Lecture

Transport & Recombination

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In course

MICRO-566: Large-area electronics: devices and materials

Introduction to the physical concepts involved in the description of optical and electronic transport properties of thin-film semiconductor materials found in many large-area applications (solar cells, displays, imagers, etc) and introduction to the physic ...

Description

This lecture covers the transport and recombination processes in large area electronic materials, focusing on topics such as recombination in dangling bonds, charge state representation, recombination in doped and undoped a-Si:H, total recombination, dark conductivity, primary and secondary photoconductivity, defect density, trapping conduction, and transient photoconductivity. The instructor discusses various characterization techniques, including steady-state photoconductivity, constant photocurrent measurement, and transient photocurrent spectroscopy, highlighting the importance of understanding recombination mechanisms in different semiconductor materials.

Instructors (2)

Christophe Ballif

Christophe Ballif is director of the Phototovoltaics and Thin Film Electronics Laboratoryb) (PV-Lab at the institute of microengineering (IMT) in Neuchâtel (part of the EPFL since 2009). The lab focus is on the science and technology of high efficiency heterojunction crystalline cells,so-called passivating contacts for solar cells, multi-junction solar cells include novel generation Perovskite on innovative optical high speed detector and on various macroelectronics application. It also deals with energy management with a focus on integration of solar electricity into the energy system. The PV-Lab has strongly contributed to technology transfer and industrialization of novel devices and full technology with numerous companies. Christophe Ballif graduated as a physicist from the EPFL in 1994, where he also obtained in 1998 his Phd degree working on novel PV materials. He accomplished his postdoctoral research at NREL (Golden, US) on compound semiconductor solar cells (CIGS and CdTe). He worked then at the Fraunhofer ISE (Ge) on crystalline silicon photovoltaics (monocrystalline and multi-crystalline) until 2003 and then at the EMPA in Thun (CH) before becoming full professor at the University of Neuchâtel IMT in 2004, taking over the chair of Prof. A. Shah. Since 2013, C.Ballif is also the director of the new CSEM PV-Center, also located in Neuchâtel. The CSEM PV-Center is focussing more on industrialisation and technology transfer in the field of solar energy, including solar electricity management and storage. At the core of the CSEM PV-center activities lies several "pilot lines" for various kinds of solar cells manufacturing, with a focus coating technologies, wet chemistry processes for crystalline silicon, metalisation techniques for solar cells, and a platform for developing "ideal packaging solutions and polymers" for PV modules. In addition, joined facitilites between CSEM and EPFL of over 800 m2 are available for modules manufacturing, measuring and accelerated aging. CSEM PV-center has also full team dedicated to storage and energy systems and operates a joined center with BFH in Biel for research on electrochemical storage. He (co-) authored over 500 journal and technical papers, as well as several patents. He is an elected member of the SATW, member of the scientific council of the Swiss AEE, and member of the board of the EPFL Energy center. In 2016, he recieved the Becquerel prize for his contributions to the field of high efficiency photovoltaics.

Franz-Josef Haug

I studied Physics between 1990 and 1996 at the Universities of Ulm (Germany) and Waikato (New Zealand). While specializing mostly on Theoretical Physics and Quantum Theory during my studies, I turned towards Experimental Physics for a graduate work on gas-phase epitaxy of silicon. After that, I pursued a PhD program at ETH Zürich (Switzerland), studying Cu(In,Ga)Se2 solar cells. As PostDoc, I went to EMPA (Switzerland) to work on plasma processes for hard coatings of TiN and to the Jülich Research Centre in Germany to study light scattering ZnO front contacts for solar cells. In 2005 I joined the Institute of Microengineering (IMT) at the University of Neuchatel to lead a research group on thin film silicon solar cells within the PV-Lab. In 2009 the IMT was integrated into EPFL. My main research interests are optics, charge transport in semiconductors and renewable energy in general. My current work is devoted to passivating contacts for crystalline silicon solar cells, using thin silicon films as contact layers. In 2015 I was appointed Maitre d'Enseignement et Recherche (Senior Lecturer and Scientist) and member of the Faculty of STI. From 2013 to 2015 I was member of the EFPL Teachers Council (CCE) and from 2016 and 2018 I was elected into the Council of the Engineering School (CF-STI). In 2020 I was elected to become a member of CF-STI. My main objective for the legislature is to represent the role of EPFL's intermediate staff and to raise the awareness for concerns of the satellite campuses.

Official source

Ontological neighbourhood

Physics

Condensed matter physics: Solid-state physics

Related concepts (32)

Semiconductor

A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way. Its conducting properties may be altered in useful ways by introducing impurities ("doping") into the crystal structure. When two differently doped regions exist in the same crystal, a semiconductor junction is created.

Schottky defect

A Schottky defect is an excitation of the site occupations in a crystal lattice leading to point defects named after Walter H. Schottky. In ionic crystals, this defect forms when oppositely charged ions leave their lattice sites and become incorporated for instance at the surface, creating oppositely charged vacancies. These vacancies are formed in stoichiometric units, to maintain an overall neutral charge in the ionic solid. Schottky defects consist of unoccupied anion and cation sites in a stoichiometric ratio.

Crystallographic defect

A crystallographic defect is an interruption of the regular patterns of arrangement of atoms or molecules in crystalline solids. The positions and orientations of particles, which are repeating at fixed distances determined by the unit cell parameters in crystals, exhibit a periodic crystal structure, but this is usually imperfect. Several types of defects are often characterized: point defects, line defects, planar defects, bulk defects. Topological homotopy establishes a mathematical method of characterization.

Frenkel defect

In crystallography, a Frenkel defect is a type of point defect in crystalline solids, named after its discoverer Yakov Frenkel. The defect forms when an atom or smaller ion (usually cation) leaves its place in the lattice, creating a vacancy and becomes an interstitial by lodging in a nearby location. In elemental systems, they are primarily generated during particle irradiation, as their formation enthalpy is typically much higher than for other point defects, such as vacancies, and thus their equilibrium concentration according to the Boltzmann distribution is below the detection limit.

Semiconductor device

A semiconductor device is an electronic component that relies on the electronic properties of a semiconductor material (primarily silicon, germanium, and gallium arsenide, as well as organic semiconductors) for its function. Its conductivity lies between conductors and insulators. Semiconductor devices have replaced vacuum tubes in most applications. They conduct electric current in the solid state, rather than as free electrons across a vacuum (typically liberated by thermionic emission) or as free electrons and ions through an ionized gas.

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