Valence-band offsets and different band-gap behaviors of (beta-GaN)/(beta-AlN) superlattice and (alpha-GaN)/(alpha-AlN) superlattice

The valence-band offsets at (beta-GaN)/(beta-AlN) (001), (110), (111) interfaces and strained (alpha-GaN)/(alpha-AlN) (0001) interface are determined systematically by ab initio calculations using supercells of up to (6+6) layers, and by an average bond energy model. The results are in very good agreement with experimental data. It is found that the variation of the band gap in (alpha-GaN)(n)/(alpha-AlN)(n) (0001) system with n is completely different from that in the (beta-GaN)/(beta-AlN) system. These different band-gap behaviors are shown to be related to the internal electric fields in alpha-GaN and alpha-AlN slabs, which are induced by the difference of the spontaneous polarizations in these slabs. (C) 1996 American Institute of Physics.