Title:Silicon Based Germanium Tin Alloys: Extension of the Infrared Range
Speaker: Prof. Erich Kasper (Institut für Halbleitertechnik, Universit？t Stuttgart, Germany)
Venue:academic salon room, IOS,CAS
Time:PM15:00, Nov. 14, 2011
Abstract:Germanium tin( GeSn) is predicted to convert from an indirect semiconductor at low Sn contents to a direct one at higher Ge contents. The bandgap is lower than that of Ge , there by extending the spectral range beyond a wavelength of 1.55 μm. Single phase GeSn alloys are important for silicon based heterostructure devices as stressors for Ge channels and as candidates for direct/indirect band cross-over. Such alloys would allow superior Ge channel metal on insulator devices and optoelectronic infrared circuits on a Si substrate. Germanium tin (GeSn) is under equilibrium a two phase (Ge+Sn) system. Preparation of GeSn layers is possible at low growth temperatures. We discuss the challenges caused by the non-equilibrium growth and the limitations of low temperature epitaxy. Main challenges and limitations are the surface segregation, precipitations and defect accumulation in low temperature epitaxy. The problem of high lattice mismatch between Si and GeSn (> 4 %) can be solved using virtual substrates with strain relaxed Ge buffer layers. The lattice mismatch can be reduced to 1 % and below. Growth of pseudomorphic GeSn layers on Ge buffers/Si substrate was investigated. The samples were characterized by X-ray methods and Raman spectroscopy. High device process stability was achieved up to 600°C annealing and documented by Raman spectroscopy. Fabrication of a photodetector test device demonstrated feasibility for optoelectronic applications with extended infrared range. Light emitting diodes from low Sn content alloys confirmed the predicted red shift of the direct bandgap emission.
Biography: Erich Kasperreceived the Ph.D. degree in physics from the University of Graz, Graz, Austria, in 1971. His dissertation thesis concerned electrical properties of dislocations in silicon.He was active as a Scientist with the research laboratories of the companies Telefunken, AEG and Daimler-Benz. His main research concerned solid-state analysis by X-ray topography and electron microscopy, material synthesis by MBE, and semiconductor device preparation for microwave applications. From 1987 on, he was responsible for novel silicon devices and technology with Daimler-Benz Research, Ulm, Germany, with a main emphasis on SiGe/Si-based heterostructures for fast transistors (heterobipolar transistor-HBT, modulation doped field effect transistor MODFET) and opto-electronic transceivers (ultrathin superlattice).Since 1993, he has been with the University of Stuttgart, Stuttgart, Germany, as Professor of Electrotechnical Engineering and Head of the Institute of Semiconductor Engineering. His main interest is directed to silicon-based nanoelectronics, integration of millimeter-wave circuits, and SiGe/Si quantum-well devices. In 2008 he retired as Institute Head but retained with University of Stuttgart as Research Professor. He was appointed as Guest Professor at Huazhong University of Science and Technology(HUST), Wuhan, China in 2009, and he continues to lecture at the Montanuniversitaet in Leoben, Austria. Recent activities focus on exploitation of research results, on application of Ge/Si for photovoltaics and energy harvesting and on mm-wave imaging.