Low temperature crystallization of Cu₂ZnSnSe₄ thin films using binary selenide precursors

In the present paper, a novel process for synthesis of Cu₂ZnSnSe₄ thin films via low temperature selenization (350 °C) of multiple stacks of binary selenides has been reported. Further, the influence of selenization temperature (250–450 °C) on the physical properties of Cu₂ZnSnSe₄ thin films was studied and discussed herein. The Rietveld refinement from X-ray diffraction data of Cu₂ZnSnSe₄ films grown at a selenization temperature of 350 °C was found to be single phase with kesterite type crystal structure and having lattice parameters a = 5.695 Å, c = 11.334 Å. Raman spectra recorded using multi excitation wavelength sources under non-resonant and near resonant conditions confirms the formation of single phase Cu₂ZnSnSe₄ films. Secondary ion mass spectroscopic (SIMS) analysis demonstrated that composition of elements across the thickness is fairly uniform. Energy dispersive X-ray analysis measurement reveals that the obtained films are Cu-poor and Zn-rich. The scanning electron micrographs of binary selenide stacks selenized at a temperature of 350 °C shows randomly oriented cylindrical grains. The optical absorption studies indicated a direct band gap of 1.01 eV. The films showed p-type conductivity with electrical resistivity of 4.66 Ω cm, Hall mobility of 15.17 cm² (Vs)⁻¹ and carrier concentration of 8.82 × 10¹⁶ cm⁻³.