Fig. 4: Stability of the V⁴⁺ charge state.

a Energy diagram showing the charge transition levels for V centres, the main dopants nitrogen (N) and boron (B), and intrinsic defects, such as carbon vacancy (V_C) and divacancy, (V_SiV_C) involved in the V charge state dynamics in SiC. A transition between the positively-charged and neutral states, for example, is labelled as (+/0). V⁴⁺ corresponds to the neutral (0) and V³⁺ to the negative (-) charge state. In sample A (n-type), the N shallow donor can compensate the acceptor levels of shallow B and V_C, pinning the Fermi level (E_F) at the N shallow donor level and stabilising V³⁺. In sample B (semi-insulating), the E_F is located at the \(\left(0| -\right)\) acceptor level of the divacancy if the concentration of the N donor is larger than that of the B acceptor or, vice versa, at the \(\left(+| 0\right)\) donor level of V_C. In both cases, V⁴⁺ is stabilised at equilibrium. b Decay of the V⁴⁺ charge state at increasing powers of the resonant CW excitation. V⁴⁺ is prepared by a 300 ms repump pulse and the PL decay over time is recorded as a function of the resonant laser power (see pulse sequence inset). The ionisation induced by the resonant excitation follows an exponential decay of the count rate for both samples (see Supplementary Note 2), with a weaker decay in sample B, where the Fermi level stabilises V⁴⁺. c Lifetime of the V⁴⁺ charge state when no optical excitation is present. The system is prepared in the V⁴⁺ state by a repump pulse and the PL emission intensity is then recorded as a function of the delay (τ) between the repump and the probe. The PL peak intensity, corresponding to the occupation of the V⁴⁺ charge state, is plotted against the delay τ for both samples (see Supplementary Note 2). In sample A, the V⁴⁺ charge state decays rapidly with a timescale of 129 ± 6 ms, while it survives for several seconds in sample B. Errors bars in (a) and (b) correspond to the standard deviations extracted from the fits.