Sources of thermal resistance in chemically vapor deposited diamond

Measurement of the strong gradient (with respect to the distance z from the substrate surface) in the local thermal conductivity of CVD diamond over a wide temperature range (4-400 K) provides a powerful tool for identifying the microscopic sources of thermal resistance. IR absorption and elastic recoil measurements in the same samples reveal the primary impurity to be hydrogen. However, quantitative comparison with the measured point-defect thermal resistivity, as well as with nuclear magnetic resonance studies, indicates that hydrogen is not by itself a strong source of thermal resistance. Rather, it is usually associated with defects or other impurities which do cause thermal resistance and as such the hydrogen is only a secondary indicator of thermal resistance. Mass-density measurements reveal a lower mass density near the substrate surface than near the growth surface. Quantitative arguments are given for the preferential location of point defects at grain boundaries and for the preferential alignment of dislocations and twin intersections with the growth direction, thus accounting for the large anisotropy observed in the conductivity in the range z approximate to 30 to 100 mu m.