Accession Number : AD0678440

Title :   THERMAL CONDUCTIVITY OF SILICON IN THE BOUNDARY SCATTERING REGIME.

Descriptive Note : Technical rept.,

Corporate Author : PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF PHYSICS

Personal Author(s) : Hurst,Wilbur Scott

Report Date : OCT 1968

Pagination or Media Count : 175

Abstract : Thermal conductivity measurements on high-resistivity single crystals of silicon were made in the phonon boundary-scattering regime. The conductivities of samples with rough surfaces had a nearly T to the 3rd power dependence, in close agreement with the theory of Casimir. The conductivity did not change with different crystallographic rod faces for a given rod axis. However, the conductivity showed a strong dependence upon the crystallographic orientation of the rod axis of the sample, the conductivity of a sample having a (100) rod axis being nearly double that of an equal-sized sample with a (111) rod axis. In silicon, the phonon velocities are anisotropic, but it does not appear that the inclusion of the anisotropy in the Casimir formulation would be sufficient to explain this effect. For both rod axes, the change in conductivity with crystal dimensions is in agreement with the modified size-effect theory of Berman, Simon, and Ziman. For rough samples of rectangular cross-section, the effective diameter is the harmonic mean width rather than the geometric mean usually assumed. However, the conductivity deviates strongly from the T to the 3rd power law below 1.7K. Highly polished surfaces gave a large increase in conductivity, indicating largely specular reflection of the phonons. The temperature dependence was much less than cubic, indicating that the amount of specularity is wavelength dependent. Very smooth surfaces had a diffuseness f = 0.10 at 1.5K in the theory of Berman, Simon and Ziman, and confirmed the predicted large dependence of conductivity upon the ratio of crystal radius to length. (Author)

Descriptors :   (*SILICON, THERMAL CONDUCTIVITY), (*CRYOGENICS, SILICON), SINGLE CRYSTALS, PHONONS, SCATTERING, MEASUREMENT, SURFACE ROUGHNESS

Subject Categories : Solid State Physics
      Thermodynamics

Distribution Statement : APPROVED FOR PUBLIC RELEASE