SOURCES OF THERMAL-RESISTANCE IN CHEMICALLY VAPOR-DEPOSITED DIAMOND

Measurement of the strong gradient (with respect to the distance z fro m the substrate surface) in the local thermal conductivity of CVD diam ond over a wide temperature range (4-400 K) provides a powerful tool f or identifying the microscopic sources of thermal resistance. IR absor ption and elastic recoil measurements in the same samples reveal the p rimary 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 associate d with defects or other impurities which do cause thermal resistance a nd as such the hydrogen is only a secondary indicator of thermal resis tance. 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 bou ndaries and for the preferential alignment of dislocations and twin in tersections with the growth direction, thus accounting for the large a nisotropy observed in the conductivity in the range z approximate to 3 0 to 100 mu m.