30.11.2021
Improvements have been made in the polymer-assisted sublimation growth technique (PASG, based on PTB patent) by spin deposition of a series of well-defined polymer solutions on various SiC substrates. The optimized process is highly efficient and enables excellent reproducibility of high-quality epitaxial monolayer graphene used for quantum Hall effect (QHE) devices in electrical resistance metrology.
Compared to previous polymer deposition techniques, the polymer adsorbate is now deposited by spin-deposition of highly diluted solutions. This approach optimizes the stabilization of the substrate surface during growth and suppresses giant step bunching on a broader range of wafer substrates.
During the high-temperature sublimation process, it is essential that a smooth, homogenous, and continuous buffer layer forms at the interface of the substrate below the monolayer graphene. Precisely controlling and adjusting the amount of the adsorbed polymer by spin deposition for each wafer type decides the final monolayer graphene coverage and quality. In our comparison of absolute polymer concentrations, we found that wafers with small miscut angle of the same polytype need a higher polymer concentration than wafers with large miscut angle to obtain the same graphene quality.
Apart from the very smooth graphene layer needed to fabricate quantum Hall resistance standards (see Figure), the optimized technique also enables growing other graphene-based nanostructures such as graphene nanoribbons, different terrace widths, and heights that may be needed for other applications.
Figure: The foreground left shows microscopic images of graphene layers grown on different substrate wafers using the optimized method. In the foreground on the right, the microscopic image of particularly smooth monolayer graphene for the fabrication of quantum Hall resistance standards is shown.
Department 2.6 „Electrical Quantum Metrology“