Detrmination of the parameters of the ground state of C2H3D molecule

Present study dedicated to analysis of C2H3D molecule spectra and determination of the parameters of the ground vibrational state of the molecule. In total, positions of more than 10000 transitions were determined. 1037 ground state combination differences were used to improve ground state parameters of the molecule

Amorphous and highly nonstoichiometric titania (TiOx) thin films close to metal-like conductivity

Oxygen-deficient titanium oxide films (TiOx) have been prepared by pulsed laser deposition at room temperature. Samples in their as-deposited state have an average composition of TiO1.6, are optically absorbing and show electronic conductivities in the range of 10 S cm−1. The films are metastable and consist of grains of cubic titanium monoxide (γ-TiO) embedded in an amorphous TiO1.77 matrix. Upon annealing in an argon atmosphere the electrical conductivity of the films increases and comes close to metal-like conductivity (1000 S cm−1) at about 450 °C whereas the local structure is changed: nanocrystalline grains of metallic Ti are formed in the amorphous matrix due to an internal solid state disproportionation. The highly conductive state can be frozen by quenching. During heat treatment in an argon atmosphere a stoichiometric rutile TiO2 surface layer forms due to oxidation by residual oxygen. The combination of a highly conductive TiOx film with such an approximately 20 nm thick rutile cover layer leads to a surprisingly high efficiency for the water-splitting reaction without the application of an external potential

Untersuchung von Interdiffusion, elastischer Gitterverzerrung und Relaxation in epitaktischen Si1−x_{1-x}Gex_{x}/Si-Heterostrukturen mit Ionenstreuung

Si/Si$_{1-x}$Ge$_{x}$-heterostructures and -superiattices are favourable candidates for new high-speed electronic and optoelectronic devices based on Si-technology. Due to the large lattice mismatch of 4.2% between Si and Ge, epitaxial growth of heterostructures leads to tetragonal elastic strain of the unit cell. Above the critical layer thickness the structures start to relax by the formation of misfitand threading-dislocations. Thermal annealing, which is frequently required for device fabrication, can result in relaxation and interdiffusion between the individual layers. The dependence of elastic strain and defect densities on layer thickness and growth temperature has been studied in MBE-grown Si/Si$_{1-x}$Ge$_{x}$ - heterostructures using Rutherhord backscattering spectroscopy (RBS), ion channeling, transmission electron microscopy and X-ray diffraction. Defect densities in single layers above critical thicknesses have been obtained from planar dechanneling measurements. Rapid thermal annealing at temperatures above 1000°C was used to improve the crystalline quality and resulted in a decrease of the threading dislocation density of about 70%. Pseudomorphic, fully strained Si$_{.67}$Ge$_{.33}$-layers with thicknesses of 2000 $\mathring{A}$ have been fabricated at a low growth temperature of only 450°C. The minimum yield value of only 3.2% indicates a very low defect density. Angular scans along (100)-planes through [110]-orientations have been performed to obtain a measurement of the tetragonal lattice distortion. Thermal interdiffusion between individual layers has been studied using 5-period channeling, transmission electron microscopy and X-ray diffraction. Defect densities in single layers above critical thicknesses have been obtained from planar dechanneling measurements. Rapid thermal annealing at temperatures above 1000°C was used to improve the crystalline quality and resulted in a decrease of the threading dislocation density of about 70%. Pseudomorphic, fully strained Si$_{.67}$Ge$_{.33}$-layers with thicknesses of 2000 $\mathring{A}$ have been fabricated at a low growth temperature of only 450°C. The minimum yield value of only 3.2% indicates a very low defect density. Angular scans along (100)-planes through [110]-orientations have been performed to obtain a measurement of the tetragonal lattice distortion. Thermal interdiffusion between individual layers has been studied using 5-period Si/Si$_{1-x}$Ge$_{x}$-superlattices with periods of 200 $\mathring{A}$ on both Si (asymmetrically) buffer layers. Interdiffusion coefficients have been obtained from a Fourier analysis of the measured RBS spectra. In both cases the thermal dependence of the interdiffusion coefficients for a fixed Ge concentration, x, follows an Arrhenius law. Inderdiffusion is strongly dependent on the Ge concentration in the Si/Si$_{1-x}$Ge$_{x}$ layers. Medium energy ion scattering (MEIS) using a position sensitive, electrostatic analyser was employed to investigate very thin Si/Ge-superlattices with layer thicknesses below 40 $\mathring{A}$. The relative energy resolution of 4x10$^{-3}$ corresponds to a depth resolution of about 5 $\mathring{A}$, which is more than one order of magnitude better than conventional RBS using a Si surface barrier detector

Optical and Electrical Effects of p-type μc-SiOx:H in Thin-Film Silicon Solar Cells on Various Front Textures

p-type hydrogenated microcrystalline silicon oxide (µc-Si :H) was developed and implemented as a contact layer in hydrogenated amorphous silicon (a-Si:H) single junction solar cells. Higher transparency, sufficient electrical conductivity, low ohmic contact to sputtered ZnO:Al, and tunable refractive index make p-type µc-Si :H a promising alternative to the commonly used p-type hydrogenated microcrystalline silicon (µc-Si:H) contact layers. In this work, p-type µc-Si :H layers were fabricated with a conductivity of up to 10−2 S/cm and a Raman crystallinity of above 60%. Furthermore, we present p-type µc-Si :H films with a broad range of optical properties (2.1 eV < band gap  eV and 1.6 < refractive index ). These properties can be tuned by adapting deposition parameters, for example, the CO2/SiH4 deposition gas ratio. A conversion efficiency improvement of a-Si:H solar cells is achieved by applying p-type µc-Si :H contact layer compared to the standard p-type µc-Si:H contact layer. As another aspect, the influence of the front side texture on a-Si:H p-i-n solar cells with different p-type contact layers, µc-Si:H and µc-Si :H, is investigated. Furthermore, we discuss the correlation between the decrease of and the cell surface area derived from AFM measurements

