Optical and electrical properties of very thin chromium films for optoelectronic devices

Establishing the optimal experimental conditions for the development of transparent metal contacts to be used in optoelectronic devices, such as organic light-emitting diodes and solar cells, is an important task. In this paper we present an overview of the development of very thin e-beam-deposited chromium films with high optical transparency. The surface morphology is investigated by scanning electron microscopy. The variation is examined of the films' electrical and optical properties (transmittance and complex refractive index) with the variation of the thickness and deposition rate. We observed that, for a given thickness of the chromium films, the absorption coefficient increases when the deposition rate is decreased. We also found that the thin films with a thickness of less than 10 nm show an average transmittance exceeding 60 % in the spectral range 400 – 1500 nm. The films' resistivity, ρ, is determined by the four-point probe method. The value of ρ varies in the range of 10−3 -10−4 Ω cm for chromium coatings in the thickness interval 5 – 100 nm. The results obtained show that very thin metal films could be an alternative to the transparent conductive oxides.