Semipolar (11-22) AlN templates prepared by pulsed hydride vapor phase epitaxy

Single-crystal semipolar (11-22) AlN templates are grown on 2 in. m-plane sapphire substrates via high-temperature hydride vapor phase epitaxy. Pulsed HCl and NH3 precursors are used separately to enhance Al mobility and reduce parasitic reactions, thereby improving the crystal quality of an AlN film. Compared with continuous growth, the FWHM (full width at half maximum) of the x-ray rocking curves of a (11-22) AlN film grown with pulsed HCl decreased from 882″ to 616″ along [11-23]AlN and from 684″ to 608″ along [1-100]AlN, indicating a significant reduction in the defect density of the AlN film. This improvement in crystal quality benefits from the prolonged Al mobility, which facilitates the transition of an AlN growth mode from 3D (three-dimensional) islands to a 2D (two-dimensional) step flow. However, the crystal quality of the film grown with NH3 pulses deteriorates, which may be due to the formation of subgrains with different crystal orientations caused by the long interruption of NH3. Based on the optimized growth conditions, a 7 μm-thick single-crystal (11-22) AlN film is prepared using HCl pulses, exhibiting smooth surface morphology with typical macrosteps, providing a substrate foundation for subsequent homoepitaxial AlGaN-based deep ultraviolet optoelectronic devices.