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Recently, chalcogenide glass based phase change materials (PCMs) have shown utility as a tuning material for a range of nanophotonic devices. Owing to their low loss, ultrafast switching speeds and wide waveband operation, PCMs are integrated in an increasing number of next generation tunable components, including integrated photonic switches, metasurface optics and tunable spectral filters. Nonetheless, modelling of PCM-based devices is challenging, both in terms of accurate representation of experimentally-derived material properties in different phase states, and standardization of results across the research community. In this work, we introduce PCMnet, an online database of the complex refractive indices of a variety of chalcogenide glass PCMs (such as GeSbTe), as an accessible and indexed repository for data sharing across the PCM community. Refractive indices (n) and extinction coefficients (k) between amorphous and crystalline states are directly extracted from experimentally-derived data in numerous academic research articles, and collated into the material resource database. Due to the inaccuracies associated with our data collection methods, this data is supplemented with additional computationally-generated data, obtained through WVASE, a commercial ellipsometry analysis software package. To demonstrate the utility of PCMnet, we provide a NASA application-driven device optimization example using the optical properties of PCMs collected with our database. We anticipate the database providing great use to the PCM community and coordinated research efforts enabled by PCMnet will promote the shared repository for the selection of appropriate PCMs for tunable nanophotonic device design for a range of applications., Comment: 19 pages, 8 figures, 1 table

© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This paper begins with a comprehensive review into the existing GaN device models. Secondly, it identifies the need for a more accurate GaN switching model. A simple practical process based on radio frequency techniques using vector network analyser is introduced in this paper as an original contribution. It was applied to extract the impedances of the GaN device to develop an efficient behavioural model. The switching behaviour of the model was validated using both simulation and real time double pulse test experiments at 500 V, 15 A conditions. The proposed model is much easier for power designers to handle, without the need for knowledge about the physics or geometry of the device. The proposed model for Transphorm GaN HEMT was found to be 95.2% more accurate when compared to the existing LT-spice manufacturer model. This work additionally highlights the need to adopt established RF techniques into power electronics to reduce the learning curve while dealing with these novel high-speed switching devices.

International audience; Energy storage systems are key elements for enabling the design of MicroGrids in buildings, specially to deal with stochastic renewable energy resources and to promote peak shifting. However, inaccuracies in the batteries' mathematical models due to temperature and ageing effects can reduce the performance of a MicroGrid system. To tackle these uncertainties, this article presents a two-level hierarchical model predictive controller empowered with a data-driven algorithm for real-time model identification of Lithium-ion batteries. The objective is to enhance their state of charge estimation and to make their maximum use without damaging them. The results demonstrate that it improves up to three times the accuracy of state-of-charge estimation and increases about 3% the annual building MicroGrid selfconsumption rate. Furthermore, the division of the building MicroGrid energy management system into two hierarchical levels soften the drawbacks arise from the inaccuracies of day-ahead data prediction while reducing the computational cost. The proposed architecture guarantees higher energetic autonomy indexes than a conventional rule-based controller in all scenarios under study.

The authors thank the SUMIDA Components & Modules GmbH in Obernzell, Germany, for manufacturing or machining most of the ferrite cores which were used to generate the presented measurement results. Proceedings of the 22nd European Conference on Power Electronics and Applications (EPE'20 ECCE Europe), held 7-11 September 2020 in Lyon, France., Parts of the work presented in this paper have been supported by the German Federal Ministry of Education and Research (BMBF). Project funding reference number: 16EMO0234.

This paper presents an innovative and automated measurement setup for the characterization of variability effects in CMOS transistors using array-based integrated circuits, through which a better understanding of CMOS reliability could be attained. This setup addresses the issues that come with the need for a trustworthy statistical characterization of these effects: testing a very large number of devices accurately but, also, in a timely manner. The setup consists of software and hardware components that provide a user-friendly interface to perform the statistical characterization of CMOS transistors. Five different electrical tests, comprehending time-zero and time-dependent variability effects, can be carried out. Test preparation is, with the described setup, reduced to a few seconds. Moreover, smart parallelization techniques allow reducing the typically timeconsuming aging characterization from months to days or even hours. The scope of this paper thus encompasses the methodology and practice of measurement of CMOS time-dependent variability, as well as the development of appropriate measurement systems and components used in efficiently generating and acquiring the necessary electrical signals

Birefringence and optical losses in the optical sensor head of a Faraday effect based, high accuracy and high bandwidth current measurement system lead to changes of the polarisation state and orientation. These changes, if not properly determined and calibrated, lead to systematic measurement errors. Therefore, a calibration method for the optical current measurement system focusing on pulse current applications is proposed. The procedure is based on a zero-current measurement and a full (Stokes) polarimeter. It determines the full polarisation state and orientation of a beam propagating through the optical system. The calibration method then allows to determine the parasitic linear birefringence caused by any subsequent optical element in the system. Eventually, an error analysis characterising the potential error reduction by the proposed calibration method is conducted. Further, the additionally introduced error sources caused by the full polarimeter approach are characterised., 2020 22nd European Conference on Power Electronics and Applications (EPE'20 ECCE Europe), ISBN:978-9-0758-1536-8, ISBN:978-1-7281-9807-1

