TY - GEN A1 - Wulf, Ulrich A1 - Richter, Hans T1 - Scale-Invariant Drain Current in Nano-FETs T2 - Journal of Nano Research Y1 - 2010 SN - 1662-5250 VL - 10 SP - 49 EP - 61 ER - TY - GEN A1 - Wulf, Ulrich A1 - Richter, Hans T1 - Scaling in quantum transport in silicon nano-transistors (B4) Y1 - 2010 ER - TY - GEN A1 - Wulf, Ulrich A1 - Krahlisch, Marcus A1 - Richter, Hans T1 - Scaling properties of ballistic nano-transistors T2 - Nanoscale Research Letters Y1 - 2011 SN - 1556-276X VL - 6 IS - 1 ER - TY - GEN A1 - Kouteva-Arguirova, Simona A1 - Orlov, Valeri A1 - Seifert, Winfried A1 - Richter, Hans A1 - Reif, Jürgen T1 - Residual stress distribution and silicon phase transformation induced by Rockwell indentation at different temperatures, studied by means of micro-Raman spectroscopy T2 - Solid State Phenomena Y1 - 2004 SN - 1662-9779 SN - 0377-6883 VL - 95-96 SP - 513 EP - 518 ER - TY - GEN A1 - Orlov, Valeri A1 - Richter, Hans A1 - Fischer, Annette A1 - Reif, Jürgen A1 - Müller, T. A1 - Wahlich, R. T1 - Mechanical Properties of nitrogen-doped CZ silicon crystals T2 - Materials Science in Semiconductor Processing 5 Y1 - 2002 SN - 1369-8001 VL - 5 IS - 4-5 SP - 403 EP - 407 ER - TY - GEN A1 - Wulf, Ulrich A1 - Kucera, Jan A1 - Richter, Hans A1 - Wiatr, Maciej A1 - Höntschel, Jan T1 - Characterization of nanotransistors in a semiempirical model T2 - Thin Solid Films N2 - In a series of recent papers we have established a semiempirical model for quantum transport in a nanotransistor. Here we apply this model to characterize four industrial transistors with gate lengths ranging between 22 nm and 30 nm finding excellent quantitative agreement between theory and experiment. Adjusting our semiempirical model to the experimental output traces, three calibration parameters are found: First, the height of the source–drain barrier, second, the device temperature, and, third, the overlap parameter. The overlap parameter describes the wave function overlap between the source/drain contact and the conduction channel. With the aid of the calibration parameters the considered devices can be classified in three groups: A first group (G1) with good contact-channel coupling and a high saturation current, a second group (G2) with intermediate values and a third group (G3) with poor contact-channel coupling and a small saturation current. We calculate the gate capacitance of the transistors: At threshold voltage a peak of the gate capacitance is observed which is associated with a jump in the overlap parameter. This finding is most pronounced in G1, weaker in G2 and absent in G3. We attribute it to favorable screening conditions in G1 leading to a smooth transition between the contacts and the conduction channel. Our results indicate that this screening effect is favored by an efficient release of the Ohmic heat. KW - Nano-field effect transistor KW - Quantum transport KW - Semiempirical model KW - Quantitative model KW - Compact model KW - Contact-channel coupling KW - Screening properties Y1 - 2016 UR - http://www.sciencedirect.com/science/article/pii/S0040609015009190 U6 - https://doi.org/10.1016/j.tsf.2015.09.041 SN - 0040-6090 VL - 613 SP - 6 EP - 10 ER - TY - GEN A1 - Krahlisch, Marcus A1 - Wulf, Ulrich A1 - Kucera, Jan A1 - Richter, Hans A1 - Höntschel, Jan T1 - Analytical expressions for the drain current of a nanotransistor in the off-state regime T2 - Physica Status Solidi C N2 - Recently, we have suggested a scale-invariant numerical model for a planar nanotransistor based on a Fowler-Nordheim-type of formula. In this this model we introduce a set of approximations to obtain simple analytical expressions for the drain current in the off-state regime. For this purpose the saddle point approximation is applied to the Fowler-Nordheim integral. Furthermore, we are using the WKB-expression for transmission coefficient and a series approximation for Fermi-Dirac integrals by Mc Dougal and Stoner to evaluate the supply function. The resulting analytical formula is in qualitative agreement with the traces of an experimental transistor. It becomes quite simple for small gate voltages, i.e. in the deep off-state regime. Systematic steps to improve our approximations towards a quantitative agreement are discussed. