Tutorials

A series of tutorials are planned for Sunday, August 18 suitable for students and researchers interested in learning more about amorphous and nanocrystalline semiconductors. There will be two plenary sessions in the morning on charge transport in disordered materials and photovoltaics, and three parallel sessions in the afternoon specializing in thin film silicon and oxides, chalcogenides, and organic semiconductors. Fees for the tutorials are listed on the registration page.

A booklet of the tutorials can be downloaded here. --> Tutorials

  Tutorial Program
8:30–10:00 Generation, Transport, and Recombination of Charge Carriers in Amorphous Semiconductors
Sergei Baranovski, Philipps Universität Marburg, Germany
10:00–10:15 coffee break
10:15–11:45 Thin-film Photovoltaics
Sigurd Wagner, Princeton University, USA

Slides
noon–1:00 lunch (provided)
 

Session A
Chalcogenides

Session B
Thin Film Silicon and TCO
Session C
Organic Electronics
1:00–2:30 Chalcogenide Semiconductors: Fundamental Physics
Koichi Shimakawa
Gifu University, Japan
Amorphous Oxide Semiconductor TFTs and Applications
Arokia Nathan
University of Cambridge, UK
Optical and Electronic Properties of Organic Semiconductors
Robert A. Street
Palo Alto Research Center, USA
2:30–2:45 coffee break
2:45–4:15 Phase Change Memory Materials
John Robertson
University of Cambridge, UK
Thin Film Silicon Electronic Devices
Jin Jang
Kyung Hee University
Republic of Korea
Organic Optoelectronic Devices
Hany Aziz
University of Waterloo, Canada

Generation, Transport, and Recombination of Charge Carriers in Amorphous Semiconductors
Sergei Baranovski, Philipps Universität Marburg, Germany

Interest in the optoelectronic properties of amorphous organic and inorganic semiconductors has been steeply growing in the last decades. This is caused by successful current applications of such materials in various devices and by their promise for future applications, particularly for large-area devices. Amorphous semiconductors dominate already the electrophotographic image recording on the industrial scale and they are becoming more and more important for applications in light-emitting diodes, in field-effect transistors, and in solar cells. The processes of charge carrier generation and recombination play the decisive role for device applications of amorphous materials. The current state of research related to these processes will be reviewed in the talk. Particular attention will be devoted to charge generation in organic semiconductors, where the high binding energy of electron-hole pairs hinders charge generation, and to recombination of carriers in inorganic amorphous materials, which in some cases does not fit into the general Onsager model.

Thin-film Photovoltaics
Sigurd Wagner, Princeton University, USA

Thin-film solar cells are attractive for their potentially low cost of materials and fabrication processes. When these advantages combine, developing a competitive thin-film photovoltaic technology requires substantially less investment than bulk silicon PV has needed. All solar cells function by photon-driven charge separation in energy and in space; these translate to voltage and current. Thin films of semiconductors deposited over large surface areas contain many defects, which hurt charge collection. I will examine thin-film silicon, CdTe, Cu(In,Ga)Se2, and organic cells for their ability to generate photocurrent, and also to identify cell-specific challenges. Then I will conclude with a personal outlook.

Thin Film Silicon Electronic Devices
Jin Jang, Kyung Hee University, Republic of Korea

I will talk about the fabrication, characterization of a-Si:H thin-films and their application to TFT and PIN diodes. The display application of TFTs, sensor and photovoltaic applications of PIN will be also touched on. In the 2nd part, I will discuss low temperature poly-Si (LTPS) on glass which is being used for high resolution displays such as the retina display and also for the Galaxy AMOLED. The crystallization techniques and electrical properties of LTPS TFTs will be discussed together with hot carrier and bias-stress effects. Some displays developed in ADRC will be also explained. The TFTs and AMOLED on flexible substrates will be added.

Chalcogenide Semiconductors: Fundamental Physics
Koichi Shimakawa, Gifu University, Japan

Chalcogenide glassy semiconductors (g-CGs) have unique electronic and optical properties among other disordered matter. After the introduction of well-established issues, e.g. electronic transport, optical properties, and the nature of defects, the following will be discussed: 1) unique features found in g-CGs, photoinduced effects, e.g. photodarkening, photoexpansion, and photoinduced defect creation, 2) the Meyer-Neldel (compensation) rule found in the carrier transport, and 3) recent topics of on electronic properties (0–THz–IR frequency range) in phase change materials. Overall physical properties on g-CGs can be well understood through studying the above issues.

Phase Change Memory Materials
John Robertson, University of Cambridge, UK

Phase change materials are generally GeSbTe alloys. They have a crystalline phase and an amorphous phase with almost the same energy, and they can change rapidly (<10 ns) between these phases on thermal activation. They were developed for rewritable DVDs by Panasonic, and are now being developed for phase change non-volatile electrical memories (PCRAM). They are poor glass formers. They are unusual because, unlike a-Si, they have very different bonding in their crystal and amorphous phases, although the nearest neighbor coordinations are no so different. This leads to a significant difference in refractive index, called optical contrast. The second difference is that they have vey different electrical resistivities, as used for PCRAM. I will review their atomic structures, models of bonding, electronic structures, phase change mechanism, and electrical properties. A further unusual feature is that these materials are "fragile glass formers", in which the viscosity and diffusion deviate from the Einstein relation near the glass transition, similar to poor glasses like metallic glasses or organic molecular glasses, and unlike a-SiO2 or a-Si.

Amorphous Oxide Semiconductor TFTs and Applications
Arokia Nathan, University of Cambridge, UK

Amorphous oxide semiconductor thin film transistors (TFTs) exhibit high transparency as well as high electron mobility even when fabricated at room temperature. These properties make oxide semiconductors a promising candidate for a new generation of applications where speed and transparency are essential requirements. While the oxide TFT shows a better dark-stability compared to amorphous silicon TFTs, it is optically unstable due to persistent photoconductivity believed to be due to ionization of oxygen vacancies located at the sub-gap. Although performance issues related to instability still remain, the attractive feature of the oxide TFT technology lies in process simplicity and relatively high device mobility. This tutorial will discuss the development of oxide TFTs for large area electronics with specific focus on display and imaging applications.

Optical and Electronic Properties of Organic Semiconductors
Robert A. Street, Palo Alto Research Center, USA

The tutorial will discuss the opto-electronic properties of organic semiconductors, primarily in the context of thin film transistors and solar cells. Topics will include carrier mobility, optical absorption and recombination mechanisms, as well as electronic structure and defects. The similarities and differences between the organic and inorganic disordered materials will be emphasized.

Organic Optoelectronic Devices
Hany Aziz, University of waterloo, Canada

The tutorial will build-up on the previous talk and discuss the principles of operation of a number of organic optoelectronic based devices, including light emitting diodes, photodetectors and other optoelectronic devices.

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