Suppression of the increase of high-temperature coercivity in MnBi thin films by Al interlayers

By tailoring the microcrystalline structure of MnBi films, using Al interlayers, a reduction of the high-temperature coercivity by a factor of 3 is achieved. The separation of Bi/Mn bilayers by Al interlayers acts as a diffusion barrier perpendicular to the surface. After annealing, the MnBi layers contain single-domain particles surrounded by an Al matrix exhibiting no significant increase of the coercive field with increasing temperature

Untersuchungen zum Indiumeinbau und zur Relaxation in InGaN‐Schichten für die solareWasserstofferzeugung

Untersuchungen zum Indiumeinbau und zur Relaxation in InGaN-Schichten für die solare Wasserstofferzeugung M. Finken1, B. Holländer2,3, M. Heuken1,4, H. Kalisch1, A. Vescan1 1 RWTH Aachen University, GaN Device Technology, Sommerfeldstrasse 24, 52074 Aachen, Germany 2 Forschungszentrum Jülich GmbH, PGI9-IT, 52425 Jülich, Germany 3 Jülich Aachen Research Alliance, JARA-FIT 4 AIXTRON SE, Kaiserstr. 98, 52134 Herzogenrath, Germany Bei der photoelektrochemischen Synthese von Wasserstoff mit Hilfe von Halbleiterschichten muss ein Optimum für die Bandlücke des verwendeten Materials gefunden werden, das zum einen ein möglichst großes Absorptionsspektrum im sichtbaren Licht besitzt, zum anderen eine ausreichend große Potenzialdifferenz für die Wasserspaltung liefert. Indiumgalliumnitrid ist ein ideales Material für diese Anwendung, da sich die Bandlücke des ternären Halbleiters in Abhängigkeit vom Indiumgehalt zwischen 0,7 eV (InN) und 3,438 eV (GaN) variieren lässt. Aufgrund einer Mischungslücke und des Einflusses von Verspannungen zwischen einer InGaN-Schicht und dem Substrat lassen sich jedoch praktisch nicht beliebig hohe In-Gehalte realisieren. Es wird zunächst der Einfluss der Wachstumstemperatur während der Gasphasenepitaxie auf die Zusammensetzung und die Struktureigenschaften untersucht. Die 100 nm dicken InGaN-Schichten werden mittels Röntgendiffraktometrie und Rutherford-Rückstreu-Spektrometrie untersucht. Dabei zeigt sich, dass der In-Gehalt für niedrigere Temperaturen an der Grenzfläche absättigt. Erst durch das weitere Wachstum und die Relaxation der Schicht kann zur Oberfläche hin mehr Indium eingebaut werden. Dadurch sinkt jedoch die Kristallqualität der wachsenden Schicht. In Zukunft wird untersucht, welchen Einfluss die abnehmende Kristallqualität auf die tatsächliche Effektivität der photoelektrochemischen Erzeugung von Wasserstoff hat. Abbildung 1: Mittels Rutherford-Rückstreu-Spektrometrie bestimmter In-Gehalt an der Oberfläche und an der Grenzfläche zum GaN von 100 nm dicken InGaN Schichten, bezogen auf die Oberflächentemperatur. Zusätzlich 5 µm * 5 µm große AFM Bilder der Oberflächen, jeweils bei 740 °C und 800 °

Wide Gap Microcrystalline Silicon Oxide Emitter for a-SiO x_{x} :H/c-Si Heterojunction Solar Cells

This paper reports on the development of phosphorous doped microcrystalline silicon oxide (µc-SiOx:H) films as an emitter window layer in flat p-type silicon heterojunction (SHJ) solar cells featuring intrinsic a-SiOx:H buffer layers. We investigated the material properties of n-type µc-SiOx:H films grown at various input gas ratios and correlated the results of SHJ solar cells utilizing varying oxygen content and thickness of the emitter layer to the corresponding film properties. A maximum efficiency of 19.0% was achieved. The excellent short circuit current of 35.8 mA/cm2 for flat cells was attributed to the low optical losses in the emitter window

p-Channel Enhancement and Depletion Mode GaN-Based HFETs With Quaternary Backbarriers

Within the last years, III-nitride-based devices have been demonstrated with exceptional performance. There is, however, a severe lack of knowledge when it comes fabrication of p-channel devices. p-Channel heterostructure field-effect transistors (HFETs) could open the way for nitride-based complementary logic. Here, a comprehensive study of enhancement and depletion mode p-channel GaN/AlInGaN HFETs is performed. The influence of a highly p-doped GaN cap layer on device performance is investigated. Gate recessing and changes in composition of the backbarrier are analyzed. ON/OFF ratios of up to 108 and subthreshold swings of about 75 mV/decade are achieved