  We present a comprehensive study on metal-organic vapor phase epitaxy growth
of N-polar and Al-polar AlN on 4H-SiC with 4 deg miscut using constant growth
parameters. At a high temperature of 1165 degC, N-polar AlN layers had high
crystalline quality whereas the Al-polar AlN surfaces had a high density of
etch pits. For N-polar AlN, the V/III ratio below 1000 forms hexagonal
hillocks, while the V/III ratio over 1000 yields step bunching without the
hillocks. 1-um-thick N-polar AlN layer grown in optimal conditions exhibited
FWHMs of 307, 330 and 337 arcsec for (002), (102) and (201) reflections,
respectively.
