Abstract
In this work we have critically reviewed the processes in high-temperature sublimation growth of graphene in Ar atmosphere using closed graphite crucible. Special focus is put on buffer layer formation and free charge carrier properties of monolayer graphene and quasi-freestanding monolayer graphene on 4H–SiC. We show that by introducing Ar at higher temperatures, TAr, one can shift the formation of the buffer layer to higher temperatures for both n-type and semi-insulating substrates. A scenario explaining the observed suppressed formation of buffer layer at higher TAr is proposed and discussed. Increased TAr is also shown to reduce the sp3 hybridization content and defect densities in the buffer layer on n-type conductive substrates. Growth on semi-insulating substrates results in ordered buffer layer with significantly improved structural properties, for which TAr plays only a minor role. The free charge density and mobility parameters of monolayer graphene and quasi-freestanding monolayer graphene with different TAr and different environmental treatment conditions are determined by contactless terahertz optical Hall effect. An efficient annealing of donors on and near the SiC surface is suggested to take place for intrinsic monolayer graphene grown at 2000 ∘C, and which is found to be independent of TAr. Higher TAr leads to higher free charge carrier mobility parameters in both intrinsically n-type and ambient p-type doped monolayer graphene. TAr is also found to have a profound effect on the free hole parameters of quasi-freestanding monolayer graphene. These findings are discussed in view of interface and buffer layer properties in order to construct a comprehensive picture of high-temperature sublimation growth and provide guidance for growth parameters optimization depending on the targeted graphene application.
Highlights
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 monolayer graphene (MLG) and QFS-MLG on 4H–SiC
We have found that the buffer layer coverage decreases with increasing TAr with well-developed buffer layer for
The observed suppression of buffer layer formation at higher TAr is accompanied by surface oxidation of the uncovered regions of the SiC substrates
Summary
Introducing Ar at different temperatures during the graphitization process may provide an alternative pathway to influence the phase transition temperature between different surface reconstructions, and enable the growth of smooth MLG without the need of special pre-treatment. This approach has not been explored despite the intense investigation of buffer layer properties and optimization [4,31,32,33,34]. Sci. 2021, 11, 1891 processes in an enclosed environment and basis to design growth strategies depending on graphene targeted application
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