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 Cu2ZnSnS4 (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 degrees C. These films show p-type semiconducting behaviour with a carrier concentration similar to 10(17) cm(-3), optical absorption coefficient similar to 10(4) cm(-1) and direct optical band gap similar to 1.4 eV. At higher substrate temperatures (>= 350 degrees C), secondary phases of Cu2-x S and SnS2 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 degrees C. The observed higher band gap for CZTS films deposited at 400. C has been attributed to the growth of the Cu2-x S and SnS2 secondary phase and a sulfur-poor CZTS phase. The activation energy of the CZTS thin film deposited at 325 degrees C is 15meV.