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) Y1 - 2014 UR - http://onlinelibrary.wiley.com/doi/10.1002/pssc.201300122/abstract U6 - https://doi.org/10.1002/pssc.201300122 SN - 1610-1642 VL - 11 IS - 1 SP - 113 EP - 116 ER - TY - CHAP A1 - Richter, Matthias A1 - Lichterman, Michael F. A1 - Hu, Shu A1 - Crumlin, Ethan J. A1 - Axnanda, Stephanus A1 - Favaro, Marco A1 - Drisdell, Walter S. A1 - Hussain, Zahid A1 - Brunschwig, Bruce S. A1 - Liu, Zhi A1 - Lewis, Nathan S. A1 - Lewerenz, Hans-Joachim T1 - Experimental Approach for Determining Semiconductor/liquid Junction Energetics by Operando Ambient Pressure X-ray Photoelectron Spectroscopy T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft N2 - The performance of a photoelectrochemical solar cell depends strongly on the electrochemical nature of the semiconductor/electrolyte junction [1]. Operando Ambient Pressure X-ray photoelectron spectroscopy investigation of semiconductor/liquid junctions provides quantitative understanding of the energy bands in these photoelectrochemical solar cells [2, 3, 4]. We demonstrate how OAP-XPS may be used to determine these relationships for semiconductor/liquid systems. The data can be analyzed to determine the energy relationship between the electronic energy bands in the semiconductor electrode and the redox levels in the solution. The major conditions for semiconductor-electrolyte contacts including accumulation, depletion, and Fermi-level pinning are observed, and the so-called flat-band energy can be determined. [1] Science 344 (2014) 1005; [2] Sci Rep 5 (2015) 9788; [3] Ener Sci 8 (2015) 2409; [4] J Electrochem Soc 162 (2016) H1 KW - in operando KW - ambient pressure spectroscopy KW - water splitting Y1 - 2016 UR - http://www.dpg-verhandlungen.de/year/2016/conference/regensburg/part/o/session/72/contribution/10?lang=en SP - S. 409 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Lichterman, Michael F. A1 - Richter, Matthias A1 - Hu, Shu A1 - Crumlin, Ethan J. A1 - Axnanda, Stephanus A1 - Favaro, Marco A1 - Drisdell, Walter S. A1 - Hussain, Zahid A1 - Brunschwig, Bruce S. A1 - Liu, Zhi A1 - Lewis, Nathan S. A1 - Lewerenz, Hans-Joachim T1 - Probing the TiO2/Liquid Interface of a Photoelectrochemical Cell by X-Ray Photoelectron Spectroscopy T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft N2 - Amorphous TiO2 coatings can stabilize semiconductor photoanodes such as Si, GaAs, and GaP that are otherwise unstable in aqueous media [1]. Using tender X-rays with their substantially increased inelastic mean free scattering length of photoelectrons and using the classical three-electrode potentiostatic arrangement allows one to follow of the influence of the applied potentials on the semiconductor electrode energetics such as band bending and band edge shifts directly [2, 3]. The observed shifts in binding energy with respect to the applied potential have directly revealed rectifying junction behavior on semiconducting samples. Accumulation, depletion and Fermi level pinning were observed. Additionally, the non-linear response of the core level binding energies to changes in the applied electrode potential has revealed the influence of defect-derived electronic states on the Galvani potential across the complete cell. [1] Science 344 (2014) 1005; [2] Sci Rep 5 (2015) 9788; [3] Ener & Env Sci 8 (2015) 2409 KW - X-Ray photoelectron spectroscopy KW - phototanodes KW - TiO2 passivation KW - water splitting Y1 - 2016 UR - http://www.dpg-verhandlungen.de/year/2016/conference/regensburg/part/o/session/82/contribution/1?lang=en SP - S. 414 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Richter, Matthias A1 - Lichterman, Michael F. A1 - Hu, Shu A1 - Crumlin, Ethan J. A1 - Axnanda, Stephanus A1 - Favaro, Marco A1 - Drisdell, Walter S. A1 - Hussain, Zahid A1 - Brunschwig, Bruce S. A1 - Liu, Zhi A1 - Lewis, Nathan S. A1 - Lewerenz, Hans-Joachim T1 - An Electrochemical, resonant Photoemission and Ambient Pressure-X-ray Photoelectron Spectroscopic Investigation of Si/TiO2/Ni/Electrolyte Interfaces