Absorption and reflection analysis of transparent conductive Ga-doped ZnO films

Transparent conductive films of 2 at% Ga-doped ZnO films were prepared on C-plane sapphire substrates by e-beam evaporation in vacuum. The optical absorption, reflectance, structural and electrical properties of 2 at% Ga-doped ZnO films were investigated. The films are highly transparent (> 80 %) in visible-NIR ranges, and the optical bandgap exhibits a blue shift for the as-deposited films from 3.30 eV to 3.83 eV and for heat treatment from 3.27 eV to 3.60 eV for 2 at% Ga-doped ZnO films with respect to pure ZnO films. Through resistivity, optical constants (epsilon, sigma, -Im epsilon(-1) and omega(p)) and carrier concentration obtained from reflectivity and transmittance spectra for 2 at% Ga-doped ZnO films, we found that these films behave as n-type semiconductors exhibiting high carrier concentration N similar to 10(21) cm(-3). This also gives an opportunity to predict electrical behaviour of transparent conductive films on the basis of the analysis of absorption and reflection measurements.