In this paper a method is presented to accurately and quickly interpolate a dataset of the complex refractive index of arbitrary compound semiconductors. The method is based on a parameter morphing algorithm which maps critical points of two endpoint materials with known optical parameter sets onto each other. Every desired intermediate material composition can be interpolated if the composition dependence of the band gap is known for the given material system. The accuracy and stability of the proposed procedure is validated experimentally using spectral ellipsometry and reflection measurements. Test samples of two III–V semiconductor material systems, AlGaAs and GaInAsP, with various compositions were grown using metalorganic vapour phase epitaxy and the morphed parameter sets are compared to corresponding measurement results. Modelling the absorption of a solar cell device and comparing it to the external quantum efficiency is presented as an application example of this method. The interpolation method is demonstrated to be a powerful tool for optical and electro-optical modelling of semiconductor structures if parameters of the complex refractive index are not available for the exact material composition.

Kesterite semiconductors, derived from the mineral Cu2(Zn,Fe)SnS4, adopt superstructures of the zincblende archetype. This family of semiconductors is chemically flexible with the possibility to tune the physical properties over a large range by modifying the chemical composition, while preserving the same structural backbone. In the simplest case, three metals (e.g. Cu, Zn and Sn) occupy the cation sublattice, which gives rise to a range of competing orderings (polymorphs) and the possibility for order–disorder transitions. The rich physics of the sulphide, selenide, and mixed-anion materials make them attractive for computer simulations in order to provide deeper insights and to direct experiments to the most promising material combinations and processing regimes. This topical review assesses the status of first-principles electronic structure calculations, optical modelling, and photovoltaic device simulations of kesterite semiconductors. Recent progress is discussed, and immediate challenges are outlined, in particular towards overcoming the voltage deficit in Cu2ZnSnS4 and Cu2ZnSnSe4 solar cells.

Proceedings der Konferenz 19th European Conference on Power Electronics and Applications (EPE'17 ECCE Europe) vom 11-14 Sept. 2017 in Warschau, Polen., Parts of the work presented in this paper have been supported by the German Federal Ministry for Economic Affairs and Energy (BMWi). Project funding reference number: 0324106A.

This paper investigates process-induced variations of the open-circuit voltage (Voc) using voltage-dependent quantum efficiency measurements. By means of device modelling we show that this method is able to explain the Voc difference of two solar cells, even if they show identical electrical behaviour under short-circuit condition. This paper furthermore explains how the origin of Voc variations can be classified into emitter, base and rear of the solar cell. The simulation results have been experimentally verified with industrial-type passivated emitter and rear cells (PERC) cells made from p-type Czochralski wafers. The proposed analysis method is an attractive way for monitoring Voc variations of solar cells in industrial mass production since there is no need for specially prepared test structures. © 2017 The Authors. Published by Elsevier Ltd.

