Point-defects-induced band edge displacements and band-gap narrowing in CdIn2O4 thin films

Transparent conducting oxides CdIn2O4 thin films were prepared by radio--frequency reactive sputtering from a Cd--In alloy target in Ar+O2 atmosphere. By transmission spectrum and Hall measurement for different samples prepared at different substrate temperatures, it could be found that the carrier concentration would increase with the decrease of substrate temperature, but absorption edge showed an abrupt variation from a blue shift to a red shift. Theoretically, the paper formulated the effect of high--density point defects on band structures; it embodied the formation of band tailing, Burstein--Moss shift and band--gap narrowing. The density of holes will influence the magnitude of optical band gap and transmittance of light. Since extrapolation method does not fit degenerate semiconductor materials, a more accurate method of obtaining optical band gap is curve fitting. In addition, ionized impurities scattering is the main damping mechanism of the free electrons in CdIn2O4 films, the density of ionized impurities induced by altering substrate temperature will affect the carriers mobility.