Homogeneity improvement of N-polar (000-1) InGaN/GaN multiple quantum wells by using c-plane sapphire substrate with off-cut-angle toward a-sapphire plane

To improve the homogeneity of the N-polar (000-1) (%c-plane) InGaN/GaN multiple quantum wells (MQWs) grown by metalorganic vapor phase epitaxy (MOVPE), the growth of GaN and MQW on two c-plane sapphire substrates with an off-cut angle of 0.8° toward the a-plane (sub-A) and the m-plane (sub-M) was performed. The effects of the off-cut direction on the structural properties and surface morphologies of %c-plane GaN films were elucidated. It was found that the step bunching and meandering of %c-plane GaN were significantly suppressed on sub-A. The spatial homogeneity of the %c-plane InGaN/GaN MQWs along the off-cut direction was observed in the submicrometer scale using microbeam X-ray diffraction. By inhibiting the step bunching of the GaN template using sub-A, the thickness homogeneity of the MQWs on sub-A has been significantly improved in comparison with that on sub-M.