scholarly journals Computational Study of In-Plane Phonon Transport in Si Thin Films

2014 ◽  
Vol 4 (1) ◽  
Author(s):  
Xinjiang Wang ◽  
Baoling Huang
Keyword(s):  
Thin Films ◽  
Thermal Transport ◽  
Computational Study ◽  
Isotope Effects ◽  
Phonon Transport ◽  
Phonon Confinement ◽  
Phonon Modes ◽  
Scattering Rate ◽  
Si Films ◽  
Thermal Conductivities

Abstract We have systematically investigated the in-plane thermal transport in Si thin films using an approach based on the first-principles calculations and lattice dynamics. The effects of phonon mode depletion induced by the phonon confinement and the corresponding variation in interphonon scattering, which may be important for the thermal conductivities of ultra-thin films but are often neglected in precedent studies, are considered in this study. The in-plane thermal conductivities of Si thin films with different thicknesses have been predicted over a temperature range from 80 K to 800 K and excellent agreements with experimental results are found. The validities of adopting the bulk phonon properties and gray approximation of surface specularity in thin film studies have been clarified. It is found that in ultra-thin films, while the phonon depletion will reduce the thermal conductivity of Si thin films, its effect is largely offset by the reduction in the interphonon scattering rate. The contributions of different phonon modes to the thermal transport and isotope effects in Si films with different thicknesses under various temperatures are also analyzed.

Thermal transport in beta-gallium oxide thin-film using non-gray Boltzmann transport equation

2021 ◽  
Author(s):  
Nitish Kumar ◽  
Matthew Barry ◽  
Satish Kumar
Keyword(s):  
Thin Films ◽  
Temperature Distribution ◽  
Energy Dissipation ◽  
Thermal Transport ◽  
Energy Exchange ◽  
Domain Size ◽  
Phonon Transport ◽  
Boltzmann Transport ◽  
Phonon Modes ◽  
Fourier Model

Abstract Phonon transport  in β-Ga2O3 thin films and metal–oxide field effect transistors (MESFETs) are investigated using non-gray Boltzmann transport equations (BTE) to decipher the effect of  ballistic-diffusive phonon transport. The effects of domain size, and  energy dissipation to various phonon modes and subsequent phonon-phonon energy exchange on the thermal transport and temperature distribution is investigated using non-gray BTE. Our analysis deciphered that domain size plays a major role in thermal transport in β-Ga2O3 but energy dissipation to various phonon modes and subsequent phonon-phonon energy exchange does not affect the temperature field significantly.   Phonon transport in β-Ga2O3 MESFETs on diamond substrate is investigated using coupled non-gray BTE and Fourier model. It is established that the ballistic effects need to be considered for devices with β-Ga2O3 layer thickness less than 1 µm. A non-gray phonon BTE model should be used near hotspot in the thin β-Ga2O3 layer as the Fourier model may not give accurate temperature distribution. The results from this work will help in understanding the mechanism of phonon transport in the β-Ga2O3 thin films and energy efficient design of its FETs.

Four-Probe Measurement of Thermal Transport in Suspended Few-Layer Graphene With Polymer Residue

2019 ◽  
Vol 141 (6) ◽  
Author(s):  
Eric Ou ◽  
Xun Li ◽  
Sangyeop Lee ◽  
Kenji Watanabe ◽  
Takashi Taniguchi ◽  
...  
Keyword(s):  
Thermal Resistance ◽  
Thermal Transport ◽  
Thermal Contact ◽  
Experimental Studies ◽  
Phonon Transport ◽  
Contact Thermal Resistance ◽  
Layer Graphene ◽  
Scattering Rate ◽  
Transport Measurements ◽  
Polymeric Residue

The presence of unknown thermal contact thermal resistance has limited prior two-probe thermal transport measurements of suspended graphene samples. Here, we report four-probe thermal transport measurements of suspended seven-layer graphene. By isolating the thermal contact resistance, we are able to attribute the observed reduced thermal conductivity primarily to polymeric residue on the sample instead of the contact thermal resistance, which resulted in ambiguity in the prior experimental studies of the effect of polymer reside. The extrinsic scattering rate due to the polymer residue is extracted from the measurement results based on a solution of the Peierls-Boltzmann phonon transport equation.

scholarly journals Thermal transport in nanocrystalline Si and SiGe by ab initio based Monte Carlo simulation

