| CZECH NANO TEAM | Physics of Nanostructures and Nanotechnologies

• Correlation of microstructure (studied by Atomic Force Microscopy - AFM) and local electronic properties with nm lateral resolution. Identification of Si nanocrystals in amorphous background.

• Preparation of polycrystalline Si by field-induced crystallization of a-Si:H at room temperature.
• The supervisor of 7 successful diploma theses, 4 PhD and CSc theses.

Publications:

Author or co-author of more than 200 scientific publications (more than 110 were published in international journals) to which more than 1050 references appeared in the literature. Amongst these there are joint papers with the University of Marburg, Tokyo Institute of Technology, FTI Leningrad, University of Neuchatel, University of Vilnius, Siemens Central Res. Lab.-Munich, University of Stuttgart, Max-Planck-Institute in Stuttgart, Brown University - Providence, Xerox PARC -Palo Alto, ENEA-Naples, 10 invited papers and also invited contributions to three books.

Selected study stays abroad:

• In 1977 awarded by 4 month's fellowship by Cambridge University (Prof. E.A. Davis, Cavendish Lab.)

• In 1988 invited by Prof. F. Koch for 1 month's stay at Technical University Munich-Garching

• In 1990 invited by Prof. W.H. Bloss for 6 month's stay at University of Stuttgart

• In 1993 invited by Prof. I. Shimizu as a visiting professor for 3 months to Tokyo Inst. of Technology

• In 1995 invited by Prof. Kazunobu Tanaka from JRCAT (Tsukuba) for 1 month's stay.

Selected solved projects:

• EC-PECO-CT 925034(1992-94) "Accelerated test and improvement of stability of a-Si:H solar cells"

• EC-PECO-CT 927839(1993-96) "Non-conventional preparation of light emitting silicon, its transport and optical properties"

• NEDO-Intern. collaboration grant (1996-98) "Development of amorphous field effect solar cells based on a-Si:H"

• NEDO-Contract (1997-2001)"The search for new thin film tandem photovoltaic cells based on a-Si:H"

Selected related publications from last 5 years:

• B. Rezek, J. Stuchlík, A. Fejfar, J. Kočka: Local characterization of electronic transport in microcrystalline silicon thin films with submicron resolution, Appl. Phys. Lett. 74, 1475 - 1477 (1999)

• V. Švrček, I. Pelant, J. Kočka, P. Fojtík, B. Rezek, H. Stuchlíková, A. Fejfar, J.Stuchlík, Poruba and J.Toušek: Transport Anisotropy in Microcrystalline Silicon Studied by Measurement of Ambipolar Diffusion Length, J. Appl. Phys. 89, 1800-1805 (2001)

• B. Rezek, J. Stuchlík, A. Fejfar, J. Kočka: Microcrystalline silicon thin films studied by atomic force microscopy with electrical current detection, J. Appl. Phys. 92, 587-593 (2002)

• P. Fojtík, K. Dohnalová, T. Mates, J. Stuchlík, I. Gregora, J. Chval, A. Fejfar, J.Kočka and I. Pelant:Rapid crystallization of amorphous silicon at room temperature,Phil. Mag. B 82, 1785-1793 (2002)

• J. Kočka, A. Fejfar, H. Stuchlíková, J. Stuchlík, P. Fojtík, T. Mates, B. Rezek, K. Luterová, V. Švrček, I. Pelant: Basic features of transport in microcrystalline silicon, Solar Energy Materials &Solar Cells 78,493-512 (2003)

Group members:

Jan Kočka, Ivan Pelant, Kateřina Luterová, Petr Fojtík, Kateřina Dohnalová, Antonín Fejfar, Vlado Švrček, Jan Valenta and Petr Malý (FMF-ChU)

Main Research Subjects:

The first subject is preparation and study of amorphous and nano/microcrystalline silicon (a-Si:H, µc-Si:H).While these are used for large area production of flat displays and solar cells the basic properties are not fully understood. Namely for µc-Si:H the macroscopic properties like crystallinity and electron transport properties are very sensitive to tiny changes of complex microstructure in nanometer scale (Si nanograins, grain boundaries).The aim is to develop a predictive model connecting the µc-Si:H growth, resulting microstructure and macroscopic physical properties.

