Thermal conductance of metal–diamond interfaces at high pressure

Heat transfer across metal-semiconductor interfaces involves multiple fundamental transport mechanisms such as elastic and inelastic phonon scattering, and electron-phonon coupling within the metal and across the interface. The relative contributions of these different transport mechanisms to interface conductance remains unclear in the current literature. In this work, we use a combination of first-principles calculations under the density functional theory framework and heat transport simulations using the atomistic Green's function (AGF) method to quantitatively predict the contribution of the different scattering mechanisms to the thermal interface conductance of epitaxial CoSi 2 -Si interfaces. An important development in the present work is the direct computation of interfacial bonding from density functional perturbation theory (DFPT) and hence the avoidance of commonly used 'mixing rules' to obtain the cross-interface force constants from bulk material force constants. Another important algorithmic development is the integration of the recursive Green's function (RGF) method with Büttiker probe scattering that enables computationally efficient simulations of inelastic phonon scattering and its contribution to the thermal interface conductance. First-principles calculations of electron-phonon coupling reveal that crossinterface energy transfer between metal electrons and atomic vibrations in the semiconductor is mediated by delocalized acoustic phonon modes that extend on both sides of the interface, and phonon modes that are localized inside the semiconductor region of the interface exhibit negligible coupling with electrons in the metal. We also provide a direct comparison between simulation predictions and experimental measurements of thermal interface conductance of epitaxial CoSi 2 -Si interfaces using the time-domain thermoreflectance technique. Importantly, the experimental results, performed across a wide temperature range, only agree well with predictions that include all transport processes: elastic and inelastic phonon scattering, electron-phonon coupling in the metal, and electron-phonon coupling across the interface.2

Section: Introductionmentioning

confidence: 99%

Thermal transport across metal silicide-silicon interfaces: First-principles calculations and Green's function transport simulations

Sridhar

Feser

et al. 2017

“…Presently, G across metal-dielectric interfaces have been extensively measured [4][5][6][7][8][9] and modeled [10][11][12][13][14], but a systematic study of metal alloy composition's influence on G has not been considered.…”

mentioning

confidence: 99%

Thermal interface conductance across metal alloy–dielectric interfaces

Freedman

Davis

et al. 2016

“…Sadasivam et al 55 performed first-principles calculations of electron-phonon coupling near a C49 TiSi 2 -Si interface and found that the coupling of electrons with joint or interfacial phonon modes can potentially produce a conductance similar to the phonon-phonon interfacial conductance (note: in the present paper, we obtained the C54 phase of TiSi 2 which is the lower resistivity phase and is more commonly used for semiconductor applications). Inelastic phonon scattering has been identified as an important transport mechanism for material combinations with a large acoustic mismatch such as Pb and diamond 56,57 . In the case of CoSi 2 of Si(111), we show in a forthcoming publication that the high temperature behavior of interface conductance can be matched quite well by invoking these mechanisms 54 .…”

Section: A Thermal Interface Conductance Of Epitaxial and Non-epitaxmentioning

confidence: 99%

Thermal transport across metal silicide-silicon interfaces: An experimental comparison between epitaxial and nonepitaxial interfaces

Feser

Sridhar

et al. 2017

Silicides are used extensively in nano-and microdevices due to their low electrical resistivity, low contact resistance to silicon, and their process compatibility. In this work, the thermal interface conductance of TiSi2, CoSi2, NiSi and PtSi are studied using time-domain thermoreflectance. Exploiting the fact that most silicides formed on Si(111) substrates grow epitaxially, while most silicides on Si(100) do not, we study the effect of epitaxy, and show that for a wide variety of interfaces there is no dependence of interface conductance on the detailed structure of the interface. In particular, there is no difference in the thermal interface conductance between epitaxial and non-epitaxial silicide/silicon interfaces, nor between epitaxial interfaces with different interface orientations. While these silicide-based interfaces yield the highest reported interface conductances of any known interface with silicon, none of the interfaces studied are found to operate close to the phonon radiation limit, indicating that phonon transmission coefficients are non-unity in all cases and yet remain insensitive to interfacial structure. In the case of CoSi2, a comparison is made with detailed computational models using (1) full-dispersion diffuse mismatch modeling (DMM) including the effect of near-interfacial strain, and (2) an atomistic Green' function (AGF) approach that integrates near-interface changes in the interatomic force constants obtained through density functional perturbation theory. Above 100K the AGF approach significantly underpredicts interface conductance suggesting that energy transport does not occur purely by coherent transmission of phonons, even for epitaxial interfaces. The full-dispersion DMM closely predicts the experimentally observed interface conductances for CoSi2, NiSi, and TiSi2 interfaces, while it remains an open question whether inelastic scattering, cross-interfacial electron-phonon coupling, or other mechanisms could also account for the high temperature behavior. The effect of degenerate semiconductor dopant concentration on metal-semiconductor thermal interface conductance was also investigated with the result that we have found no dependencies of the thermal interface conductances up to (n-type or p-type) ≈ 1 × 10 19 cm −3 , indicating that there is no significant direct electronic transport and no transport effects which depend on long-range metal-semiconductor band alignment.