Improved surface morphology and crystalline quality of semi-polar ([formula omitted]) AlN epilayer with dual moderate-temperature-grown AlN interlayers

Abstract

Semi-polar (112‾2) AlN epilayers have been grown on (101‾0) m-plane sapphire substrates with the help of dual moderate-temperature-grown (MTG) AlN interlayers by metal-organic chemical vapor deposition. Significant improvements in both surface morphology and crystalline quality of the semi-polar (112‾2) AlN epilayers have been achieved with the insertion of the MTG AlN interlayers due to the formation of nano-scale patterned substrate-like structure and the reduction in the basal-plane stacking faults with their associated partial dislocations. The effect of the variation in the thickness of the MTG AlN interlayer ranged from 20 to 100 nm was investigated in detail based on the characterization results of the atomic force microscopy (AFM) and X-ray diffraction. It was revealed that all the semi-polar AlN epilayer samples grown with the dual AlN interlayers on (101‾0) m-plane sapphire substrates were uniquely [112‾2]-oriented regardless of the variation in the thickness of the MTG AlN interlayer. Moreover, it was found that the most remarkable reduction in the surface roughness and the most effective improvement of structural quality could be obtained when the thickness for the inserted dual MTG AlN interlayers was approximately 80 nm. In fact, the smallest root mean square roughness of the semi-polar (112‾2) AlN epilayer surface was determined to be 1.4 nm by AFM measurement.