Adjustment of the selenium amount during ion beam sputtering deposition of CIS thin films

CuInSe₂ (CIS) films were prepared by ion beam sputtering depositing Cu, In and Se layers sequentially on BK7 glass substrates and annealing the 3-layer film in the same vacuum chamber. The adjustment of the Se amount in the film was achieved by controlling the sputtering time of the Se target. X-ray diffraction pattern shows CIS films have chalcopyrite structure and preferential (112) orientation when the sputtering of the Se layer is between 60 and 180 min. It also can be seen that the most intense and narrow peak indicates the highest crystallinity for the sample with sputtering Se of 60 min, which is in agreement with the Raman measurement. The content of Cu, In and Se in the film deviates from 1, 1 and 2 with increasing the sputtering time of the Se target. Direct band gap energy between 0.96 and 1.05 eV, depending on the Se amount, and a high absorption coefficient of 10⁵ cm⁻¹ are found. The measured film resistivities vary from 0.01 to 0.05 Ω cm. Thus, the structural, optical and electrical characteristics of the CIS thin films were dependent on the Se amount during the fabrication of films and after fitting the sputtering time of Se, an optimization of the properties and a saving of Se consumption were achieved.