T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft N2 - Photoelectrochemical cells based on semiconductor-liquid interfaces provide a method of converting solar energy to electricity or fuels. Recently, we have demonstrated operational systems that involved stabilized semiconductor-liquid junctions [1]. The electrical and spectroscopic properties of the TiO2/Ni protection layer system have been investigated in contact with electrolyte solutions [2, 3, 4]. From the response of the photoelectron binding energies to variations in applied potential the energetics of the solid/electrolyte interface are elucidated. The degree of conductivity depended on the chemical state of the Ni on the TiO2 surface. The combinations of these techniques provide a powerful tool for the investigation of hybrid electrode/solution contacts. [1] Science 344 (2014) 1005; [2] Sci Rep 5 (2015) 9788; [3] Ener & Env Sci 8 (2015) 2409; [4] J Electrochem Soc 162 (2016) H1 KW - resonant photoelectron spectroscopy KW - ambient pressure spectroscopy KW - water splitting Y1 - 2016 UR - http://www.dpg-verhandlungen.de/year/2016/conference/regensburg/part/o/session/82/contribution/2?lang=en SP - S. 414 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - GEN A1 - Käso, Mathias A1 - Wulf, Ulrich A1 - Kucera, Jan A1 - Richter, Hans A1 - Höntschel, Jan T1 - Thermal properties of quantum devices in integrated circuits embedded in a chip environment T2 - Physica Status Solidi C N2 - We consider a thermal model for an integrated circuit including its chip environment. As the simplest choice, the active device layer (integrated circuit) consists of an array of replicas of the same quantum device with the same time depended average temperature. Modeling the chip environment we assume this active layer is sandwiched between two coplanar heat reservoirs. The top heat reservoir represents the wiring layer of the chip (‘back-end of line’). Its temperature is predominantly determined by the dissipated Joule heat in the wiring, typically in the order of one hundred degrees of Celsius. The bottom reservoir represents the cooling unit at about room-temperature. We solve the coupled equations describing thermal transport between the active layer and surrounding heat reservoirs and electrical transport in the quantum devices. The stationary working temperatures of the considered quantum devices can be found from a fix-point problem. A proper linearization of the complete time-depended problem yields the stability of these fixpoints. Numerical solutions for a device layer consisting of identical nano-transistors are given for selected parameters. KW - Thermal properties of quantum devices KW - Transport KW - Chip Y1 - 2014 U6 - https://doi.org/10.1002/pssc.201300203 SN - 1610-1642 N1 - E-MRS 2013 Spring Meeting Symposium VL - 11 IS - 1 SP - 105 EP - 108 ER - TY - GEN A1 - Wulf, Ulrich A1 - Kučera, Jan A1 - Richter, Hans A1 - Horstmann, Manfred A1 - Wiatr, Maciej A1 - Höntschel, Jan T1 - Channel Engineering for Nanotransistors in a Semiempirical Quantum Transport Model T2 - Mathematics N2 - One major concern of channel engineering in nanotransistors is the coupling of the conduction channel to the source/drain contacts. In a number of previous publications, we have developed a semiempirical quantum model in quantitative agreement with three series of experimental transistors. On the basis of this model, an overlap parameter 0≤C≤1 can be defined as a criterion for the quality of the contact-to-channel coupling: A high level of C means good matching between the wave functions in the source/drain and in the conduction channel associated with a low contact-to-channel reflection. We show that a high level of C leads to a high saturation current in the ON-state and a large slope of the transfer characteristic in the OFF-state. Furthermore, relevant for future device miniaturization, we analyze the contribution of the tunneling current to the total drain current. It is seen for a device with a gate length of 26 nm that for all gate voltages, the share of the tunneling current becomes small for small drain voltages. With increasing drain voltage, the