Electrically active defects, conductivity, and millimeter wave dielectric loss in CVD diamonds

The native and impurity-induced defects, conductivity, and dielectric loss at frequencies 145-182 GHz in undoped and boron-doped CVD diamond films were investigated. The as-grown undoped diamond films displayed the acceptor point defects with a continuous energy spectrum and the activation energy of conductivity Ea∼0.7 eV in the temperature range T=80-540K. The B-doped film showed two discrete boron-induced levels with activation energy EA∼0.37 and 0.25 eV, and the activation energy of conductivity Ea∼0.3 and∼0.13 eV at the high and low temperatures, respectively. The activation energies EAL determined from the temperature dependencies (275-900 K) of the dielectric loss in millimeter wave range are in good agreement with the values Ea and EA deduced from the electrical measurements. This indicates that the millimeter wave losses in CVD diamond are mainly due to excitation of electrically active native and impurity-induced defects. The electron irradiation (2 MeV) changes the parameters of boron-induced levels, reduces the concentration of the native defects with the continuous energy spectrum, and strongly, by four orders of magnitude, reduces electrical conductivity.