Dielectric loss and energy distribution of the shallow levels in CVD diamonds

The experimental data and calculations of the dielectric loss in polycrystalline CVD diamonds in the millimeter wave range and in wide temperature range of 1–300 K are analyzed. The theoretical temperature dependencies of the loss were calculated in assumption that the loss is due to the electrical conductance induced by thermal excitation of shallow levels. The continuous uniform activation energy distribution of shallow levels was assumed with additional narrow band at energies ∼ 0.001 eV and graphite-like inclusions were taken into account. A good coincidence was found for the theoretical temperature dependence with the experimental data on loss. These results correlate with the Q-DLTS continuous spectra corresponding to shallow levels obtained in the same samples. The results show the presence of acceptor shallow levels with a continuous energy spectrum and quasi-uniform activation energy distribution from ∼ 0.1 up to ∼ 0.003 eV. It is concluded that the millimeter wave losses in the CVD diamonds at the temperatures ∼ 30–300 K are mainly due to the thermal excitation of charge carriers from native shallow levels.An essential reduction (in the order of magnitude) of the dielectric loss at the edge of the CVD diamond disk after laser cutting (compared to the value in the center) was observed.