AlGaN/GaN MBE heterostructures: polarization effects and their implication on electronic properties

The origin of the strong polarization fields in nitride heterostructures is discussed by comparing the symmetry properties of zincblende and wurtzite structures. Some peculiar effects in nitride heterostructure electronic properties, induced by the polarization fields are considered, like the determination of the valence band offset by x-ray photo emission spectroscopy (XPS) and the formation of 2D electron gases in AlGaN/GaN. The Fermi level position at MBE GaN, AlGaN and AlN surfaces has been measured in-situ by XPS. The role played by surface states has been emphasized, experimentally and through self consistent calculations.