2017 ◽  
Vol 7 (1) ◽  
Author(s):  
Lina Yang ◽  
Austin J. Minnich
Keyword(s):  
Thermal Conductivity ◽  
Monte Carlo ◽  
Ab Initio ◽  
Grain Boundaries ◽  
Thermal Transport ◽  
Phonon Scattering ◽  
Phonon Dispersion ◽  
Computational Study ◽  
Phonon Transport ◽  
Nanocrystalline Si

Abstract Nanocrystalline thermoelectric materials based on Si have long been of interest because Si is earth-abundant, inexpensive, and non-toxic. However, a poor understanding of phonon grain boundary scattering and its effect on thermal conductivity has impeded efforts to improve the thermoelectric figure of merit. Here, we report an ab-initio based computational study of thermal transport in nanocrystalline Si-based materials using a variance-reduced Monte Carlo method with the full phonon dispersion and intrinsic lifetimes from first-principles as input. By fitting the transmission profile of grain boundaries, we obtain excellent agreement with experimental thermal conductivity of nanocrystalline Si [Wang et al. Nano Letters 11, 2206 (2011)]. Based on these calculations, we examine phonon transport in nanocrystalline SiGe alloys with ab-initio electron-phonon scattering rates. Our calculations show that low energy phonons still transport substantial amounts of heat in these materials, despite scattering by electron-phonon interactions, due to the high transmission of phonons at grain boundaries, and thus improvements in ZT are still possible by disrupting these modes. This work demonstrates the important insights into phonon transport that can be obtained using ab-initio based Monte Carlo simulations in complex nanostructured materials.

DSMC Scheme for Phonon Transport in Solid Thin Films

2012 ◽  
Vol 134 (5) ◽  
Author(s):  
Mitsuhiro Matsumoto ◽  
Masaya Okano ◽  
Yusuke Masao
Keyword(s):  
Thin Films ◽  
Input Parameter ◽  
Direct Simulation Monte Carlo ◽  
Phonon Transport ◽  
Boltzmann Transport ◽  
Phonon Modes ◽  
Phonon Dynamics ◽  
Solid Thin Films ◽  
Simulation Monte Carlo ◽  
Phonon Model

Analysis of phonon dynamics based on a linearized Boltzmann transport equation is widely used for thermal analysis of solid thin films, but couplings among various phonon modes appear in some situations. We propose a direct simulation Monte Carlo (DSMC) scheme to simulate the phonon gas starting without the conventional linearization approximation. This requires no relaxation time as an input parameter, and we can investigate the couplings among phonons with different modes. A prototype code based on a simple phonon model was developed, and energy flux was evaluated for thin films of various thickness as a test calculation.

Thermal Conductivity of Phonon Modes in Graphene Nanoribbon at Localized High Heating

2015 ◽  
Author(s):  
Tatiana Zolotoukhina
Keyword(s):  
Thermal Conductivity ◽  
Thermal Transport ◽  
Single Layer ◽  
Phonon Transport ◽  
Graphene Nanoribbon ◽  
Single Layer Graphene ◽  
Quasi Equilibrium ◽  
Phonon Modes ◽  
Limited Region ◽  
Small Areas

The spectral components of the phonon transport in the locally thermally excited graphene samples were studied by molecular dynamics (MD) method. In order to be able to select and analyze separate phonon modes in the time of propagation, the transient Green-Kubo approach to the definitions of density of states (DOS) and thermal conductivity was tested in quasi-equilibrium regimes for limited region of the graphene sample studied. Propagation of single modes at the background of diffusional phonon distribution and energy decay of such modes are studied by calculation of the DOS and dispersion relations, their dependence on the heating condition and temperature is studied. Similar conditions can be generated at localized heating of small areas of graphene structures in electronic devices. In transient regime, many issues of thermal transport evaluation still remain not sufficiently tested, especially phonon dynamics. Thermal conductivity of graphene samples related to transport of separate phonon modes is still not completely investigated, however, recent result give indication on the difference in the contribution of phonon modes. In the study, we consider mostly high temperature transport modes that are generated at the heated spot in order to be able to define their velocities and lifetimes in the limit of transient MD sampling. The single-layer graphene nanoribbon of 150 nm to 40 nm was relaxed and prepared in equilibrium in zigzag and armchair orientations. REBO potential for graphene was utilized. Our calculation has shown that at the heating to high temperatures of 1000K and higher, the G mode of graphene remains stationary and has a minimal contribution into thermal transport by coherent modes. The coherent phonon mode or modes that contribute the most into thermal transport were confined in the vicinity of 30 THz and can possibly be attributed to the D modes of graphene.

