Anderson Localization of Thermal Phonons Leads to a Thermal Conductivity Maximum (original) (raw)
Related papers
1993
We study both analytically and numerically phonon transmission fluctuations and localization in partially ordered superlattices with correlations among neighboring layers. In order to generate a sequence of layers with a varying degree of order we employ a model proposed by Hendricks and Teller as well as partially ordered versions of deterministic aperiodic superlattices. By changing a parameter measuring the correlation among adjacent layers, the Hendricks-Teller superlattice exhibits a transition from periodic ordering, with alternating layers, to the phase separated opposite limit; including many intermediate arrangements and the completely random case. In the partially ordered versions of deterministic superlattices, there is short-range order (among any N consecutive layers) and long range disorder, as in the N-state Markov chains. The average and fluctuations in the transmission, the backscattering rate, and the localization length in these multilayered systems are calculated based on the superlattice structure factors we derive analytically. The standard deviation of the transmission versus the average transmission lies on a universal curve irrespective of the specific type of disorder of the SL. We illustrate these general results by applying them to several GaAs-AlAs superlattices for the proposed experimental observation of phonon universal transmission fluctuations.
Decomposition of coherent and incoherent phonon conduction in superlattices and random multilayers
Physical Review B, 2014
Nonequilibrium molecular dynamics (NEMD) simulations on conceptual binary Lennard-Jones systems show that the thermal conductivity (κ) of a superlattice (SL) can be significantly reduced by randomizing the thicknesses of its layers, by which a SL becomes a random multilayer (RML). Such reduction in κ is a clear signature of coherent phonon that can be localized in RMLs. We build a two-phonon model that divides the overall heat conduction into coherent and incoherent phonon contributions. In SL both coherent and incoherent phonons contribute to heat conduction, while in RML coherent phonons are localized so only incoherent phonons contribute. This model can fit the length dependence of the thermal conductances predicted in our NEMD simulations very well. The ballistic-limit thermal conductance and the intrinsic mean free path (MFP) of both coherent and incoherent phonons, and the localization length of coherent phonons, are obtained by fitting our model to the NEMD simulation results. The significant increase in κ of SL with total length is due to the long MFP of coherent phonons, and the lower κ of RML than SL is caused by the localization of coherent phonons.
High conductance in random superlattices with correlated disorder
1996
We study dc conductance of disordered GaAs-Ga1− xAlxAs superlattices where the disorder is intentional and short-range correlated. We consider Ga1− xAlxAs layers of the same thickness, where GaAs layers present two different thicknesses randomly distributed along the growth direction, with the constraint that one of them always appears in pairs. A set of almost unscattered electron states is observed in spite of the disorder, revealing itself through a distinct conductance maximum.
We demonstrate the existence of a coherent transport of thermal energy in superlattices by introducing a microscopic definition of the phonon coherence length. A criterion is provided to distinguish the coherent transport regime from diffuse interface scattering and discuss how these can be specifically controlled by several physical parameters. Our approach provides a convenient framework for the interpretation of previous thermal conductivity measurements and calculations; it also paves the way for the design of a new class of thermal interface materials.
2017 IEEE International Reliability Physics Symposium (IRPS), 2017
The ability to grow heterostructures with highquality interfaces brings great flexibility to the design and development of modern electronic and optoelectronic devices. While nearly perfect from an electronic standpoint, these interfaces are exceedingly disruptive to thermal transport and are a major contributor to anisotropic heat conduction and localized heating. Doping, alloying, and strain-all commonly employed when tailoring the electronic and optical properties of heterostructures-are also highly detrimental to the transport of phonons, the dominant carriers of heat in semiconductors. From the theoretical standpoint of phonon dynamics in disordered systems, we discuss the present understanding of nanoscale thermal transport and its profound sensitivity to any deviation from single-crystallinity. The roles that boundaries, interfaces, point defects, and strain play in thermal transport and localized heating are illustrated on several examples of semiconductor nanostructures, such as nanowires, thin films, superlattices, and quantum cascade lasers.
Observation of Carrier Localization in Intentionally Disordered Gaas/Gaalas Superlattices
Physical Review Letters, 1986
The carrier localization and the inhibition of carrier transport along the growth axis (vertical transport) are studied by means of photoluminescence experiments performed at 1.7 K in purposely disordered GaAs/GaAlAs superlattices. When the well widths are randomly varied, minibands of extended states shrink and localized states are created in their tails. Consequently the vertical transport efficiency decreases and sharply vanishes when disorder induces fluctuations of the eilenenergies which are comparable to half of the unperturbed superlattice bandwidth. By an increase of temperature the vertical transport becomes thermally activated.
Intrinsic to extrinsic phonon lifetime transition in a GaAs–AlAs superlattice
We have measured the lifetimes of two zone-center longitudinal acoustic phonon modes, at 320 and 640 GHz, in a 14 nm GaAs/2 nm AlAs superlattice structure. By comparing measurements at 296 and 79 K we separate the intrinsic contribution to phonon lifetime determined by phonon-phonon scattering from the extrinsic contribution due to defects and interface roughness. At 296 K, the 320 GHz phonon lifetime has approximately equal contributions from intrinsic and extrinsic scattering, whilst at 640 GHz it is dominated by extrinsic effects. These measurements are compared with intrinsic and extrinsic scattering rates in the superlattice obtained from first-principles lattice dynamics calculations. The calculated room-temperature intrinsic lifetime of longitudinal phonons at 320 GHz is in agreement with the experimentally measured value of 0.9 ns. The model correctly predicts the transition from predominantly intrinsic to predominantly extrinsic scattering; however the predicted transition occurs at higher frequencies. Our analysis indicates that the 'interfacial atomic disorder' model is not entirely adequate and that the observed frequency dependence of the extrinsic scattering rate is likely to be determined by a finite correlation length of interface roughness.
Coherent Phonon Heat Conduction in Superlattices
Science, 2012
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Metal-insulator transition in random Kronig-Penney superlattices with long-range correlated disorder
Physical Review B, 2006
We study the electronic properties of disordered GaAs-AlxGa1−xAs semiconductor superlattices with structural long-range correlations. The system consists of quantum barriers and wells with different thicknesses and heights which fluctuate around their mean values randomly, following a long-range correlated pattern of fractal type characterized by a power spectrum of the type S(k) ∝ 1/k (2α−1) , where the exponent α quantifies the strength of the long-range correlations. For a given system size, we find a critical value of the exponent α (αc) for which a metal-insulator transition appears: for α < αc all the states are localized, and for α > αc, we find a continuous band of extended states. We also show that the existence of extended states causes a strong enhancement of the DC conductance of the superlattice at finite temperature, which increases in many orders of magnitude when crossing from the localized to the extended regime. Finally, we perform finite size scaling and we obtain the value of the critical exponent αc in the thermodynamic limit, showing that the transition is not a finite-size effect.