Stable vicinal step orientations in m-plane GaN

• Morphological evolution of MOCVD template growth on miscut m-plane GaN.
• The faces of on-axis m-plane pyramidal hillocks exhibit a- and a+c step directions.
• –c-miscut and a-miscut templates form diagonal striations with a±c step directions.
• Pure c-direction steps are not observed for any miscut or growth condition.
• Quantum wells grown on a+c miscut substrates exhibit redshift and narrow linewidth.

The performance of InxGa1−xN-based m-plane LEDs and laser diodes grown by metalorganic chemical vapor deposition on bulk GaN substrates is currently limited by lower indium uptake and inhomogeneous linewidth broadening in the blue spectrum compared to semipolar planes and c-plane. Linewidth broadening is partially attributed to inhomogeneous indium composition that is associated with template morphology. We investigate the morphological evolution of homoepitaxial GaN growth on bulk m-plane substrates in three co-loaded miscut orientations: nominally on-axis, 1° in the –c-direction (–c-miscut), and 1° in the a-direction (a-miscut). Atomic force microscopy reveals four-sided pyramidal hillocks for on-axis growth with faces inclined toward the [112¯0]a-axis (a-faces) and the [0001] c-axis (c-faces). The a-faces exhibit steps oriented in an a+c direction with longer terrace widths than the c-face steps. The –c-miscut template growth sometimes forms diagonal striations, characterized by regions with stable a+c step direction. The a-miscut template growth exhibits meandering steps oriented in the a±c directions that bunch to form diagonal striations. These results reveal that c-direction steps are unstable compared to a±c directions. We further demonstrate that m-plane GaN substrates with combined a+c miscut lead to narrower InxGa1−xN photoluminescence emission spectra in blue with enhanced indium incorporation.