High quality non-polar a-plane AlN template grown on semi-polar r-plane sapphire substrate by three-step pulsed flow growth method

•The non-polar a-plane AlN template with three-step pulsed flow growth method was successfully grown for the first time.•The crystalline quality, optical property, and surface morphology of the a-plane AlN sample SA3 were greatly improved.•A root mean square value as small as 3.4 nm was obtained for non-polar a-plane AlN template sample SA3. The structural and optical properties of the non-polar a-plane (112̅0) AlN template grown on semi-polar r-plane (11̅02) sapphire substrate with three-step pulsed flow growth method in a metalorganic chemical vapor deposition system were investigated extensively. It was found that the crystalline quality, optical property, and surface morphology of the a-plane AlN template grown by the three-step pulsed flow growth method featured with variable temperature were greatly improved as compared with the a-plane AlN template grown by conventional one-step pulsed flow growth method with a fixed temperature. In fact, besides the remarkably reduced full width at half maximum values of both the symmetrical X-ray rocking curve and the A1(TO) Raman scattering peak, strong relative light transmittance and steep absorption edge were observed in the ultraviolet-visible absorption spectrum for the a-plane AlN template grown by the three-step pulsed flow growth method. Furthermore, a superior surface morphology and a decreased surface deformation were achieved with a root mean square value as small as 3.4 nm in an atomic force microscope detection area of 5 × 5 µm2. These results reveal that the three-step pulsed flow growth method should be powerful to grow high crystalline quality non-polar a-plane AlN template which plays a crucial role in the epitaxial growth of the AlGaN-based III-nitrides.