skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Atomistic Simulation of the Size and Orientation Dependences of Thermal Conductivity in GaN Nanowires

Abstract

The thermal conductivity of GaN nanowires has been determined computationally, by applying nonequilibrium atomistic simulation methods using the Stillinger-Weber [Phys. Rev. B 31, 5262 (1985)] potentials. The simulation results show that the thermal conductivity of the GaN nanowires is smaller than that of a bulk crystal and increases with increasing diameter. Surface scattering of phonons and the high surface to volume ratios of the nanowires are primarily responsible for the reduced thermal conductivity and its size dependence behavior. The thermal conductivity is also found to decrease with increasing temperature, which is due to phonon-phonon interactions at high temperatures. The thermal conductivity also exhibits a dependence on axial orientation of the nanowires.

Authors:
; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Org.:
USDOE
OSTI Identifier:
908730
Report Number(s):
PNNL-SA-54253
Journal ID: ISSN 0003-6951; APPLAB; 8208; KC0201020; TRN: US0703753
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters, 90(16):Art. No. 161923; Journal Volume: 90; Journal Issue: 16
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; ORIENTATION; PHONONS; SCATTERING; SIMULATION; THERMAL CONDUCTIVITY; Thermal conductivity; Nanowires; GaN; Computer simulations; Environmental Molecular Sciences Laboratory

