Characterization of boron-doped single-crystal diamond by electrophysical methods (review)

A critical analysis of the existing methods of controlling the concentration of impurity and majority charge carriers in wide bandgap semiconductors and the issues of improvement of modern diagnostics of the main electrophysical properties of single–crystal diamond are considered based on the results of our studies and the works of other authors. It was found that independent assessment of impurity concentration and concentration of free charge carriers is of fundamental importance for semiconductor diamond due to very low (less than 1%) degree of ionization of the introduced impurity. The advantages and prospects of admittance spectroscopy as a diagnostic method for ultrawide bandgap semiconductors are shown and solutions aimed at the correct interpretation of the experimental data are proposed. The high ionization energy of boron impurity in diamond (370 meV) results in a strong frequency dispersion of the measured barrier capacitance. It is shown that under disturbance of quasi-static conditions in capacitance-voltage measurements, low frequencies and high temperatures should be used for correct assessment of the charge carrier concentration. The results of electrophysical studies are compared with traditional measurements of impurity concentration in diamond by optical methods. A decrease of hole activation energy from the boron impurity level from 325 to 100 meV was found upon increasing the boron concentration NA from 2$\cdot$10$^{16}$ to 4$\cdot$10$^{19}$ cm$^{-3}$. The transition to the hopping mechanism of conductivity within the impurity (acceptor) band with thermal activation energy of 10–20 meV was registered for NA $\ge$ 5$\cdot$10$^{18}$ cm$^{-3}$ at temperatures of 120–150 K.