1：Experimental Design and Method Selection:

The study used RF sputtering for AlN deposition on 6H-SiC substrates, followed by high-temperature face-to-face annealing (FFA) at 1700°C under N2 ambient. Metalorganic vapor phase epitaxy (MOVPE) was used for subsequent AlN growth on the annealed templates. Methods included atomic force microscopy (AFM) for surface morphology and X-ray diffraction (XRD) for crystalline quality assessment.

2：Sample Selection and Data Sources:

6H-SiC (0001) Si-face on-axis substrates with diameters of 2 inches and misorientation angles less than 0.5° were used. Substrates were chemically mechanically polished (CMP) and treated with buffered hydrofluoric acid and deionized water before sputtering.

3：5° were used. Substrates were chemically mechanically polished (CMP) and treated with buffered hydrofluoric acid and deionized water before sputtering. List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: Equipment includes an RF sputtering system with polycrystalline AlN target, N2 and Ar gases, a high-temperature annealing furnace, and an MOVPE system with trimethylaluminum (TMA) and ammonia (NH3) precursors. Materials include AlN films of varying thicknesses (20, 50, 100, 200, 400, 600 nm).

4：Experimental Procedures and Operational Workflow:

AlN films were deposited by RF sputtering at 600°C, 0.2 Pa chamber pressure, N2/Ar gas flow of 72/18 sccm, and 700 W RF power. Post-deposition annealing was performed at 1700°C for 3 hours under N2 at 1013 hPa. MOVPE growth was done at 1300°C, 13 kPa reactor pressure, and V/III ratio of 211. AFM and XRD measurements were conducted to analyze surface morphology and crystallinity.

5：2 Pa chamber pressure, N2/Ar gas flow of 72/18 sccm, and 700 W RF power. Post-deposition annealing was performed at 1700°C for 3 hours under N2 at 1013 hPa. MOVPE growth was done at 1300°C, 13 kPa reactor pressure, and V/III ratio of AFM and XRD measurements were conducted to analyze surface morphology and crystallinity. Data Analysis Methods:

5. Data Analysis Methods: XRD rocking curve full width at half maximum (XRC-FWHM) values were used to assess crystalline quality. Lattice constants were calculated from XRD reciprocal space maps (RSMs). AFM images were analyzed for surface roughness and step structures.