contribution of the tunneling current grows considerably showing Fowler–Nordheim oscillations. In the ON-state, the classically allowed current remains dominant for large drain voltages. In the OFF-state, the tunneling current becomes dominant. KW - nanotransistor KW - channel engineering KW - quantum transport KW - contact-to-channel coupling KW - wave function overlap KW - tunneling current Y1 - 2017 UR - http://www.mdpi.com/2227-7390/5/4/68 U6 - https://doi.org/10.3390/math5040068 SN - 2227-7390 VL - 5 IS - 4 ER - TY - GEN A1 - Brinkert, Katharina A1 - Richter, Matthias A1 - Akay, Ömer A1 - Liedtke, Janine A1 - Giersig, Michael A1 - Fountaine, Katherine T. A1 - Lewerenz, Hans-Joachim T1 - Efficient Solar Hydrogen Generation in Microgravity Environment T2 - Nature Communications N2 - Long-term space missions require extra-terrestrial production of storable, renewable energy. Hydrogen is ascribed a crucial role for transportation, electrical power and oxygen generation. We demonstrate in a series of drop tower experiments that efficient direct hydrogen production can be realized photoelectrochemically in microgravity environment, providing an alternative route to existing life support technologies for space travel. The photoelectrochemical cell consists of an integrated catalyst-functionalized semiconductor system that generates hydrogen with current densities >15 mA/cm2 in the absence of buoyancy. Conditions are described adverting the resulting formation of ion transport blocking froth layers on the photoelectrodes. The current limiting factors were overcome by controlling the micro- and nanotopography of the Rh electrocatalyst using shadow nanosphere lithography. The behaviour of the applied system in terrestrial and microgravity environment is simulated using a kinetic transport model. Differences observed for varied catalyst topography are elucidated, enabling future photoelectrode designs for use in reduced gravity environments. Y1 - 2018 U6 - https://doi.org/10.1038/s41467-018-04844-y SN - 2041-1723 IS - 9 ER - TY - GEN A1 - Brinkert, Katharina A1 - Richter, Matthias A1 - Akay, Ömer A1 - Giersig, Michael A1 - Fountaine, Katherine T. A1 - Lewerenz, Hans-Joachim T1 - Advancing semiconductor-electrocatalyst systems: application of surface transformation films and nanosphere lithography T2 - Faraday Discussions N2 - Photoelectrochemical (PEC) cells offer the possibility of carbon-neutral solar fuel production through artificial photosynthesis. The pursued design involves technologically advanced III–V semiconductor absorbers coupled via an interfacial film to an electrocatalyst layer. These systems have been prepared by in situ surface transformations in electrochemical environments. High activity nanostructured electrocatalysts are required for an efficiently operating cell, optimized in their optical and electrical properties. We demonstrate that shadow nanosphere lithography (SNL) is an auspicious tool to systematically create three-dimensional electrocatalyst nanostructures on the semiconductor photoelectrode through controlling their morphology and optical properties. First results are demonstrated by means of the photoelectrochemical production of hydrogen on p-type InP photocathodes where hitherto applied photoelectrodeposition and SNL-deposited Rh electrocatalysts are compared based on their J–V and spectroscopic behavior. We show that smaller polystyrene particle masks achieve higher defect nanostructures of rhodium on the photoelectrode which leads to a higher catalytic activity and larger short circuit currents. Structural analyses including HRSEM and the analysis of the photoelectrode surface composition by using photoelectron spectroscopy support and complement the photoelectrochemical observations. The optical performance is further compared to theoretical models of the nanostructured photoelectrodes on light scattering and propagation. KW - shadow nanosphere lithography (SNL) KW - electrocatalyst nanostructures KW - Rh electrocatalysts KW - InP photocathodes Y1 - 2018 U6 - https://doi.org/10.1039/C8FD00003D SN - 1359-6640 SN - 1364-5498 VL - 208 SP - 523 EP - 535 ER -