The second subject is experimental study of optical and photoelectric properties of low-dimensional structures, predominantly nanocrystals of silicon and of II-VI semiconductors. Among them are first of all photoluminescence, ultrafast optical processes (in pico and femtosecond range), electroluminescence and active optical waveguides made of nanocrystals. Various types of samples are being prepared, also in cooperation with research institutions abroad (Universite Louis Pasteur Strasbourg, France; University of Canberra, Australia etc.) The question of whether it is possible to achieve stimulated emission in silicon nanocrystals and to design silicon laser in the visible region (which is absolutely impossible with bulk silicon) is one of pursued hot topics. Positive answer would mean creation of a new generation of information technologies, e.g. computers based on photonic rather than electronic operation mode.

Selected Specific Equipment:

Quick oxidation of silicon complicates the study of surface topography and sometime prevents the study of local transport properties. That is why we have built plasma enhanced glow discharge (13-100MHz) technology, connected directly to Omicron AFM/STM variable temperature UHV system. We can in-situ prepare a-Si:H, µc-Si:H and to do hydrogen (or other gas) surface treatment. For identification of growing crystallites we can use local current probes able to test the electric conductivity of composites containing semiconductor nano/microcrystals with high lateral resolution (of the order of 10 nm).

Another specific equipment connected to Omicron AFM/STM variable temperature UHV system is a photon detection system, designed to record light emission from nanocrystals under excitation by tunneling electrons in STM microscope. This will facilitate the investigation of microscopic nature of recombination processes. Similar experimental set-up, aimed at studying luminescent properties of single semiconductor nanocrystals under optical excitation, is also available. To study ultrafast optical processes, a Ti: Sapphire laser system (Spectra Physics) emitting 60 fs pulses and a Nd:YAG laser system with nonlinear transformation of wavelengths and 30 ps pulses are at hand.

Additional recent selected publications by group members:

• G. Juška, K. Arlauskas, M. Viliunas, J. Kočka: Extraction Current Transients: New Method of study of Charge Transport in Microcrystalline Silicon, Phys. Rev. Lett. 84, 4946 (2000)

• J. Valenta, J. Dian, K. Luterová, P. Knápek, I. Pelant, M. Nikl, D. Muller, J.J. Grob, J.-L. Rehspringer and B. Hönerlage: Temperature Behaviour of Optical Properties of Si+--implanted SiO2, Europ. Phys. J. D 8, 395-398 (2000)

• K. Luterová, I. Pelant, P. Fojtík, M. Nikl, I. Gregora, J. Kočka, J. Dian, J. Valenta, P. Malý, J. Kudrna, J. Štěpánek, A. Poruba and P. Horváth: Visible Photoluminescence and Electroluminescence in Wide Band Gap Hydrogenated Amorphous Silicon, Philosophical Magazine B 80, 1811-1832 (2000)

• J. Kudrna, F. Trojánek, P. Malý, I. Pelant: Carrier diffusion in microcrystalline silicon studied by the picosecond laser induced grating technique, Appl. Phys.Lett 79, 626-628 (2001)

• P. Malý, F. Trojánek, T. Miyoshi, K. Yamanaka, K. Luterová, I. Pelant, P. Nemec: Ultrafast carrier dynamics in CdSe nanocrystalline films on crystalline silicon substrates, Thin Solid Films 403-404 462-466 (2002)

• K. Luterová, I. Pelant, I. Mikulskas, R. Tomasiunas, D. Muller, J.-J. Grob, J.-L. Rehspringer and B. Hönerlage: Stimulated emission in blue-emitting Si+-implanted SiO2 films?, J. Appl. Phys. 91, 2896-2900 (2002)

• J. Valenta, I. Pelant and J. Linnros: Waveguiding effects in the measurement of optical gain in a layer of Si nanocrystals, Appl. Phys. Lett. 81, 1396-1398 (2002)

• J. Valenta, I. Pelant, K. Luterová, R. Tomasiunas, S. Cheylan, R.G. Elliman, J. Linnros, B.Hőnerlage: Active planar optical waveguide made from luminescent silicon nanocrystals, Appl. Phys. Lett. 82, 955-957. (2003)