Electrical Impedance Spectra Of Heavily Nitrogen-Doped Synthetic Diamond Single Crystals In Temperature Range Of 10-400 K

The electrical impedance spectra of synthetic diamond single crystals inhomogeniously doped with nitrogen at a concentration of 300 - 600 ppm, primarily in a form of A- and C-centers are studied at temperatures of 10 - 400 K in the frequency range of 10(4)-10(7) Hz. The characteristic properties of disordered electronic systems are revealed, as well as the contributions of bulk and contact layers with the Schottky barrier to the total signal. In the studied temperature range, the electrical resistance increases one order of magnitude as the temperature decreases, and it is inversely proportional to the frequency of an alternating current in the range of 10(4)-10(6) Hz with the exponent varying in the range of (-0.8) - (-1.2), characteristic of the transition from multihops to a single hop conductivity. The dielectric constant of the investigated nitrogen-doped diamond single crystals is weakly dependent on the frequency in this range, and decreases by about 10% when the temperature decreases, which is also typical for amorphous and disordered wide-bandgap semiconductors. For the first time, anomalies were detected in the form of an absolute local minimum of resistance shifting in the temperature range of 210-270 K upon the signal frequency, as well as a one order of a magnitude (at a frequency of 400 kHz), decrease in resistance at temperatures below 50 K. These anomalies may be related to the change in the energy spectrum of charge carriers, as well as in the magnetic ordering of paramagnetic nitrogen impurity centers and local superconductivity at low temperatures. Information about the energy spectrum of charge carriers and charge transfer in the high-frequency range is necessary for creating various quantum optoelectronic devices based on nitrogen-doped synthetic diamond single crystals, such as sensors and single-photon radiation sources based on dense arrays of single NV-centers.