Thermal Conductivity Anisotropy in Phonon Transport of Bi2Te3/Bi0.5Sb1.5Te3 Superlattice Film

2020 ◽  
Vol 15 (4) ◽  
pp. 463-467
Author(s):  
Soo-Young Kang ◽  
No-Won Park ◽  
Won-Yong Lee ◽  
Min-Sung Kang ◽  
Gil-Sung Kim ◽  
...  
Keyword(s):  
Thin Films ◽  
Thermal Conductivity ◽  
Electron Scattering ◽  
Phonon Scattering ◽  
Phonon Transport ◽  
Temperature Dependent ◽  
Conductivity Anisotropy ◽  
Large Anisotropy ◽  
Temperature Dependent Thermal Conductivity ◽  
Thermal Conductivities

Nanoscale superlattice thin films generally exhibit larger phonon and electron scattering at the interface in the direction of the cross-plane of the samples. Therefore, it is very important to further detailed study of especially phonon transport of the superlattice films. Here, we report temperature dependent thermal conductivity anisotropy in phonon transport of Bi2 Te3 /Bi0.5 Sb1.5 Te3 superlattice thin films at 200–500 K. Thermal conductivity of these thin films for in- and cross-plane thermal conductivities were determined to be approximately 0.74 and 0.4 W m–1 K–1 at 200–500 K, respectively, clearly indicating ∼185% suppression in- and cross-plane thermal conductivities of the superlattice thin films with a large anisotropic behavior. Such large anisotropy in the thermal conductivity can be attributed to enhanced phonon scattering occurring at the interface of the Bi2Te3 and Bi0.5Sb1.5Te3 layer.

Computational Study of Thermal Transport in Nanowire-Graphene Thin Films

2018 ◽  
Vol 17 (4) ◽  
pp. 829-836 ◽  
Author(s):  
Man Prakash Gupta ◽  
Nitish Kumar ◽  
Satish Kumar
Keyword(s):  
Thin Films ◽  
Thermal Transport ◽  
Computational Study

Semiconductor Nanostructure Design for Thermoelectric Property Control

2019 ◽  
Vol 18 (03n04) ◽  
pp. 1940036 ◽  
Author(s):  
Y. Nakamura ◽  
T. Ishibe ◽  
T. Taniguchi ◽  
T. Terada ◽  
R. Hosoda ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
High Performance ◽  
Carrier Transport ◽  
Phonon Scattering ◽  
Phonon Transport ◽  
Phonon Confinement ◽  
Semiconductor Nanostructure ◽  
Si Nanocrystals ◽  
Si Films ◽  
Property Control

We present the methodologies for developing high-performance thermoelectric materials using nanostructured interfaces by reviewing our three studies and giving the new aspect of nanostructuring results. (1) Connected Si nanocrystals exhibited ultrasmall thermal conductivity. The drastic thermal conductivity reduction was brought by phonon confinement and phonon scattering. Here, we present discussion about the new aspect for phonon transport: not only nanocrystal size but also shape can contribute to thermal conductivity reduction. (2) Si films including Ge nanocrystals demonstrated that phonon and carrier conductions were independently controlled in the films, where carriers were easily transported through the interfaces between Si and Ge, while phonons could be effectively scattered at the interfaces. (3) Embedded-ZnO nanowire structure demonstrated the simultaneous realization of power factor increase and thermal conductivity reduction. The [Formula: see text] increase was caused by the interface-dominated carrier transport. The nanowire interfaces also worked as phonon scatterers, resulting in the thermal conductivity reduction.

An overview of phonon-based heat conduction models and their solution

2016 ◽  
Vol 26 (3/4) ◽  
pp. 916-949 ◽  
Author(s):  
V.M Wheeler ◽  
K K Tamma
Keyword(s):  
Heat Transfer ◽  
Thin Films ◽  
Heat Conduction ◽  
Thermal Transport ◽  
Phonon Transport ◽  
Random Motion ◽  
Comprehensive Overview ◽  
Content Type ◽  
The Subject ◽  
Numerical Discretization

