Abstract

A crucial challenge in the optoelectronics industry is the realization of cheap and reliable transparent electrodes, i.e. films that permit to bring electrical current or potentials in proximity of optically active regions without significant loss of optical energy. The state of the art solution lies in large band gap semiconductors heavily doped with metals, known as transparent conductive oxides (TCOs), including indium tin oxide (ITO) [1]. Metal films, when sufficiently thin (<10 nm), become transparent to light, still maintaining continuity, thus having good electrical properties. We will show that, with respect to ITO, ultrathin metal films (UTMFs) can possess similar levels of transparency in the visible range, larger UV and IR transmittance and larger electrical conductivity [2, 3]. Figure 1 shows three-dimensional AFM image of Ni 10 nm film. RMS roughness and a peak-to-valley level were found to be 0.3 and 1.7 nm, respectively, both being well below deposited thickness. Figure 2 shows the transmission spectra of ultrathin Ni films of various thicknesses compared to 100 nm ITO film, confirming that electrodes made of ultrathin Ni films have wider spectrum of transparency compared to ITO. In particular their transparency is similar in the visible and larger in the UV and mid-IR ranges. Similar results have also been obtained with Cr.

© 2009 IEEE