. The PBSMM consists of two separate materials, manganese zinc ferrite powder and polydimethylsiloxane (PDMS) as matrix material. The magnetic core losses of the PBSMM where analyzed at 10 kHz and 1 MHz with self-fabricated toroidal core samples by using a custom-made measurement setup in accordance with the IEC-62044-3 norm. The complex permeability was determined by evaluating impedance analyzer measurements between 10 kHz and 1 MHz. It is pointed out that the investigated material can be used for power electronic filter applications and opens the opportunity to create geometrical complex inductive components.

In this work, deep defects in an aluminum-implanted 4H-SiC n-type epitaxy are discussed in dependence on following influencing factors: concentration of implanted aluminum, implantation energy, implantation at 500°C and at room temperature, as well as ascending or descending order of implantation energies during ion implantation using Gaussian profiles. The compensation ratio, which reaches values up to 90% of the implanted aluminum concentration, is determined by Hall Effect measurements. Compensating defect centers (Z 1/2 -, ON x -defects) are detected by Deep Level Transient Spectroscopy after high energy ion implantation using an energy filter, followed by an annealing and an oxidation process.

In this study, the influence of the gate-source voltage on the forward conduction properties of the body-diode in SiC-MOSFETs is demonstrated experimentally and analyzed by numerical simulations. Thereby, it can be figured out that the conduction properties of the body-diode strongly depend on the operational state of the MOS-capacitor. In depletion case, the current via the body-diode is dominant, whereby in accumulation and inversion mode the current mainly flows through the MOS-channel.

Point of load (PoL) converters are emerging as common solution for industrial applications, telecommunications, server, and aerospace. In this work, a topology is designed for a single stage 48 V to 1 V PoL converter by using new gallium nitride (GaN) devices and integrated silicon capacitors. Various wafer-level packaging concepts such as die-to-wafer bonding, wafer-level thinning, and through-silicon via (TSV) will be presented and discussed based on this topology. Furthermore, two novel devices will be developed and used for the packaging concepts. One is a GaN transistor with vertical channel, which will exhibit significantly lower power losses when switching and converting power. The other is an integrated silicon capacitor with lateral geometry, in which positive and negative electrodes are insulated from the substrate and formed on the same side. Simulation is performed to compare the parasitic inductance from the different concepts. A direct bonding process is shown to provide flexibility in engineering new device geometries and can be exploited to mitigate the electrical parasitics.

We demonstrate the applicability of a planar waveguide Bragg grating in cyclo-olefin copolymer (COC) for refractive index sensing. The polymer planar waveguide Bragg grating fabricated using a single writing step technique is coated with a high-index layer of titanium dioxide (TiO2) leading to a distinct birefringence. This in turn results in the splitting of the Bragg reflection into two distinct Bragg wavelengths, which strongly differ regarding their refractive index sensitivities. Where one wavelength is only slightly affected by the ambient refractive index, the second Bragg peak shows a strong sensitivity. Furthermore, we investigate the temperature behaviour of the functionalized sensor and discuss it with respect to applications in refractive index sensing.

Schottky diodes fabricated on free-standing B doped monocrystalline diamond substrate have been investigated. As expected, reverse leakage current due to Schottky barrier lowering has been observed due to the high electric field at the metal-semiconductor interface. Forward current is highest under operating temperatures between 400 and 450K due to incomplete ionization hole mobility dependence on temperature. It is demonstrated that the static device characteristics in the temperature range from 300K to 450K can be modelled by parametrizing an analytical introduced for unipolar SiC and Si diodes.

