1：Experimental Design and Method Selection:

Er-doped AlN thin films were prepared on (0001) sapphire substrates by radio frequency (RF) reactive magnetron sputtering. The target was a

2：6-mm-diam pure ErAl alloy target (Al:

1 Er = 95:5 at. %). The substrates were cleaned ultrasonically in alternate baths of acetone, alcohol and deionized water. The chamber was first evacuated to a vacuum of 4×10-4Pa and then heated to 100℃ for 1 hour to remove the residual water vapor. After that,

3：99% argon was inlet as working gas while 999% nitrogen is reaction gas. The target was pre-sputtering for 3min each time to remove the oxide layer before sputtering Er-doped AlN thin films with the same parameters of sputtering. Sample Selection and Data Sources:

The substrates were (0001) sapphire substrates.

4：List of Experimental Equipment and Materials:

The crystal structure of the films was investigated by X-ray diffraction (XRD, Bede D1). The surface of the thin film was measured by SEM (SEM, INCA PentaTETx3). Stylus profiler (Dektak XT) was used to measure the thickness of the films. Piezoelectric response and surface roughness were measured by piezoelectric response force microscopy and atomic force microscopy (PFM, AFM, SPA-300HV), respectively. The resistivity of the thin films was measured by the standard ferroelectric test system (Radiant Precision LC 2000).

5：1). The surface of the thin film was measured by SEM (SEM, INCA PentaTETx3). Stylus profiler (Dektak XT) was used to measure the thickness of the films. Piezoelectric response and surface roughness were measured by piezoelectric response force microscopy and atomic force microscopy (PFM, AFM, SPA-300HV), respectively. The resistivity of the thin films was measured by the standard ferroelectric test system (Radiant Precision LC 2000). Experimental Procedures and Operational Workflow:

4. Experimental Procedures and Operational Workflow: The films were deposited at different sputtering times (60,75,90,105,120 minutes).

6：Data Analysis Methods:

The relationship between the crystal orientation, surface morphology, piezoelectric properties, and resistivity of the films and the sputtering time was analyzed.