1：Experimental Design and Method Selection:

Nonpolar a-plane GaN films were directly grown on titanium patterned sapphire substrates (Ti-PSS) by metalorganic chemical vapor deposition (MOCVD).

2：Sample Selection and Data Sources:

A 5 nm-Ti film was deposited on the 2 inch R-plane sapphire substrate by electron beam evaporation, followed by a standard photolithography to form hole-arrays pattern.

3：List of Experimental Equipment and Materials:

Trimethylgallium (TMGa), trimethyaluminum (TMAl) and ammonia (NH3) were used as Ga, Al and N sources, respectively.

4：Experimental Procedures and Operational Workflow:

After annealing in H2 at 1180 °C, a 1.5 nm thick AlN wetting layer was deposited on the Ti-PSS. Then, a 10 nm thick composition-graded AlxGa1?xN intermediate layer, with the Al composition changing from one to zero, was grown at 1170 °C. Finally, a two-step growth process with different V/III ratios and reactor pressures was adopted.

5：5 nm thick AlN wetting layer was deposited on the Ti-PSS. Then, a 10 nm thick composition-graded AlxGa1?xN intermediate layer, with the Al composition changing from one to zero, was grown at 1170 °C. Finally, a two-step growth process with different V/III ratios and reactor pressures was adopted. Data Analysis Methods:

5. Data Analysis Methods: The surface morphologies of the a-plane GaN films were characterized via AFM. The crystalline quality was evaluated by examining the X-ray rocking curve-full width at half maximum (XRC-FWHM). Scanning electron microscopy (SEM), asymmetric X-ray diffraction (XRD) reciprocal space maps (RSMs) and room temperature Raman scattering measurements were carried out to illustrate the XRD broadening mechanisms of the two samples.