Structural and optical properties of CZTS thin films deposited by ultrasonically assisted chemical vapour deposition

Ultrasonically assisted chemical vapour deposition has been used for the deposition of thin films of Cu 2 ZnSnS 4 (CZTS) on glass substrates. The effect of substrate temperature on the structural and optical properties of thin films has been investigated. The CZTS films show a tetragonal structure with preferential orientation along the (1 1 2) plane. X-ray diffraction and Raman studies confirm the formation of a single-phase CZTS film at a deposition temperature of 325 °C. These films show p-type semiconducting behaviour with a carrier concentration ∼10 17 cm −3 , optical absorption coefficient ∼10 4 cm −1 and direct optical band gap ∼1.4 eV. At higher substrate temperatures (⩾350 °C), secondary phases of Cu 2− x S and SnS 2 also start growing along with the CZTS phase. The band gap of CZTS films increases from 1.40 to 1.50 eV as the deposition temperature increases from 325 to 400 °C. The observed higher band gap for CZTS films deposited at 400 °C has been attributed to the growth of the Cu 2− x S and SnS 2 secondary phase and a sulfur-poor CZTS phase. The activation energy of the CZTS thin film deposited at 325 °C is 15 meV.