The nano-contact spin torque oscillator (NC-STO) is an emerging device for highly tunable microwave frequency generation in the range from 0.1 GHz to above 65 GHz with an on-chip footprint on the scale of a few μm. The frequency is inherent to the magnetic material of the NC-STO and is excited by an electrical DC current by means of the spin torque transfer effect. Although the general operation is well understood, more detailed aspects such as a generally nonlinear frequency versus current relationship, mode-jumping and high device-to-device variability represent open questions. Further application-oriented questions are related to increasing the electrical output power through synchronization of multiple NC-STOs and integration with CMOS integrated circuits. This thesis consists of an experimental part and a simulation part. Experimentally, for the frequency stability it is found that the slow but strong 1/f-type frequency fluctuations are related to the degree of nonlinearity and the presence of perturbing, unexcited modes. It is also found that the NC-STO can exhibit up to three propagating spin wave oscillation modes with different frequencies and can randomly jump between them. These findings were made possible through the development of a specialized microwave time-domain measurement circuit. Another instrumental achievement was made with synchrotron X-rays, where we image dynamically the magnetic internals of an operating NC-STO device and reveal a spin wave mode structure with a complexity significantly higher than the one predicted by the present theory. In the simulations, we are able to reproduce the nonlinear current dependence by including spin wave-reflecting barriers in the nm-thick metallic, magnetic free layer. A physical model for the barriers is introduced in the form of metal grain boundaries with reduced magnetic exchange coupling. Using the experimentally measured average grain size of 30 nm, the spin wave mode structure resulting from the grain model is able to reproduce the experimentally found device nonlinearity and high device-to-device variability. In conclusion, the results point out microscopic material grains in the metallic free layer as the reason behind the nonlinear frequency versus current behavior and multiple propagating spin wave modes and thereby as a source of device-to-device variability and frequency instability. Dagens snabba utveckling inom informationsteknik drivs på av ständigt växande informationsmängder och deras samhällsanvändning inom allt från resursoptimering till underhållning. Utvecklingen möjliggörs till stor del hårdvarumässigt av miniatyrisering och integrering av elektroniska komponenter samt trådlös kommunikation med allt större bandbredd och högre överföringshastighet. Det senare uppnås främst genom utnyttjande av högre radiofrekvenser i teknologiskt tidigare oåtkomliga delar av spektrumet. Frekvensutnyttjandet har det senaste årtiondet ökat markant i mikrovågsområdet med typiska frekvenser runt 2.4 GHz och 5.2-5.8 GHz. I den spinntroniska oscillatorn (STO:n) möjliggörs frekvensgenerering i det breda området från 0.1 GHz upp till över 65 GHz av en komponent med mikrometerstorlek som kan integreras direkt i CMOS-mikrochip. Till skillnad från i konventionella radiokretsar med oscillatorer konstruerade av integrerade transistorer och spolar, genereras mikrovågsfrekvensen direkt i STO:ns magnetiska material och omvandlas därefter till en elektrisk signal genom komponentens magnetoresistans. Dessa materialegenskaper möjliggör ett tillgängligt frekvensband med extrem bredd i en och samma STO, som därtill kan frekvensmoduleras direkt genom sin styrström och på så sätt förenklar konstruktionen av sändarsystem. STO:ns icke-linjära egenskaper kan potentiellt också användas för att i en och samma komponent blanda ned mottagna mikrovågssignaler och på så sätt förenkla konstruktionen även av mikrovågsmottagare. STO:ns signalegenskaper bestäms av det magnetiska materialets fysik i form av magnetiseringsdynamik driven av elektriskt genererade spinnströmmar. I denna avhandling studeras denna dynamik experimentellt med särskilt fokus på frekvensstabiliteten i den hittills mest stabila STO-typen; nanokontakts-STO:n. Genom mätningar i tidsdomän av STO:ns elektriska signaler runt 25 GHz har frekvensstabiliteten funnits hänga samman med den typ av icke-linjärt beteende som också funnits vara utmärkande för tillverkningsvariationen i komponenterna. Mikroskopiska undersökningar av materialet visar att en trolig källa till denna variation är den magnetiska metallens uppbyggnad i form av korn i storleksordningen 30 nm, och datorsimuleringar av en sådan materialstruktur har visats kunna reproducera de experimentella resultaten. Därtill har en metod utvecklats för att med röntgenstrålning direkt mäta de små, magnetiska mikrovågsrörelserna i materialet. Denna röntgenteknik möjliggör detaljerade experimentella studier av magnetiseringsdynamiken och kan användas för att verifiera och vidareutveckla den existerande teorin för mikrovågsspinntronik. Sammantaget förs STO-teknologin genom denna studie ett steg närmare sina tänkbara samhällsbreda tillämpningar inom snabb, trådlös kommunikation för massproducerade produkter med integrerad sensor- och datorfunktionalitet. QC 20160620

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Doutoramento em Engenharia Electrotécnica Nowadays, wireless communications systems demand for greater mobility and higher data rates. Moreover, the need for spectral efficiency requires the use of non-constant envelope modulation schemes. Hence, power amplifier designers have to build highly efficient, broadband and linear amplifiers. In order to fulfil these strict requirements, the practical Doherty amplifier seems to be the most promising technique. However, due to its complex operation, its nonlinear distortion generation mechanisms are not yet fully understood. Currently, only heuristic interpretations are being used to justify the observed phenomena. Therefore, the main objective of this work is to provide a model capable of describing the Doherty power amplifier nonlinear distortion generation mechanisms, allowing the optimization of its design according to linearity and efficiency criteria. Besides that, this approach will allow a bridge between two different worlds: power amplifier design and digital pre-distortion since the knowledge gathered from the Doherty operation will serve to select the most suitable pre-distortion models. Presentemente, os sistemas de comunicações sem fios exigem uma maior mobilidade e elevadas taxas de transferência. Para além disso, a necessidade de eficiência espectral obriga ao uso de esquemas de modulação de envolvente variável. Consequentemente, o desenvolvimento de amplificadores de elevada eficiência, com uma elevada largura de banda e, ao mesmo tempo, lineares, tornou-se num dos maiores desafios para os engenheiros de projeto de amplificadores de potência. Por forma a cumprir estes requisitos muito rigorosos, o amplificador em configuração Doherty parece ser a técnica mais promissora. Contudo, devido à sua complexa operação, os seus mecanismos de geração de distorção não linear não são ainda completamente conhecidos. Atualmente, apenas interpretações heurísticas estão a ser usadas para justificar os fenómenos observados. Nesse sentido, o principal objetivo deste trabalho é desenvolver um modelo capaz de descrever os mecanismos de geração da distorção não linear em amplificadores Doherty, permitindo assim, a optimização do seu projeto, tendo em conta as especificações de linearidade e eficiência. Para além disso, esta abordagem permitirá uma ponte entre dois mundos diferentes: projecto de amplificadores de potência e pré-distorção digital, uma vez que o conhecimento recolhido da operação do Doherty ajudará na escolha de modelos de pré-distorção mais adequados.

