Electrically-detected electron paramagnetic resonance of point centers in 6H-SiC nanostructures

The results of investigation of electrically-detected electron paramagnetic resonance (EDEPR) and classical electron paramagnetic resonance (EPR) (X-band) for the identification of shallow and deep boron centers, N$V_{\mathrm{Si}}$ defects, and isolated silicon vacancies ($V_{\mathrm{Si}}$), which are formed directly during the preparation of planar nanostructures under conditions of silicon-vacancy injection at the SiO$_2$/$n$-6H-SiC interface without any subsequent irradiation, are presented. The prepared sandwich nanostructures are an ultra-narrow $p$-type quantum well, confined by $\delta$ barriers heavily doped with boron on an $n$-6H-SiC surface, which are self-ordered during pyrolytic-oxide deposition and subsequent short-time boron diffusion. The EDEPR data of point centers in sandwich nanostructures, prepared within the framework of Hall geometry, are recorded by measuring the field dependences of the magnetoresistance without an external cavity, microwave source and detector, due to the presence of microcavities embedded in the quantum-well plane and microwave generation under conditions of a stabilized source-drain current from $\delta$ barriers containing dipole boron centers. The obtained EDEPR spectra of the shallow and deep boron centers are analyzed using the data of EPR studies in 6H-SiC bulk crystals [10]. The EDEPR spectrum of the isolated silicon vacancy reveals both the negatively charged state $V_{\mathrm{Si}}^-$ ($S$ = 3/2) and the neutral state in hexagonal ($V_{\mathrm{Si}(h)}$) and quasicubic ($V_{\mathrm{Si}(k1,k2)}$) states ($S$ = 1). In turn, N$V_{\mathrm{Si}}$ defects are detected not only by the EDEPR method at 77 K, but also through the use of a Bruker ELEXSYS E580 EPP spectrometer at 9.7 GHz, in a temperature range of 5–40 K. The EDEPR and EPR spectra recorded on the same sandwich nanostructure are virtually identical and correspond to the center in the triplet state with spin $S$ = 1. The EPR spectrum, which is a lowintensity line doublet with a splitting value equal to $\Delta B$ = 237.6 mT, is observed in the background of the EPR spectrum from donors of nitrogen, the concentration of which in the $n$-6H-SiC initial sample was 5 $\cdot$ 10$^{18}$ cm$^{-3}$, whereas nitrogen donor centers are not revealed in the EDEPR spectrum because of total occupation by silicon vacancies inside the 6H-SiC sandwich nanostructure.