Atomically smooth surfaces with linearly aligned atomic steps in AlGaN layers grown using sputtered AlN template with reduced compressive strain on low misorientation off-angle sapphire substrates

Abstract Atomically smooth surfaces with linearly aligned atomic steps in AlGaN layers were demonstrated by the sputtered AlN template with reduced compressive strain using sapphire substrates with 0.2° misorientation off angle. The hillock structures owing to spiral growth were absent on the surfaces of Al 0.72 Ga 0.28 N and Al 0.80 Ga 0.20 N. In both samples, atomic force microscopy (AFM) images revealed atomically smooth surfaces with a root mean square roughness of approximately 0.2 nm, and aligned atomic steps. Furthermore, hillock formation owing to spiral growth was confirmed in Al 0.54 Ga 0.46 N. The X-ray diffraction (XRD) ω scan for the 0002 reflection showed that AlGaN maintained high orientation property to the c-axis direction of AlN. The best full width at half maximum achieved in this study were 13 and 15 arcseconds for Al 0.80 Ga 0.20 N and AlN, respectively. These results indicate XRD and AFM measurements were correlated. Furthermore, correlations were observed using transmission electron microscopy.