Macroscopic polarization and band offsets at nitride heterojunctions

Ab initio electronic structure studies of prototypical polar interfaces of wurtzite III-V nitrides show that large uniform electric fields exist in epitaxial nitride overlayers, due to the discontinuity across the interface of the macroscopic polarization of the constituent materials. Polarization fields require a nonstandard evaluation of band offsets and formation energies: we find a large strain-induced asymmetry of the offset [0.2 eV for AlN/GaN (0001), 0.85 eV for GaN/AlN (0001)], and tiny interface formation energies.