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TU Dresden » Faculty of Mechanical Science and Engineering » Institute for Materials Science » Chair of Materials Science and Nanotechnology

Friday, 26 June 2009
(at 14:00 in room 115, Hallwachsstr. 3)
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Nanocrystalline materials - optimization of thin film properties

Johannes Heitmann


Nanocrystalline materials play a major role in semiconductor research and development. Si nanocrystals are discussed as absorber material for solar cells of the third generation [1]. Semiconductor industries made a step towards nanocrystalline dielectrics for MIM capacitors in DRAM and rf applications [2], as well as for gate dielectric for sub 45 nm devices. Nanocystalline glases as host material for rare earth elements enhance the efficiency of up- and downconversion processes in photovoltaic applications [3]. These material properties of the nanostructures like enhanced electron-hole interactions, resonant energy transfer to rare earth elements, stabilization of proper crystalline phases are only a few which start to become more and more important. One of the biggest problems in nanocrystal synthesis is to enable a precise size control of the fabricated structures [4]. In this talk size and crystalline phase control by the supperlattice approach and by doping will be shown. Two main examples will be discussed: 1) Si nanocrystal synthesis by SiO/SiO2 superlattices which result in an array of well passivated monodisperse nanocrystals. The influence of the nanocrystal size on confinement energy, increase in direct transition probability and the energy transfer to Erbium is investigated in detail. 2) Using a similar superlattice approach to stabilize higher k phases in HfO2 and ZrO2 based dielectrics and compare this approach with the stabilization effect by doping with Al2O3 and SiO2. In this case the higher amount of surface energy lead to the stabilization of the tetragonal phase in contrast to the monoclinic phase which is the stable phase for the bulk materials. The effect of doping and interlayers on the electrical performance like leakage current and dielectric relaxation will be discussed. For both material systems the size control of the nanocrystallites by thin film deposition techniques is mandatory to enable certain material properties and to make a detailed optical investigation possible, specially for the indirect semiconductor Silicon.

[1] G. Conibeer, M. Green, R. Corkish, Y. Cho, E. Cho, C. Jiang, T. Fangsuwannarak, E. Pink, Y. Huang, T. Puzzer, T. Trupke, B. Richards, A. Shalav and K. Lin, Silicon nanostructures for third generation photovoltaic solar cells, Thin Solid Films 511-512 (2006), 654-662.
[2] J. Heitmann, A. Avellan, T. Boescke, E. Erben, B. Hintze, S. Jakschik, S. Kudelka, and U. Schroeder, HfAlO and HfSiO Based Dielectrics for Future DRAM Application, ECS. Trans. 2 (2006) 217.
[3] S. Schweizer, L.W. Hobbs, M. Secu, J.-M. Spaeth, A. Edgar, G.V.M. Williams, Photostimulated luminescence from fluorochlorozirconate glass ceramics and the effect of crystallite size, J. Appl. Phys. 97 (2005) 083522.
[4] J. Heitmann, F. Mueller, M. Zacharias, and U. Goesele, Silicon nanocrystals: Size matters. Advanced Materials 17(7) (2005) 795-803.

Brief Bio:

Johannes Heitmann holds a diploma (Univ. of Leipzig 1998) and a Ph.D. in Physics (MPI fuer Mikrostrukturphysik Halle 2003). During this time he had half a year of work experience abroad at the Micro Analytic Research Center, School of Physics, Unviersity of Melbourne, Australia. Later he worked as Senior Engineer for Material Development at Infineon / Qimonda AG Dresden (2004-2009). His research interests are in the field of nanocrystalline materials for optical and electrical applications.

Invited by G. Cuniberti (nanoSeminar)

last modified: 2021.10.02 Sat
author: webadmin