The development of bipolar 4H-SiC devices for high blocking voltages requires the growth of high carrier lifetime epitaxial layers with low Z 1/2 concentrations. This paper shows a comprehensive investigation of the influence of epitaxial growth parameters (C/Si ratio and growth temperature) on Z 1/2 concentration and minority carrier lifetime. On the basis of a discovered exponential correlation of Z 1/2 with the C/Si ratio and growth temperature, a competitive low Z 1/2 concentration of 1.9∙10 12 cm -3 could be achieved by lowering the growth temperature and switching to higher C/Si ratio. Thermodynamic considerations by an Arrhenius approach reveal a dependency of the formation enthalpy of Z 1/2 on the thermal process and process conditions of the epitaxial growth. Furthermore, the correlation between Z 1/2 and the effective minority carrier lifetime confirms the occurrence of a necessary second recombination mechanism beside the common recombination at deep levels by Shockley-Read-Hall for low Z 1/2 concentration.

Commercial polymer electrolyte membrane (PEM) fuel cell systems require pure hydrogen feed gas (ISO 14687-2), otherwise impurities and inert gases would accumulate. Inert gases are difficult to remove, but do not hazard the fuel cell stack itself. Therefore, two purge strategies are introduced and experimentally investigated which enable fuel cell operation with up to 30 vol.% nitrogen content in the feed gas. Both strategies use a commercial on-line hydrogen sensor at the stack outlet either to trigger a discontinuous purge or to control the purge valve continuously. The experimental results show that the discontinuous purge strategy can be applied up to 10 vol.% nitrogen content in the feed gas. The continuous purge strategy was successfully operated with up to 30 vol.% nitrogen content and achieved the theoretical maximum fuel efficiency between 80 and 100%. The influence of nitrogen crossover on fuel efficiency and operating performance was investigated and found negligible. To sum up, the new continuous purge strategy offers an efficient, easy-to-implement, and robust solution to operate polymer electrolyte membrane fuel cell systems with up to 30 vol.% nitrogen content in the feed gas.

In this study, a first detailed comparison of the spectral responsivity and internal quantum efficiency (IQE) of 4H-SiC UV sensors with ion implanted and epitaxially grown p-emitter is presented. Additionally, an analytical device model is implemented. It is evident that radiation damage and defects produced during the ion implantation and subsequent annealing are mainly responsible for the approximately 10% lower IQE for wavelengths smaller than 280 nm. In the device model, these defects correspond to a lower effective minority carrier diffusion length within the p(+)-emitter for the ion implanted devices. Nevertheless, both emitter technologies are suitable in order to achieve a high sensor performance (peak IQE > 60%).

In this study, the influence of the emitter efficiency on the forward current-voltage characteristics, especially the conductivity modulation of bipolar SiC-diodes was analyzed. It was determined that the emitter efficiency of p-emitters formed by ion implantation is significantly lower compared to p-emitters formed by epitaxy. In contrast to comparable studies, experimental approach was arranged that the influence of the quality of the drift-layer or the thickness of the emitter on the conductivity modulation could be excluded for the fabricated bipolar SiC-diodes of this work. Thus, it can be established that the lower emitter injection efficiency is mainly caused by the reduced electron lifetime in p-emitters formed by ion implantation. Therefore, a significant enhancement of the electron lifetime in implanted p-emitters is mandatory for e.g. SiC-MPS-diodes where the functionality of the devices depends significantly on the injection efficiency.

The growth of silver shells on gold nanorods is investigated by in situ liquid cell transmission electron microscopy using an advanced liquid cell architecture. The design is based on microwells in which the liquid is confined between a thin Si3N4 membrane on one side and a few-layer graphene cap on the other side. A well-defined specimen thickness and an ultraflat cell top allow for the application of high-resolution TEM and the application of analytical TEM techniques on the same sample. The combination of high-resolution data with chemical information is validated by radically new insights into the growth of silver shells on cetrimonium bromide stabilized gold nanorods. It is shown that silver bromide particles already formed in the stock solution play an important role in the exchange of silver ions. The Ag shell growth can be directly correlated with the layer-by-layer dissolution of AgBr nanocrystals, which can be controlled by the electron flux density via distinctly generated chemical species in the solvent. The derived model framework is confirmed by in situ UV-vis absorption spectroscopy evaluating the blue shift in the longitudinal surface plasmon resonance of anisotropic NRs in a complementary batch experiment.