Electronic structure of diamond-like carbon

The electronic structure of amorphous diamond-like carbon is reviewed. Numerous calculations are giving a consistent description of the local atomic structure as containing small, mainly chain-like clusters of sp(2) sites, which control the band gap. The experimental optical gap of all types of DLC is found to depend primarily on their sp(2) content. Detailed analysis finds that all jr: states within the sigma-sigma* gap are all localized, so the mobility gap greatly exceeds the optical gap. This accounts for the photoluminescence excitation spectrum and the low carrier mobility seen in TFTs. Calculations also iind that the dangling bond defects tend to possess some s orbital character, lowering their energy level in the gap. These states pin the Fermi level and cause undoped ta-C and ta-C:H to be p-type. The paramagnetic defect is the dominant recombination centre and the ESR linewidth is attributed to exchange narrowing. (C) 1997 Elsevier Science S.A.