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

Abstract

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 (ε, σ, –Im ε−1 and ωp) 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 ∼ 1021 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.