High-quality GaN thin film deposition at low temperature by ECR plasma-assisted sputter deposition method and its dependence of sapphire substrate misorientation angle

Gallium nitride (GaN) thin films were deposited by electron cyclotron resonance (ECR) plasma-assisted sputtering, which combines GaN-magnetron sputtering with argon and nitrogen plasma assistance using an ECR high-density plasma. GaN films on the misorientation-angle-0.0° (just) sapphire substrate showed very good crystallinity with a GaN(0002) rocking curve (XRC) full width at half maximum (FWHM) of 0.042° and epitaxial growth confirmed by φ-scan measurements at a low heating temperature of 350 °C. However, the GaN thin film had a rough surface with circular grains about 100 nm in diameter and a surface root-mean-square height (Sq) of 1.21 nm. Therefore, the misorientation angle of the sapphire substrate was varied from 0.2° to 10.0°. As a result, the grains observed on the just substrate disappeared at 0.5°. The film had Sq: 0.33 nm, and the FWHM of the XRC of GaN(0002) was 0.066°, indicating improved surface flatness while maintaining crystallinity. This is considered to be due to the step flow, which promotes ECR plasma-assisted diffusion on the terrace even at the low temperature of 350 °C. The polarity of the GaN thin film was analyzed by time-of-flight atomic scattering surface analysis and found to be N-polar on all substrates.