Radiation-Induced Defects in Electron-Irradiated Pure and Nitrogen-Doped High-Pressure High-Temperature Diamond: Decrease in the Thermal Conductivity

Abstract

The effect of 3-MeV electron irradiation at a fluence of 5 × 10¹⁸ cm^–2 on the thermal conductivity κ(T) of type IIa and type Ib high-pressure high-temperature diamond single crystals with nitrogen concentrations of less than 1 ppm and approximately 70 ppm, respectively, has been studied. Irradiation reduces the thermal conductivity κ(T) over the entire studied temperature range 5 K < T < 410 K. For pure diamond, the strongest decrease in κ(T) by a factor of 350 is observed at 25–30 K, but the thermal conductivity κ(T) at room temperature T = 300 K decreases by a factor of only 1.56. Compared to pure diamond, the thermal conductivity of irradiated doped diamond decreases much less strongly at low temperatures, but more strongly at T > 140 K. After irradiation, the difference in the reduction of the thermal conductivity between the two types of diamond is so large that κ(T) for doped diamond is larger than that for pure diamond at T < 50 K and is an order of magnitude larger at 5 K. Experimental data allow the assumption that the rate of phonon scattering by neutral radiation defects—vacancies, their aggregates, and Frenkel pairs (pairs of interacting interstitial atoms and vacancies)—in pure diamond is much higher than that by such negatively charged defects in nitrogen-doped diamond at low temperatures. However, the ratio of scattering rates becomes inverse at high temperatures.