Optical dielectric constant inhomogeneity along the growth axis in ZnO-based transparent electrodes deposited on glass substrates

Abstract

Simple optical measurements using a conventional spectrometer have revealed that in heavily doped ZnO films deposited on glass, the optical dielectric constant is inhomogeneous along the growth axis. Analyses based on Drude’s model have suggested that the origin of this inhomogeneity is the shorter carrier scattering time τc in the portion in contact with the glass substrate, while τc in the major portion of the films has been estimated to be as long as 1×10−14 s at infrared frequencies. This may imply that if better crystallinity is achieved in the initial stage of film deposition, higher conductivity will be attainable without sacrificing the high transparency of the electrode-on-glass system. In addition, the analyses have disclosed the correlation between the high transparency of the major portion of the films and the frequency dependence of τc that is caused by the dopants (Ga or Al) and makes τc even longer at visible-light frequencies.