M. Povolotskyi

Elasticity theory of pseudomorphic heterostructures grown on substrates of arbitrary thickness

A theoretical model for lattice mismatched pseudomorphically grown heterostructure, which is based on continuum elasticity theory is described. Two distinct types of coherently grown structures are considered, namely, those grown on a thick substrate and these grown on a freestanding one. Special cases of structures that are homogeneous or periodic in some directions are considered. The theory can be applied for an arbitrary crystallographic direction of the heterostructure growth. The model has been applied to AlN∕GaN nanocolumn and GaAs∕InAs heterostructure. Calculation of strain induced shape deformation is shown.

Full-Band Tunneling in High-

In this paper, we investigate the tunneling properties of ZrO2 and HfO2 high-k oxides, by applying quantum mechanical methods that include the full-band structure of Si and oxide materials. Semiempirical sp3s*d tight-binding parameters have been determined to reproduce ab-initio band dispersions. Transmission coefficients and tunneling currents have been calculated for Si/ZrO2/Si and Si/HfO2/Si MOS structures, showing a very low gate leakage current in comparison to SiO2-based structures with the same equivalent oxide thickness. The complex band structures of ZrO2 and HfO2 have been calculated and used to develop an energy-dependent effective tunneling mass model. We show that effective mass calculations based on this model yield tunneling currents in close agreement with full-band results.

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Due to the downscaling of semiconductor device dimensions and the emergence of new devices based on nanostructures, CNTs and molecules, the classical device simulation approach based on semi-classical transport theories needs to be extended towards a quantum mechanical description. We present a simulation environment designed for multiscale and multiphysics simulation of electronic and optoelectronic devices with the final aim of coupling classical with atomistic simulation approaches.

Oxide MOS Structures

We present the TiberCAD multiscale device simulation software. The scope of the project is a full description of charge transport and optoelectronic properties of devices with embedded active regions of nanometer-scale. We show simulations of a GaN LED that requires modeling of strain, transport of electrons, holes and excitons and device heating.

TiberCAD: Towards multiscale simulation of optoelectronic devices

Significant optical nonlinearity has been found in InGaAs (311)A sidewall quantum wires by means of time resolved photoluminescence measurements. A strong reverse quantum confined Stark effect has been observed and attributed to the dynamical screening of both the internal piezoelectric field and the Coulomb interaction between carriers. The time evolution of the quantum wire emission has been reproduced by means of self-consistent calculations that take into account excitonic effects, strain, and induced piezoelectric charges.

Multiscale Simulation of Electronic and Optoelectronic Devices with TiberCAD

Calculations of optoelectronic properties of a GaN quantum dot embedded in an AlGaN nanocolumn are presented, using the TiberCAD simulator. The calculations emphasize the role of the growth direction in determining the quantum efficiency of such light emitting devices. Multiband kldrp is used, with corrections from drift diffusion and strain calculations. Results are discussed using an empirical tight binding method, with the same macroscopic corrections as for kldrp, implemented in TiberCAD framework itself.

Dynamical nonlinearity in strained InGaAs (311)A sidewall quantum wires

We report on a multiscale simulation approach that includes both macroscopic drift-diffusion current model and atomistic quantum tunneling model. The models are solved together in a self-consistent way inside a single simulation package. We compare the high-K gates based on HfO2 and ZrO2 with a SiO2 gate of the same equivalent thickness and show the effect of the tunneling current on transistor performance.

Simulations of Optical Properties of a GaN Quantum Dot Embedded in a AlGaN Nanocolumn within a Mixed FEM/atomistic Method

Abstract High- κ oxides such as ZrO 2 and HfO 2 have attracted great interest, due to their physical properties, suitable to replacement of SiO 2 as gate dielectric materials. In this work, we investigate the tunneling properties of ZrO 2 and HfO 2 high- κ oxides, by applying quantum mechanical methods that include the full-band structure of Si and oxide materials. Semiempirical sp 3 s∗d tight-binding parameters have been determined to reproduce ab initio band dispersions. Transmission coefficients and tunneling current have been calculated for Si/ZrO 2 /Si and Si/HfO 2 /Si MOS structures, showing a very low gate leakage current in comparison to SiO 2 -based structures with equivalent oxide thickness.

Multiscale Atomistic Simulations of High-k MOSFETs

Quantum dot (QD) systems based on III-nitride have recently shown to be very promising nanostructures for high-quality light emitters. In this work, electronic and transport properties of AlN/GaN QDs are investigated by means of the TIBERCAD software tool, which allows both a macroscopic and an atomistic approach, with the final aim to couple them in a multiscale simulation environment.

Full-band tunneling in high-κ dielectric MOS structures

Abstract Using quantum mechanical methods that include the full-band structure, we study two quantum mechanical phenomena that occur in MOS transistors: ultrathin oxide tunneling and inversion layer quantization. We obtain good agreement between calculated and measured tunneling current densities for a n-poly Si/SiO2/p-Si capacitor under negative gate bias. In addition, we find that for typical inversion layer fields, quantization energies