Purpose – The purpose of this paper is to provide an overview and some recent advances in the models, analysis and simulation of thermal transport of phonons as related to the field of microscale/macroscale heat conduction in solids. The efforts focus upon a fairly comprehensive overview of the subject matter from a unified standpoint highlighting the various approximations inherent in the thermal models. Subsequently, the numerical formulations and illustrations using the current state-of-the-art are provided. Design/methodology/approach – This paper is dedicated to the approximate solution to the relaxation time phonon Boltzmann equation (BE). While original contributions are pointed out and addressed appropriately, the efforts and contributions will be focussed on a relatively complete overview highlighting the field from one unified standpoint and clearly stating all assumptions that go into the approximations inherent to existing models. The contents will be divided as follows: In the first section the authors will give an overview of semi-classical phonon transport physics. Then the authors will discuss the equation of phonon radiative transport (EPRT) and its approximations—the ballistic-diffusive approximation (BDA) and the new heat equation (NHE). Next the authors derive and discuss the C-F model. A numerical discretization method valid for all models is then presented followed by results to numerical simulations and discussion. Findings – From a unified treatment based on the introduction of an energy distribution function, the authors have derived the EPRT and its two well-known approximations: BDA and NHE. For completeness and to provide a vehicle for a general numerical discretization approach, the authors have also included analysis of the C-F model and the parabolic and hyperbolic descriptions of heat transfer along with it. The approximation of angular dependence of phonons in radiation-like descriptions of transport has been given special attention. The assumption of isotropy was found to be of paramount importance in the formulation of position space models for phononic thermal transport. For the thin film problem considered here, the NHE along with the proper boundary condition appears to be the best choice to approximate the phonon BE. Not only does it provide predictions that are in excellent agreement with EPRT, it does not require the discretization of phase space making it far more computationally efficient. Originality/value – The authors hope this work will help dispel the idea that since Fourier’s law describes diffusion (under limiting assumptions) and it has shown to be ineffective in describing heat transfer for very thin films, that diffusion cannot describe heat transfer in thin films and one should look to a radiative description instead. If one considers diffusion in the sense of random motion, as invisaged by the original builders of the subject (Smoluchowski, Einstein, Ornstein et al.), instead of a temperature gradient, the idea that diffusion can govern thermal transport at this scale is not surprising. Indeed, the NHE is essentially a diffusion equation that describes the motion of particles up to the point of true randomness (isotropy) as well as thereafter.

scholarly journals Thermal Characterization and Modelling of AlGaN-GaN Multilayer Structures for HEMT Applications

Energies ◽  
2020 ◽  
Vol 13 (9) ◽  
pp. 2363 ◽  
Author(s):  
Lisa Mitterhuber ◽  
René Hammer ◽  
Thomas Dengg ◽  
Jürgen Spitaler
Keyword(s):  
Thermal Conductivity ◽  
Thermal Transport ◽  
Phonon Transport ◽  
Thermal Design ◽  
High Electron ◽  
Transport Mechanisms ◽  
Von Karman ◽  
Hemt Structure ◽  
Von Kármán ◽  
Thermal Conductivities

To optimize the thermal design of AlGaN-GaN high-electron-mobility transistors (HEMTs), which incorporate high power densities, an accurate prediction of the underlying thermal transport mechanisms is crucial. Here, a HEMT-structure (Al0.17Ga0.83N, GaN, Al0.32Ga0.68N and AlN on a Si substrate) was investigated using a time-domain thermoreflectance (TDTR) setup. The different scattering contributions were investigated in the framework of phonon transport models (Callaway, Holland and Born-von-Karman). The thermal conductivities of all layers were found to decrease with a temperature between 300 K and 773 K, due to Umklapp scattering. The measurement showed that the AlN and GaN thermal conductivities were a magnitude higher than the thermal conductivity of Al0.32Ga0.68N and Al0.17Ga0.83N due to defect scattering. The layer thicknesses of the HEMT structure are in the length scale of the phonon mean free path, causing a reduction of their intrinsic thermal conductivity. The size-effect of the cross-plane thermal conductivity was investigated, which showed that the phonon transport model is a critical factor. At 300 K, we obtained a thermal conductivity of (130 ± 38) Wm−1K−1 for the (167 ± 7) nm thick AlN, (220 ± 38) Wm−1K−1 for the (1065 ± 7) nm thick GaN, (11.2 ± 0.7) Wm−1K−1 for the (423 ± 5) nm thick Al0.32Ga0.68N, and (9.7 ± 0.6) Wm−1K−1 for the (65 ± 5) nm thick Al0.17Ga0.83N. Respectively, these conductivity values were found to be 24%, 90%, 28% and 16% of the bulk values, using the Born-von-Karman model together with the Hua–Minnich suppression function approach. The thermal interface conductance as extracted from the TDTR measurements was compared to results given by the diffuse mismatch model and the phonon radiation limit, suggesting contributions from inelastic phonon-scattering processes at the interface. The knowledge of the individual thermal transport mechanisms is essential for understanding the thermal characteristics of the HEMT, and it is useful for improving the thermal management of HEMTs and their reliability.

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