Nature of disorder and localization in amorphous carbon

The electronic structure of amorphous diamond-like carbon is studied. Analysis of the participation ratio shows that pi states within the sigma-sigma* gap are localized. The localization arises from dihedral angle disorder. The localization of pi states causes the mobility gap to exceed the optical gap, which accounts for the low carrier mobility and the flat photoluminescence excitation spectrum. (C) 1998 Elsevier Science B.V. All rights reserved.