Influence of nitrogen doping and annealing on the silicon vacancy in 4H−SiC

The silicon vacancy (VSi) in $4H$-SiC at its cubic site (V2-center) has shown significant promise for quantum technologies, due to coherent spin states, the mature material system, and stable optical emission. In these SiC-based applications, doping plays a crucial role. It can be used to control the charge state of VSi and formation of different types of defects. Despite its importance, there has been little research on the effects of doping. In this work, we perform a study of the effects of nitrogen doping and annealing on the photoluminescence (PL), optically-detected magnetic resonance (ODMR) contrast, and dephasing times of ensembles of V2 in epilayers of $4H$-SiC. The results show an enhancement of PL that depends on the electron irradiation dose for a given electron concentration, supported by theoretical modeling of the charge state of VSi in the presence of nitrogen. Nitrogen substituted for carbon is shown to very efficiently donate one electron to VSi. We also observe that the ODMR contrast can be increased from 0.5% in low doped SiC to 1.5% by nitrogen doping of 10¹⁷ to 10¹⁸0.16em0excm^-3 and annealing at 500-6000.16em0ex^∘C for one hour, with only a 20% decrease in PL compared to unannealed. Some of the improvement in contrast is offset by a reduction in T₂* at these doping levels, but the estimated cw ODMR shot-noise limited sensitivity is still 1.6 times higher than that of undoped, unannealed SiC.