Thermal conductivity of pink CVD diamond: Influence of nitrogen-related centers

Thermal conductivity κ(T) of single-crystal CVD diamond lightly doped (about 3 ppm) with nitrogen has been measured at temperatures from 5.7 to 410 K. The sample was carefully characterized by optical absorption and photoluminescence spectroscopy for the presence of impurities. Nine different optically active defects related with nitrogen, hydrogen, and silicon impurities have been identified and quantified. This pink-tint crystal showed a high thermal conductivity of 24.0±0.5 W cm−1 K−1 at room temperature, which is very close to the highest value ever measured at about 25 W cm−1 K−1 for diamonds of natural isotopic composition. At the same time, the κ(T) of the crystal showed strong suppression >10% at temperatures 6<T<120 K with a maximum decrease of 2.7 times at ≈40 K compared to high purity diamonds. This behavior of the conductivity is attributed to a phonon scattering by charge carriers bound to nitrogen-related impurity centers, which is ineffective, however, at room and higher temperatures. The κ(T) has been calculated within the model based on the Callaway theory taking into account the elastic phonon scattering off charge carriers (holes and electrons) in the ground states of doping centers, and a very good agreement between the measured and theoretical data has been achieved. The model also gives a good approximation to the experimental data for κ(T) given in the literature for synthetic and natural single-crystal diamonds.