Spectroscopic studies of the electronic structure of wurtzite GaN and Al_xGa_(1-x)N

摘要

The electronic structure of wurtzite GaN and Al_xGa_(1-x)N has been investigated using photoemission, soft x-ray emission, inverse photoemission, and soft x-ray absorption. A well-defined surface state below the valence band maximum has been measured using angle resolved photoemission for GaN(0001). This state is destroyed by the adorption of either H_2 or O_2. The state shows no dispersion, and has even symmetry with respect to the mirror planes of the surface. Plarization measurements indicate that it is of sp_z character, consistent with a dangling bodn state. Inverse photoemission indicates that there are no unoccupied surface states. The builk density of states of Al_xGa_(1-x)N was measured using soft x-ray absorption and emission. The motion of the elementally resolved bulk valence band maximum was measured as a function of Al-concentration, and the value of the bandgap bowing parameter for Al_xGa_(1-x)N measured to be zero.