Browsing by Author "Nadtochiy, Andriy"

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A model for predicting the thermal conductivity of SiO2-Ge nanoparticle composites
(2015-01-01)
Kuryliuk, Vasyl
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Nadtochiy, Andriy
;
Korotchenkov, Oleg
;
Wang, Chin-Chi
;
Li, Pei-Wen
We present a simple theoretical model that predicts the thermal conductivity of SiO2 layers with embedded Ge quantum dots (QDs). Overall, the resulting nanoscale architecture comprising the structural relaxation in the SiO2 matrix, deviation in mass density of the QDs compared to the surrounding matrix and local strains associated with the dots are all likely to enhance phonon scattering and thus reduce the thermal conductivity in these systems. We have found that the conductivity reduction can be predicted by the dot-induced local elastic perturbations in SiO2. Our model is able to explain not only this large reduction but also the magnitude and temperature variation of the thermal conductivity with size and density of the dots. Within the error range, the theoretical calculations of the temperature-dependent thermal conductivity in different samples are in close agreement with the experimental measurements. Including the details of the strain fields in oxidized Si nanostructured layers is therefore essential for a better prediction of the heat pathways in on-chip thermoelectric devices and circuits.
Enhancing the Seebeck effect in Ge/Si through the combination of interfacial design features
(2019-11-08)
Nadtochiy, Andriy
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Kuryliuk, Vasyl
;
Strelchuk, Viktor
;
Korotchenkov, Oleg
;
Li, Pei-Wen
Due to their inherent physical properties, thin-film Si/SiGe heterostructures have specific thermal management applications in advanced integrated circuits and this in turn is essential not only to prevent a high local temperature and overheat inside the circuit, but also generate electricity through the Seebeck effect. Here, we were able to enhance the Seebeck effect in the germanium composite quantum dots (CQDs) embedded in silicon by increasing the number of thin silicon layers inside the dot (multi-fold CQD material). The Seebeck effect in the CQD structures and multi-layer boron atomic layer-doped SiGe epitaxial films was studied experimentally at temperatures in the range from 50 to 300 K and detailed calculations for the Seebeck coefficient employing different scattering mechanisms were made. Our results show that the Seebeck coefficient is enhanced up to approximate to 40% in a 3-fold CQD material with respect to 2-fold Ge/Si CQDs. This enhancement was precisely modeled by taking into account the scattering of phonons by inner boundaries and the carrier filtering by the CQD inclusions. Our model is also able to reproduce the observed temperature dependence of the Seebeck coefficient in the B atomic layer-doped SiGe fairly well. We expect that the phonon scattering techniques developed here could significantly improve the thermoelectric performance of Ge/Si materials through further optimization of the layer stacks inside the quantum dot and of the dopant concentrations.
Improving Photoelectric Energy Conversion by structuring Si Surfaces with Ge Quantum Dots
(2019-01-01)
Shmid, Volodymyr
;
Kuryliuk, Vasyl
;
Nadtochiy, Andriy
;
Korotchenkov, Oleg
;
Li, Pei-Wen
Structuring Si surfaces with Ge quantum dots can have a beneficial effect on the photovoltage (PV), increasing the PV magnitude and decay time. The origin of this behavior is intimately related to mechanical strains developed in the vicinity of the Ge/Si interface. The structuring is a promising means of avoiding the uncontrolled production of recombination centers and offering significant enhancement of the recombination lifetime due to carrier trapping in the dots. This work can open new opportunities for advanced photoelectric devices with recombination center free nanostructures.