Grain size dependent optical band gap of CdI2 films

The thermally evaporated stoichiometric CdI2 films show good c-axis alignment normal to substrate plane for film thickness up to 200 nm, The optical absorption data indicate an allowed direct interband transition across a gap of 3(.)6 eV in confirmation with earlier band structure calculations, However, part of the absorption data near band edge can be fitted to an indirect band gap of 3 eV. The dependence of band gap on film thickness (> 200 nm) can be explained qualitatively in terms of decreasing grain boundary barrier height with grain size.