  The strain induced by lattice mismatch at the interface is responsible for
the different value of the band discontinuities observed recently for the
AlN/GaN (AlN on GaN) and the GaN/AlN (GaN on AlN) polar (0001) interface. We
present a first-principles calculation of valence band offsets, interface
dipoles, strain-induced piezoelectric fields, relaxed geometric structure, and
formation energies. Our results confirm the existence of a large
forward-backward asymmetry for this interface.
