Professur für Opto- und Festkörperelektronik






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Atomic Scale Engineering Group



E. Nadimi - E. Nakhmedov - P. Plänitz - A. Mitin - A. Martinez - R. Janisch - C. Radehaus

Research Topics

Dielectrics for advanced CMOS technology

Our research includes ab initio modelling of gate materials, focussing on near and long term solutions for industrial applications. Modelling and evaluation steps are in progress including:
  • determination of bulk and interface structures
  • calculation of electronic band structures -including GW methods- and dielectric constants
  • simulation of defects and their influence
  • modelling thermal stability using classical and ab initio molecular dynamics
  • developing new transport models for the leakage current in CMOS structures

Prof. C. Radehaus

Classical Monte Carlo (CMC) and Classical Molecular Dynamics (CMD)

CMC and CMD are powerful tools for the modelling of materials, nanostructures and biomolecules. They are especially adequate to generate relaxed structures of complex systems where ab inito calculations would be impracticable, to model long term evolution, diffusion of atoms, or thermal stability. Refined classical potentials could even model some typical reactions in systems with few atomic species.

Alberto Martinez

Electronic structure of crystalline and amorphous SiOxNy materials

We perform ab initio calculations of the electronic properties for different nitrogen concentration. The simulation results include total energy, band structure, density of states, the electron density distribution in space, effective mass and dielectric function. Beside the crystalline materials we calculate different amorphous structure models for low nitrogen content.

Philipp Plänitz
Mohammed Bouhassoune

Si-Insulator Interfaces

An example of a well known but still unresolved problem in modern semiconductor devices is the leakage current at the silicon – silicon dioxide interface in MOSFETs. It is determined by the electronic density of states (DOS) at the interface. Our goal is to engineer this DOS by manipulating the atomic structure and by choosing the right dopants and dopant concentrations. For our studies we use Car-Parinello Molecular Dynamics and Density Functional total energy and electronic structure calculations.

Rebecca Janisch

Ab initio modelling of defect structures in semiconductors and insulators

Our investigations of defects in dielectrics are motivated by academic interest for the study of defects influence on the physical properties of materials as well as by the industrial interest for the study of microelectronics devices degradation. According to the modern understanding, the stress-induced leakage current (SILC) across the oxide of MOSFETs flows through percolation paths of defects. We use DFT based ab-initio methods to model the defect interactions, formation of the percolation path, diffusion of defects in insulators, etc.

Enver Nakhmedov

Models for leakage current in MOS structures

In the past decade, shrinking the transistor sizes has been used as a main approach to achieve faster devices. An enormous high value of leakage current across the ultra-thin gate oxide sets a barrier for more scaling. We investigate analytical and numerical models for studying the influence of material properties, correlation effects and defects on leakage current. Our current study focuses on the application of non-equilibrium Green’s function approach and related tools to calculate leakage current even at the atomic level.

Ebrahim Nadimi

Recent publications of group members
Study of direct tunnelling current oscillations in ultrathin gate dielectrics, E. P. Nakhmedov, C. Radehaus, and K. Wieczorek, J. Appl. Phys., 97, 064107 (2005)

Quantum mechanical study of the direct tunnelling current in metal-oxide-semiconductor structures, E. P. Nakhmedov, K. Wieczorek, H. Burghardt, and C. Radehaus, J. Appl. Phys.98, (2005)

Transition metal-doped TiO2 and ZnO - present status of the field, Rebecca Janisch, Priya Gopal, and Nicola A. Spaldin, J. Phys.: Condens. Matter, 17, R657-689, (2005)

Understanding catalysed growth of single-wall carbon nanotubes, J. Zhao, A. Martinez-Limia, and P. B. Balbuena, Nanotechnology, 16, S575-S581, (2005)

Properties of a nondispersive Mn-3d band in (GaxMn1-x)As, Ernst A, Sandratskii LM, Bouhassoune M, Henk J, Bruno P, Verhandlungen der Deutschen Physikalischen Gesellschaft, 40, 245 (2005)

Lagrange Type Iterative Methods for Calculations of Extreme Eigenvalues of Large Symmetric Matrices, A. V. Mitin, submitted to SIAM J. Scientific Computing

Structural and electronic properties of dangling bonds free nitridated Silicon Dioxide, P. Plänitz, A. Martinez-Limia, C. Radehaus, in preparation

Simulation of the direct tunneling current in Metal- Oxide- Semiconductor capacitor with half- opened boundaries, E. Nadimi and C. Radehaus, E.P. Nakhmedov, and K. Wieczorek, in preparation

Ferromagnetic Superexchange in Co doped TiO2, Rebecca Janisch and Nicola A. Spaldin, in preparation

Accurate Calculation of Dissociation Energies of He2 and Be2 Molecules by MRCI Method, A. V. Mitin, in preparation

Two-Component Relativistic DFT Method, A. V. Mitin, Ch. Van Wüllen, in preparation

Effect of static electric field on the HF band structure of a guanine stack, Martinez, A; Bogar, F.; Otto, P.; Ladik, J., Int. J. Quantum Chem., 99, 833-840 (2004)

Crystalline structure and lithium-ion channel formation in self-assembled di-lithium phthalocyanine: Theory and experiments, Zhang, YC; Alonso, PR; Martinez-Limia, A; Scanlon, LG; Balbuena, PB, J. Phys. Chem. B, 108, 4659-4668 (2004)

Dynamic (hyper)polarizability calculations for polymers with linear and cyclic p-conjugated elementary cells, Otto, P; Piris, M; Martinez, A; Ladik, J, Synthetic Metals, 141, 277-280 (2004)

Natural orbital functional approach: Calculation of dielectric properties in molecules, Piris, M; Martinez, A; Otto, P, Int. J. Quantum Chem., 97 ,827-831 (2004)

An Improved 6-31G* Basis Set for Atoms Ga through Kr, A. V. Mitin, J. Baker, and P. Pulay, J. Chem. Phys., 118, 7775-7782 (2003)

Eficient Parallel Conventional and Semi-Direct Hartree-Fock and DFT Methhods with Data Compression, A. V. Mitin, J. Baker, K. Wolinski, and P. Pulay, J. Comput. Chem., 24, 154-160, (2003)

Temperature dependence of the confined exciton states in CdTe/Cd1-xZnxTe cylindrical quantum dots, El Moussaouy A, Bria D, Nougaoui A, Charrour R, Bouhassoune M, Physics of Low-Dimensional Structures 11, 57-69, (2003)

Exciton-phonon coupled states in CdTe/Cd1-xZnxTe quantum dots, El Moussaouy A, Bria D, Nougaoui A, Charrour R, Bouhassoune M, J. Appl. Phys. 93, 2906-2911 (2003)

Polaronic and magnetic field effects on the binding energy of an exciton in a quantum well wire, Bouhassoune M, Charrour R, Fliyou M, Bria D, Nougaoui A., J. Appl. Phys. 91, 232-236 (2002)

Large Scale Hartree-Fock Calculations. Compression of Two-Electron Integrals and their Indices, A. V. Mitin, J. Molec. Structure (Theochem), 592, 115-121 (2002)