Fabrication and characterization of ternary Cu8SiS6 and Cu8SiSe6 thin film layers for optoelectronic applications

Abstract

We have fabricated and characterized Cu8SiS6 and Cu8SiSe6 thin film layers for optoelectronic applications. The layers were fabricated using a two step process by first evaporating a bilayer of Cu/Si on a Mo/glass substrate, followed by an anneal at temperatures in excess of 480°C in a H2S or H2Se containing atmosphere. Different process conditions with different Cu starting layer thickness, different H2S partial pressure and different anneal temperatures and times were evaluated. The best fabricated layers were thin polycrystalline layers with a relatively low amount of secondary phases. Relatively intense photoluminescence signals with a full width at half maximum of about 150meV could be measured on the samples with a peak position of 1.84 and 1.33eV for the Cu8SiS6 and Cu8SiSe6 materials respectively. The absorption coefficient of the Cu8SiS6 layer was determined from absorption and reflection measurements and was larger than 104cm−1 at energies above 1.8eV. Solar cells could not be fabricated so far, because the material appears to be very highly doped, leading to large ohmic leakage behavior in the fabricated solar cell structures.