International audience; This paper discusses a design methodology for power electronic converters according to the Global Energy Requirement (GER) criterion, i.e. the primary energy consumption over their entire life cycle. For given specifications of the converter, each power component of a self-oscillating flyback converter and the main control parameters are optimized using scaling laws for given technologies. Models linking sizes of components, loss parameters and embodied energy parameters are presented. Finally a comparison is realized between a GER-designed converters and a classical one (designed from thermal criteria) which concludes to an improvement of efficiency for a given consumption profile.

Semiconductor quantum dot laser is a recent class of laser sources which is an alternative to the conventional bulk and quantum well lasers. In the development of laser sources an important step concerns the modeling of the devices to be realized, and this requires the use of good methods able to incorporate various physical phenomena present in real devices. In this paper we show in details the implementation of a quantum dot laser simulator and apply it to simulate the switching-on behavior and other characteristics of a real quantum dot laser source. The description here presented intends to be a help for teaching or even basic-research in that particular field of optoelectronics. Laser de pontos quânticos semicondutores é uma recente classe de fontes laser que se apresenta como alternativa aos lasers de poços quânticos. Durante o desenvolvimento de fontes laser um passo importante consiste na modelagem dos dispositivos a serem realizados, e isto requer o uso de bons métodos, capazes de incorporar vários fenômenos físicos presentes em dispositivos reais. Neste artigo mostramos em detalhes a implementação de um simulador de laser de pontos quânticos e o aplicamos na simulação do comportamento de switching-on e outras características de uma fonte laser de pontos quânticos real. A descrição aqui apresentada pretende auxiliar o ensino ou mesmo a pesquisa básica nessa sub-área da optoeletrônica.

International audience; This paper addresses the behavior of low voltage MOSFETs under breakdown avalanche operation. The phenomena leading to avalanche operation of the MOSFET transistors in automotive applications are first presented. Then, after a brief description of the model and of the experimental identification of its parameters, electrothermal simulations are performed. A special focus is given to the current balance between paralleled MOSFETs, because in this case breakdown voltage mismatches are a well-known reliability issue. These simulations demonstrate the influence of the specific avalanche path resistance on current sharing. Calculations performed using the proposed model give results far less pessimistic (lower temperature rise on the most stressed transistor) than classical temperature-dependant-only avalanche models. This avoids expensive specifications narrowing when designing for mass-market applications (where wide manufacturing dispersions occur).

The solar cell technology based on Cu(In,Ga)Se2 (CIGS) thin-films provides a promising route to cost competitive solar electricity. The standard device structure is ZnO:Al/ZnO/CdS/CIGS/Mo films on a glass substrate, where the first three layers are n-type semiconductors with wide bandgaps, forming a pn-junction with the p-type CIGS absorber layer; the Mo layer serves as a back contact. This thesis deals with analysis of the generation and recombination of electron-hole pairs throughout the device. These processes determine the maximum output power: generation limits the current; recombination limits the voltage. The generation is calculated with an optical model based on complex refractive indices determined for the individual layers. The main features of the optical response of the solar cell can be reproduced with a specular model neglecting scattering. A model including ideally Lambertian scattering at the front and back surface of the CIGS absorber layer is introduced to investigate the possibility to maintain a high current generation with thin absorber layers. The result highlights the relatively poor optical performance of the Mo back contact. TiN and ZrN are explored as alternatives, and improved optical performance is experimentally demonstrated for both materials. The recombination analysis emphasizes that, in general, more than one recombination path of comparable magnitude are operative in parallel. For cells with absorber bandgap increasing from 1.0 eV (CuInSe2) to 1.7 eV (CuGaSe2), a relative increase of interface recombination is found. When these cells are subject to accelerated ageing, degradation is smallest for intermediate bandgaps; an explanation involving different sensitivity to decreased absorber band bending and activation of grain boundaries is suggested. The optical gain with ZrN back contacts is counteracted by increased back contact recombination and contact resistance, but an intermediate layer of MoSe2 is shown to alleviate these problems, allowing for an overall improved efficiency.