Phonons with long mean free paths in a-Si and a-Ge

Abstract

We investigated phonons with long mean free paths (MFPs) in amorphous Si (a-Si) and amorphous Ge (a-Ge). The thermal conductivity of a-Si and a-Ge thin films prepared by magnetron sputtering was found to depend on film thickness and deposition temperature. From the film thickness dependence, we conclude that phonons with MFPs longer than 100 nm contribute to heat transport in a-Si and a-Ge. Also, as deposition temperature was increased, phonons with MFPs ranging from 100 to 250 nm in a-Si and from 15 to 250 nm in a-Ge increased.

Anomalous reduction of thermal conductivity in coherent nanocrystal architecture for silicon thermoelectric material

“…The recent paper reported that the κ value depended on the formation temperature and thickness [29]. The κ value of amorphous Si formed under similar formation temperature and thickness of our CSN film is 0.98-0.99 W m À 1 K À 1 [29]. The consistency of the κ values reported from several groups [26][27][28][29] exhibited the high reliability of its value.…”

“…The κ value of amorphous Si formed under similar formation temperature and thickness of our CSN film is 0.98-0.99 W m À 1 K À 1 [29]. The consistency of the κ values reported from several groups [26][27][28][29] exhibited the high reliability of its value. In order to investigate whether this anomalous reduction comes from unique properties of CSNs or from conventional interfacial thermal resistance and classical size (ballistic) effect [30] of Si thermal conductivity, we calculated κ for a superlattice (SL) of amorphous SiO 2 ($0.3 nm)/Si (thickness of t Si ) under two different scenarios: fully diffusive (open triangles) and quasi-ballistic Boltzmann phonon transport (close triangles), by using the finite element and Monte Carlo methods [31], respectively as shown in Figure 3b.…”

“…The κ value of amorphous Si has some variation. The recent paper reported that the κ value depended on the formation temperature and thickness [29]. The κ value of amorphous Si formed under similar formation temperature and thickness of our CSN film is 0.98-0.99 W m À 1 K À 1 [29].…”

Ultimate Confinement of Phonon Propagation in Silicon Nanocrystalline Structure

“…Although thermal energy in the amorphous materials is mainly transported by non-propagating diffusons 37 , it is known that there are also low frequency propagons 32 with mean free path exceeding tens of nanometers [38][39][40][41][42] . Such low frequency propagation is absent in SiNC because mean free paths of acoustic phonons are ultimately reduced as described above.…”

Modification of thermal conductivity and thermal boundary resistance of amorphous Si thin films by Al doping

“…This result is similar to the results for a-Si and a-Ge from previous reports. [23][24][25][26][27][28][29] Previous work shows that the thermal conductivity of a-Si lms with thicknesses less than 100 nm do not show observable lm size dependence. 24 If we assume this remains true for our Al-doped a-Si lms, by tting the two data points (50 and 100 nm, 50 and 150 nm) for each Al doping concentration, we can calculate the thermal conductivities of the 100 and 150 nm-thick lms.…”