Application of terahertz spectroscopy to analyze the crystalline properties of Cu2ZnSnS4 crystal

In this study, we successfully synthesized Cu₂ZnSnS₄ (CZTS) crystals and investigated their structural and vibrational properties using field-emission scanning electron microscopy (FE-SEM), field-emission electron probe microanalysis (FE-EPMA), X-ray diffraction (XRD), Raman spectroscopy, and terahertz (THz) spectroscopy. FE-SEM confirmed a smooth and well-defined surface morphology without significant crystalline disorders, while FE-EPMA analysis indicated a near-stoichiometric composition with slight Cu enrichment and Zn/S deficiencies. XRD analysis verified the kesterite crystal structure, which was further supported by Raman spectroscopy through the identification of key vibrational modes. THz spectroscopy provided additional insights into the phonon modes of CZTS, revealing several absorption peaks in agreement with theoretical predictions. The technique also allowed for the distinction of closely spaced peaks, identifying new absorption features not previously observed with Raman spectroscopy. Temperature-dependent THz measurements at 70 K demonstrated enhanced spectral resolution and peak shifts attributed to thermal expansion and phonon interactions. These findings confirm the kesterite structure of CZTS crystals. This study contributes to a deeper understanding of CZTS material properties, facilitating its application in photovoltaic and optoelectronic devices. • FE-EPMA shows near-stoichiometric CZTS with slight Cu-richness; XRD confirms the kesterite structure. • Raman spectra identify key vibrational modes, supporting assignment to the kesterite phase. • THz spectroscopy reveals new phonon absorptions and resolves closely spaced peaks not seen by Raman. • At 70 K, THz spectra sharpen and peaks shift, consistent with thermal contraction and anharmonic effects. • These results support CZTS materials characterization for photovoltaic and optoelectronic applications.