Band discontinuities in zinc-blende and wurtzite AlN/SiC heterostructures

The AlN/SiC band discontinuities in zinc-blende (110), (111), and wurtzite (0001) heterostructures were examined using the ab initio pseudopotential approach. At the nonpolar AlN/SiC(110) junction, we find a valence-band offset of 1.7 eV. At the polar heterojunctions the band alignment depends on the interface composition, and valence-band offsets as high as 2.5 eV are obtained for neutral interfaces with an Al/Si mixed plane and as low as 1.3 eV with a N/C mixed plane. Atomic relaxation plays a major role in determining the offset. The structural change from cubic (111) to hexagonal (0001) heterojunctions affects predominantly the conduction-band offset, and has only a minor influence on the valence discontinuity.