## 4 Conclusions  
We have critically reviewed the processes in high-temperature sublimation growth of graphene in Ar atmosphere using closed graphite crucible with emphasis on buffer layer formation and free charge carrier properties of MLG and QFS-MLG on 4H-SiC. We have explored the effect of introducing Ar at different temperatures, \(T_{\rm Ar}\). We have found that the buffer layer coverage decreases with increasing \(T_{\rm Ar}\) with well-developed buffer layer for \(T_{\rm Ar}\) = 800 \({}^{\circ}\)C, while for \(T_{\rm Ar}\) = 1300 \({}^{\circ}\)C the buffer layer is just beginning to form. The observed suppression of buffer layer formation at higher \(T_{\rm Ar}\) is accompanied by surface oxidation of the uncovered regions of the SiC substrates. A scenario in which oxidation occurs during the annealing process is proposed to explain the peculiar shift of the buffer layer formation to higher temperatures. The latter leads to reduced \(sp^{3}\) hybridization content and defect densities in the buffer layer when grown on \(n\)-type conductive substrates. Growth on SI substrates results in significantly improved structural properties of the buffer layers, which is attributed to a slower graphitization process closer to equilibrium due to the reduced thermal conductivity of the substrate. For SI substrate \(T_{\rm Ar}\) plays a minor role for the \(sp^{3}\) hybridization content and defect densities in the buffer layer. A comprehensive study of the free charge density and mobility parameters of MLG and QFS-MLG with \(T_{\rm Ar}\) = 640 \({}^{\circ}\)C, \(T_{\rm Ar}\) = 800 \({}^{\circ}\)C and \(T_{\rm Ar}\) = 1300 \({}^{\circ}\)C and four different environmental conditions: freshly annealed in vacuum, after purging with dry N\({}_{2}\) (RH 0%) for \(\sim\)20 h, after purging with moist air (RH 45%) for \(\sim\)18 h and after ambient exposure for several months, allows us to draw the following conclusions:  
(i) successful efficient annealing of donors on and near the SiC surface can be inferred for MLG grown at 2000 \({}^{\circ}\)C independent of \(T_{\rm Ar}\);  
(ii) approximately 45 h purging with moist air (RH 45%) is needed to flip the conductivity of MLG from \(n\)-type to \(p\)-type and long term exposure to ambient leads to a saturation of the free hole density at \(\sim\)2 \(\times\) 10\({}^{12}\) cm\({}^{-2}\);  
(iii) the highest mobility of MLG is determined for \(T_{\rm Ar}\) = 1300 \({}^{\circ}\)C in both intrinsically \(n\)-type and ambient \(p\)-type doped situations. It is suggested that this is a result of reduced interface phonon scattering due to improved interface between MLG and the buffer layer rather than between the buffer layer and the SiC substrate;  
(iv) a free hole density of \(\sim\)1.0 \(\times\) 10\({}^{13}\) cm\({}^{-2}\) is suggested to be the intrinsic value for our QFS-MLG resulting from polarization doping in good agreement with the previously reported value of 8.6 \(\times\) 10\({}^{12}\) cm\({}^{-2}\)[60];  
(v) \(T_{\rm Ar}\) is found to have a profound effect on the free hole parameters of QFS-MLG. A significantly lower free hole density of \(\sim\)2 \(\times\) 10\({}^{12}\) cm\({}^{-2}\) is found in intrinsic QFS-MLG with \(T_{\rm Ar}\) = 1300 \({}^{\circ}\)C, which is attributed to additional surface donor states associated with incomplete buffer formation. Our findings contribute to establishing a comprehensive picture of high-temperature sublimation growth and provide guidance for growth parameters optimization depending on the targeted application of QFS-MLG and MLG on SiC. The following are available online at [[https://www.mdpi.com/2076-3](https://www.mdpi.com/2076-3)]([https://www.mdpi.com/2076-3](https://www.mdpi.com/2076-3)) 417/11/4/1891/s1, Figure S1: Representative AFM images and step height distributions of buffer layers grown on SI 4H-SiC with \(T_{\rm Ar}\) = 800 \({}^{\circ}\)C and \(T_{\rm Ar}\) = 1300 \({}^{\circ}\)C.  
individual contributions of the authors are as follows: conceptualization, VS. and V.D. ; methodology, N.A. and P.K. ; software, V.S.