Thermal conductivity of hydrogenated amorphous silicon (original) (raw)
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High Thermal Conductivity of a Hydrogenated Amorphous Silicon Film
Physical Review Letters, 2009
We measured the thermal conductivity of an 80 m thick hydrogenated amorphous silicon film prepared by hot-wire chemical-vapor deposition with the 3! (80-300 K) and the time-domain thermoreflectance (300 K) methods. The is higher than any of the previous temperature dependent measurements and shows a strong phonon mean free path dependence. We also applied a Kubo based theory using a tight-binding method on three 1000 atom continuous random network models. The theory gives higher for more ordered models, but not high enough to explain our results, even after extrapolating to lower frequencies with a Boltzmann approach. Our results show that this material is more ordered than any amorphous silicon previously studied.
Thermal conductivity measurements of thin amorphous silicon films by scanning thermal microscopy
Thermal conductivity measurements of thin amorphous silicon films performed with a micro-thermistance mounted on an atomic force microscope are presented. A specific thermal model is implemented, and an identification procedure is proposed to extract the film contribution from the apparent thermal conductivity. Results show agreement with the literature regarding interface resistance data, but lower thermal conductivity values are obtained.
Thermal conductivity accumulation in amorphous silica and amorphous silicon
We predict the properties of the propagating and nonpropagating vibrational modes in amorphous silica (a-SiO 2 ) and amorphous silicon (a-Si) and, from them, thermal conductivity accumulation functions. The calculations are performed using molecular dynamics simulations, lattice dynamics calculations, and theoretical models. For a-SiO 2 , the propagating modes contribute negligibly to thermal conductivity (6%), in agreement with the thermal conductivity accumulation measured by Regner et al. [Nat. Commun. 4, 1640]. For a-Si, propagating modes with mean-free paths up to 1 μm contribute 40% of the total thermal conductivity. The predicted contribution to thermal conductivity from nonpropagating modes and the total thermal conductivity for a-Si are in agreement with the measurements of Regner et al. The accumulation in the measurements, however, takes place over a narrower band of mean-free paths (100 nm-1 μm) than that predicted (10 nm-1 μm).
Thermopower and Conductivity Activation Energies in Hydrogenated Amorphous Silicon
MRS Proceedings, 1996
The long range fluctuation model has been widely used to account for the difference in activation energies seen experimentally in dark conductivity and thermopower measurements in hydrogenated amorphous silicon. We report on a test of this model using measurements of the conductivity and thermoelectric effects carried out in both open and short circuit configurations. While the thermopower activation energy is less than that of the dark conductivity, the short circuit Seebeck conductivity is found to be nearly identical to the dark conductivity in both activation energy and magnitude, consistent with the long range fluctuation model.
Physical Review B, 2007
We present an ab initio calculation of the DC conductivity of amorphous silicon and hydrogenated amorphous silicon. The Kubo-Greenwood formula is used to obtain the DC conductivity, by thermal averaging over extended dynamical simulation. Its application to disordered solids is discussed. The conductivity is computed for a wide range of temperatures and doping is explored in a naive way by shifting the Fermi level. We observed the Meyer-Neldel rule for the electrical conductivity with EMNR=0.06 eV and a temperature coefficient of resistance close to experiment for a-Si:H. In general, experimental trends are reproduced by these calculations, and this suggests the possible utility of the approach for modeling carrier transport in other disordered systems.
Measurements of the thermal conductivity of amorphous materials with low dielectric constants
Physica B-condensed Matter, 2002
We report on measurements of the thermal conductivity of a number of amorphous materials, including several that have a low dielectric constant and which are of current interest for use as insulators in computer chips. The samples are thin films deposited onto Si substrates. Measurements are made using an optical technique in which the film is heated with a picosecond
Thermal conductivity measurement of amorphous Si/SiGe multilayer films by 3 omega method
International Journal of Thermal Sciences, 2013
The cross-plane thermal conductivities of five amorphous Si/Si 0.75 Ge 0.25 multilayer films deposited by magnetron sputtering with period thicknesses ranging from 2.5 nm to 50 nm were investigated by a differential 3u method at room temperature. The measurement results demonstrate that the thermal conductivities of amorphous Si/Si 0.75 Ge 0.25 multilayer films are independent of period thickness and are comparable to the corresponding result calculated according to the Fourier heat conduction theory using constituent materials' thermal conductivities. Structure disorder and sharp interfaces of multilayer films were confirmed by X-ray diffraction and scanning electron microscopy. The results indicate that in amorphous Si/Si 0.75 Ge 0.25 multilayer system interface effects do not play a key factor to thermal transport at room temperature due to significant reduction of phonon mean free path induced by the structure disorder.
Effects of microstructure on transport properties of undoped hydrogenated amorphous silicon films
Applied Physics Letters, 1993
Electronic transport properties have been investigated in undoped hydrogenated amorphous silicon (a-Si:H) materials whose microstructure and void fraction are changed by deposition temperature ( r,) . The hydrogen content in these materials decreases from 15 to 5 at. % and the void fraction by 14% as T, is raised from 200 to 350 "C. The photo and dark conductivities are measured from 40 to 190 "C and extended state electron mobilities are derived from a self-consistent analysis. The room temperature mobilities are found to increase from 0.8 to 30 cm2/V s and become less temperature dependent as T, increases. These temperature activated mobilities explain the Meyer-Neldel rule [Z. Tech. Phys. 18, 588 (1937)] in a-Si:H materials whose dark conductivity activation energies are greater than 0.4 eV where it cannot be explained by the statistical shift of the Fermi level.
Properties of hydrogenated amorphous silicon produced at high temperature
Hydrogenated amorphous silicon thin ®lm transistors (a-Si:H TFTs) were fabricated by plasma enhanced chemical vapor deposition system. Silicon nitride and a-Si:H were deposited at 150°C. The a-Si:H TFT had ®eld eect mobility of 0.75 cm 2 /V s, sub-threshold voltage swing of 0.5 V/dec and on/o current ratio >1.5´10 6 . The hydrogen was added during the gate insulator of SiN x deposition. The deposition rate of SiN x decreased and the SiH/NH ratio increased with the increasing H 2 gas¯ow rate. The a-Si:H TFT fabricated with the gate insulator with larger SiH/NH ratio had smaller threshold voltage and less threshold voltage shift after the gate bias stress (30 V, 10 3 s). Ó
Physical Review Materials, 2021
Hydrogenated amorphous dielectric thin films are critical materials in a wide array of technologies. In this work, we present a thorough investigation of the thermal conductivity of hydrogenated amorphous silicon nitride (atextensuremath−mathrmSiNx:mathrmH)(a\text{\ensuremath{-}}{\mathrm{SiN}}_{x}:\mathrm{H})(atextensuremath−mathrmSiNx:mathrmH), a ubiquitously used material in which the stoichiometry plays a direct role in its functionality and application. In particular, through chemical, vibrational, and structural analysis in tandem with thermal conductivity measurements on chemically variant silicon nitride films, we show that hydrogen incorporation into silicon nitride disrupts the bonding among silicon and nitrogen atoms, and directly impacts the thermal conductivity, leading to as much as a factor of 2.5 variation in heat transfer. This variability, driven by the change in hydrogen content, is fundamentally related to the changes in the average atomic distances, as we experimentally measure with selected-area electron diffraction and computatio...