Temperature dependent photoreflectance study of Cu_2SnS_3 thin films produced by pulsed laser deposition

摘要

The energy band structure of Cu_2SnS_3 (CTS) thin films fabricated by pulsed laser deposition was studied by photoreflectance spectroscopy (PR). The temperature-dependent PR spectra were measured in the range of T= 10-150 K. According to the Raman scattering analysis, the monoclinic crystal structure (C1cl) prevails in the studied CTS thin film; however, a weak contribution from cubic CTS (F-43m) was also detected. The PR spectra revealed the valence band splitting of CTS. Optical transitions at E_A = 0.92 eV, E_B = 1.04 eV, and E_c = 1.08 eV were found for monoclinic CTS at low-temperature (T= 10K). Additional optical transition was detected at E_A~C = 0.94eV, and it was attributed to the low-temperature band gap of cubic CTS. All the identified optical transition energies showed a blueshift with increasing temperature, and the temperature coefficient dE/dT was about 0.1 me V/K.