Local thermal conductivity in chemical-vapor-deposited diamond

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Abstract
The thermal conductivity has been measured in the temperature range 5–400 K for a series of chemical‐vapor‐deposited diamond samples differing only in thickness. By analyzing the conductance, a local conductivity is extracted as a function of height z above the substrate on which the samples were grown. An analysis of the temperature dependence of the conductivity at any given height yields the phonon scattering mechanisms as a function of z. Point defects and extended defects of approximately 1.5 nm diam appear to be the most important phonon scattering entities at room temperature, but their scattering strengths decrease with height above the substrate. At a height z≊300 μm, the material is sufficiently perfect that scattering from extended defects at room temperature is negligible and scattering from point defects is only slightly higher than that attributable to naturally occurring 13C. The observed anisotropy of the thermal conductivity is consistent with aggregation of point defects and extended defects at or near grain boundaries. The z dependence of the scattering from these defects suggests that the quality of the grain boundaries increases with z. For z≳300 μm, the conductivity is equal to that of single crystals of gem‐quality type IIa diamond.