Combined EPR and Photoluminescence Study of Electron and Proton Irradiated 3C-SiC

In past few years, point defects in silicon carbide (SiC) have been identified as promising for applications in quantum technologies [1]. A variety of point defects in hexagonal SiC [2], including VSi and VSiVC have been optically isolated and used as single defect-based spin qubits with long coherence time [3-5]. All of this, proves that these point defects allow the SiC to be a very favorable candidate for quantum applications especially, solid state quantum bits (Qubits) and single photon source (SPS). Most of these studies were carried out on the hexagonal polytypes 4H-SiC and 6H-SiC, although the 3C-SiC polytype presents the unique advantage of integration possibility on standard Si wafer. This is due to the amount of defects (dislocation mainly) in the 3C-SiC heteroepitaxy on Si which are detrimental for long coherence time considering Qubit application. Consequently, the goal of the present study is the investigation of point defects formation after implantation by proton H + (300 keV) and irradiation by electron e-(0.8 and 2 MeV) in 3C-SiC (respectively 3C-SiC and 3C-SiC ) for SPS application purpose. Toward this end, we have combined two characterization techniques, the photoluminescence (PL) and the electron paramagnetic resonance (EPR). PL (12K) and EPR (70-300K) measurements will be presented in order to analyze precisely the signatures of point defects generated after these two types of irradiations. The effects of the thermal annealing (500-1000°C) were also investigated. PL spectra both for 3C-SiC and 3C-SiC are presented in figure 1 for the annealing temperatures giving the highest PL signal (1000°C for 3C-SiC and 750°C for 3C-SiC ). We notice first that the whole PL signal is higher for 3C-SiC . In this case the spectrum is dominated by the DI defect line (possibly related to antisite pair [6]) and the E line (attributed to Si vacancy [7, 8]) while in electron irradiated sample the  line (attributed to CSiVC in a 3C-SiC nanocrystal [8]) dominates as previously reported [9]. A strong zero phonon line at 1.6 eV also appears for 3C-SiC with its phonon replica. This line was previously observed also for neutron and proton irradiated 3C-SiC and at present is of unknown origin [10, 11]. In the infrared range, the proton implantation is also more efficient to produce the VcVsi PL line with an optimum luminescence for 750°C annealing. All together, these results show that, even if the energy transferred to the host atoms during electron irradiation is quite above the displacement thresholds for both C and Si, defects involving Si vacancy are more pronounced in 3C-SiC samples. EPR spectra for 3C-SiC for isochronal annealing (30 min.) at different temperatures are presented in figure 2. The spin-three-half negatively-charged Si vacancy (the T1 center) is a dominant defect in 3C-SiC epitaxial layers corresponding to the E line in the PL spectra. Similar to neutron irradiated 3C-SiC crystals the as-implanted not annealed 3C-SiC samples demonstrate an isotropic spectrum with the g-value of 2.0029 and a superhyperfine doublet with a splitting typical to the T1 center