Thermal and optical properties of high purity CVD-diamond discs doped with boron and nitrogen

Abstract

The effect of nitrogen and boron doping on the thermal and optical properties of high purity CVD-diamond grown by microwave plasma (MW-CVD) and DC arc-jet chemical vapor deposition (DCAJ-CVD) is investigated. Boron and nitrogen doping was carried out by adding to the process gas trimethylborate and nitrogen, respectively. Secondary ion mass spectrometry (SIMS) was used to quantify the incorporated boron concentration. To decide whether or not nitrogen is substitutionally incorporated electron paramagnetic resonance (EPR) measurements were applied. The influence of the impurities on the thermal properties was investigated by measuring the temperature dependence of the thermal conductivity between 77 and approximately 450 K. Using the Klemens–Callaway-Theory, information about phonon scattering at point and extended defects was obtained. In the case of nitrogen addition to the MW-CVD process, no enhanced point defect scattering but instead an increase of scattering at extended defects or grain boundaries was observed. The nitrogen doped DCAJ-CVD sample showed the typical yellow color and EPR signal of diamond containing substitutional nitrogen. The point defect concentration determined by the Klemens–Callaway-Theory was six times higher as compared to the MW-CVD samples. CVD-diamond samples doped with 2.5×10 19 cm −3 boron showed a bright blue color and absorption features indicating substitutionally incorporated boron. An enhanced phonon scattering due to point defects was not observed.