Solodovnyk, A.; Laguta, O.; Prokhorov, A.; Segantini, M.; Naydenov, B.; Neugebauer, P.; Greulich-Weber, S.; Kalabukhova, E.; Savchenko, D.: Spin dynamics of exchange-coupled nitrogen donors in heavily doped n-type 15R SiC monocrystals: Multifrequency EPR and EDMR study. Physical Review B 107 (2023), p. 155202/1-13
10.1103/PhysRevB.107.155202
Abstract:
Semiconductor devices based on 15R silicon carbide (SiC) show improved properties compared to other polytypes. Here, we report the investigation of nitrogen-doped 15R SiC monocrystals with (ND–NA)∼5×1018cm−3 using multifrequency electron paramagnetic resonance (EPR) and electrically detected magnetic resonance (EDMR) spectroscopic methods in the microwave (MW) frequency range from 9.4 to 328.84 GHz and in the temperature range from 4.2 to 300 K. A single intensive S line with S=1/2, at g⊥=2.0026(2), and g∥=2.0043(2) dominates the EPR spectrum in 15R SiC at T<160 K and was attributed to the exchange-coupled nitrogen (N) donors substituting quasicubic “k1” site having the deeper energy level in 15R SiC lattice. From the analysis of the temperature behavior of the integral intensity, magnetic field position, intensity, shape, and width of the S line, it was concluded that at T<90 K, the exchange coupling occurs between localized donor electrons, while at T=90−150 K the interaction between exchange-coupled N donors and conduction electrons takes place. In the temperature interval from 20 to 160 K, the S-line EPR width was characterized by a two-phonon Orbach relaxation process with the activation energy of ∼6.5 meV corresponding to the valley-orbit splitting values for N donors in 15R SiC. The variable-range hopping regime obeying the T1/4 law was found to take place at T<20 K leading to the appearance of the S line in the EDMR spectrum at low temperatures. The appearance of the EDMR signal from exchange-coupled N donors is caused by the EPR-induced temperature-increase mechanism and the spin-flip hops process. The results obtained from MW conductivity measurements agree with EPR and EDMR data. The temperature variation of MW conductivity was described by several processes, including the electron-hopping process between N donor impurity atoms at T<50 K with activation energy ɛ3=1.5 meV, electron transitions between Hubbard bands at T=50–100 K; the transition of the electrons from the donor energy levels to conduction band with ionization energy ɛ1=32 meV at T=100–200 K and scattering of the conduction electrons by ionized donors occurred at the temperature higher than 200 K.