Ultrahigh thermal conductivity of isotopically enriched silicon

Abstract

Most of stable elements (about eighty) have two and more stable (non-radioactive) isotopes. The physical properties of materials composed of such elements depend on the isotopic abundance in some extent. Remarkably strong isotope effect is observed in the phonon thermal conductivity, the principal mechanism of heat conduction in nonmetallic crystals. An isotopic disorder due to random distribution of the isotopes in the crystal lattice sites results in a rather strong phonon scattering and, consequently, in a reduction of thermal conductivity. In this paper we present new results of accurate and precise measurements of thermal conductivity κ(T) for silicon single crystals having three different isotopic compositions at temperatures T from 2.4 to 420 K. The highly enriched crystal containing 99.995% of 28 Si, which is one of the most perfect crystal ever synthesized, demonstrates the thermal conductivity about 450 W cm −1 K −1 at 24 K, the highest measured value among bulk dielectrics, which is ten times greater than one for its counterpart nat Si with the natural isotopic constitution. For highly enriched crystal 28 Si and crystal nat Si the measurements were performed for two orientations [001] and [011], a magnitude of the phonon focusing effect on thermal conductivity was determined accurately at low temperatures. The κ(T) measured in this work gives the most accurate approximation of the intrinsic thermal conductivity of single crystal silicon which is determined solely by the anharmonic phonon processes and diffusive boundary scattering over a wide temperature range.

Ab initio study of lattice dynamics of group IV semiconductors using pseudohybrid functionals for extended Hubbard interactions

“…Our LDA and PBEsol calculations are almost identical, and produce similar or slightly smaller values for C at low temperature but underestimated for Si and Ge compared to experiment [99][100][101][102][103]. This result is due to our choice of the experimental lattice constants for phonon calculations to analyze the functional dependence at the same footing.…”

“…The PBEsol and LDA give almost identical results. Experimental values of lattice thermal conductivity (C[99,100], Si[101], and Ge[102,103]) are plotted in open circles.…”

Thermal conductivity of strained silicon: Molecular dynamics insight and kinetic theory approach

“…2. Firstly, it should be noted that thermal conductivity evaluated with MD simulations overestimates the experimental results for natural 61 and highly isotopically enriched 62 Si (κ=130-160 W/(m•K) for 300 K). As discussed previously, MD is based on classical laws of motion and quantum phenomena are not taken into account.…”

Isotopic enrichment of silicon by high fluence $^{28}$Si$^-$ ion implantation

“…Long coherence times for donor spin qubits in a 28 Si epilayer with 800 ppm residual 29 Si [9] have been demon- strated, with Hahn-echo decay times of around 1 ms for electrons and 1.75 s for ionised donor nuclei measured for a single P donor at low temperature, which can be further extended with dynamical decoupling [10]. Isotope engineering of semiconductor materials also has applications for increased thermal conductivity [11][12][13], capable of improved heat dissipation in Si integrated circuits [14].…”