We have observed six-bilayer periodic structures in GaN grown on GaAs(001).
The periodicity occurs along the zinc-blende(ZB)-A direction, suggest
ing that it originates from stacking faults on close-packed planes. GaN gro
wn on GaAs includes both ZB and wurtzite phases as a result of formation of
stacking faults and the periodic structures are mostly located between the
se two crystalline phases. Based on this observation, possible layer stacki
ng sequences are proposed, which are classified as 6H polytypes. (C) 2000 A
merican Institute of Physics. [S0003-6951(00)00303-X].