Citation Formats

Wang, Zhiguo, Zu, Xiaotao, Gao, Fei, Weber, William J., and Crocombette, J.-P. Atomistic Simulation of the Size and Orientation Dependences of Thermal Conductivity in GaN Nanowires. United States: N. p., 2007. Web. doi:10.1063/1.2730747.
Wang, Zhiguo, Zu, Xiaotao, Gao, Fei, Weber, William J., & Crocombette, J.-P. Atomistic Simulation of the Size and Orientation Dependences of Thermal Conductivity in GaN Nanowires. United States. doi:10.1063/1.2730747.
Wang, Zhiguo, Zu, Xiaotao, Gao, Fei, Weber, William J., and Crocombette, J.-P. Mon . "Atomistic Simulation of the Size and Orientation Dependences of Thermal Conductivity in GaN Nanowires". United States. doi:10.1063/1.2730747.
@article{osti_908730,
title = {Atomistic Simulation of the Size and Orientation Dependences of Thermal Conductivity in GaN Nanowires},
author = {Wang, Zhiguo and Zu, Xiaotao and Gao, Fei and Weber, William J. and Crocombette, J.-P.},
abstractNote = {The thermal conductivity of GaN nanowires has been determined computationally, by applying nonequilibrium atomistic simulation methods using the Stillinger-Weber [Phys. Rev. B 31, 5262 (1985)] potentials. The simulation results show that the thermal conductivity of the GaN nanowires is smaller than that of a bulk crystal and increases with increasing diameter. Surface scattering of phonons and the high surface to volume ratios of the nanowires are primarily responsible for the reduced thermal conductivity and its size dependence behavior. The thermal conductivity is also found to decrease with increasing temperature, which is due to phonon-phonon interactions at high temperatures. The thermal conductivity also exhibits a dependence on axial orientation of the nanowires.},
doi = {10.1063/1.2730747},
journal = {Applied Physics Letters, 90(16):Art. No. 161923},
number = 16,
volume = 90,
place = {United States},
year = {Mon Apr 16 00:00:00 EDT 2007},
month = {Mon Apr 16 00:00:00 EDT 2007}
}
  • Molecular dynamics simulations with Stillinger-Weber potentials were used to study the response of wurtzite-type single crystalline GaN nanowires to a tensile strain along the axial direction. Nanowires with axial orientations along the [0001], [1 00] and [11 0] crystallographic directions, which correspond to experimentally synthesized nanowires, were studied. The results reveal that the nanowires with different axial orientations show distinctly different deformation behavior under loading. The brittle to ductile transition (BDT) was observed in the nanowires oriented along the [0001] direction and the BDT temperatures lie in the temperature range between 1500 and 1800 K. The nanowires oriented along themore » [11 0] direction exhibit slip in the {01 0} planes; whereas the nanowires oriented along the [1 00] direction fracture in a cleavage manner under tensile loading. It should be emphasized that multiple yield stresses were observed during different stages in the [11 0]-oriented nanowires. In general, Young's modulus of the GaN nanowires decreases with decreasing diameter of the nanowires.« less
  • Graphical abstract: Temperature dependence of calculated lattice thermal conductivity of Wurtzite GaN nanowires. Highlights: Black-Right-Pointing-Pointer A modified Callaway model is used to calculate lattice thermal conductivity of Wurtzite GaN nanowires. Black-Right-Pointing-Pointer A direct method is used to calculate phonon group velocity for these nanowires. Black-Right-Pointing-Pointer 3-Gruneisen parameter, surface roughness, and dislocations are successfully investigated. Black-Right-Pointing-Pointer Dislocation densities are decreases with the decrease of wires diameter. -- Abstract: A detailed calculation of lattice thermal conductivity of freestanding Wurtzite GaN nanowires with diameter ranging from 97 to 160 nm in the temperature range 2-300 K, was performed using a modified Callaway model.more » Both longitudinal and transverse modes are taken into account explicitly in the model. A method is used to calculate the Debye and phonon group velocities for different nanowire diameters from their related melting points. Effect of Gruneisen parameter, surface roughness, and dislocations as structure dependent parameters are successfully used to correlate the calculated values of lattice thermal conductivity to that of the experimentally measured curves. It was observed that Gruneisen parameter will decrease with decreasing nanowire diameters. Scattering of phonons is assumed to be by nanowire boundaries, imperfections, dislocations, electrons, and other phonons via both normal and Umklapp processes. Phonon confinement and size effects as well as the role of dislocation in limiting thermal conductivity are investigated. At high temperatures and for dislocation densities greater than 10{sup 14} m{sup -2} the lattice thermal conductivity would be limited by dislocation density, but for dislocation densities less than 10{sup 14} m{sup -2}, lattice thermal conductivity would be independent of that.« less
  • Gallium nitride (GaN) is a high-temperature semiconductor material of considerable interest. It emits brilliant light and has been considered as a key material for the next generation of high frequency and high power transistors that are capable of operating at high temperatures. Due to its anisotropic and polar nature, GaN exhibits direction-dependent properties. Growth directions along [001], [1-10] and [110] directions have all been synthesized experimentally. In this work, molecular dynamics simulations are carried out to characterize the mechanical properties of GaN nanowires with different orientations at different temperatures. The simulation results reveal that the nanowires with different growth orientationsmore » exhibit distinct deformation behavior under tensile loading. The nanowires exhibit ductility at high deformation temperatures and brittleness at lower temperature. The brittle to ductile transition (BDT) was observed in the nanowires grown along the [001] direction. The nanowires grown along the [110] direction slip in the {010} planes, whereas the nanowires grown along the [1-10] direction fracture in a cleavage manner under tensile loading.« less
  • Classical molecular dynamics simulation was used to irradiate a GaN nanowire with rear-earth erbium (Er). Ten cumulative irradiations were done using an ion energy of 37.5 keV on a 10 × 10 nm²surface area which corresponds to a fluence of 1 × 10¹³ cm⁻². We studied the location and types of defects produced in the irradiation. Er implantation leads to a net positive (expansion) strain in the nanowire and especially at the top region a clear expansion has been observed in the lateral and axial directions. The lattice expansion is due to the hydrostatic strain imposed by a large numbermore » of radiation induced defects at the top of the NW. Due to the large surface-to-volume ratio, most of the defects were concentrated at the surface region, which suggests that the experimentally observed yellow luminescence (YL) in ion implanted GaN NWs arises from surface defects. We observed big clusters of point defects and vacancy clusters which are correlated with stable lattice strain and the YL band, respectively.« less
  • Highlights: {yields} The structural stability, orientation effect and melting characteristic of zinc oxide (ZnO) nanowires are simulated by using the molecular dynamics with many-body tightbinding potential. {yields} The nanowire with a hexagonal cross section is more stable than that with other cross section type, namely, a rectangular, triangular, rhombohedral, octagonal, and circular cross section. {yields} The structural stability and melting temperature of a nanowire is sensitive to its diameter because of the surface energy and unfavorable coordination. -- Abstract: The structural stability, orientation effect and melting characteristic of zinc oxide (ZnO) nanowires are simulated by using the molecular dynamics withmore » many-body tightbinding potential. The structural stability is affected by the geometric shape of the cross section of a nanowire. The nanowire with a hexagonal cross section is more stable than that with another cross section type, namely, a rectangular, triangular, rhombohedral, octagonal, and circular cross section. The structural stability and melting temperature of a nanowire is sensitive to its diameter because of the surface energy and unfavorable coordination. Remarkably, it is observed that hexagonal ZnO nanowires transform to metastable circular-type structures at temperatures lower than the melting point.« less