RF-Magnetron Sputtered Kesterite Cu₂ZnSnS₄ Thin Film Using Single Quaternary Sputtering Target Prepared by Sintering Process

Cu₂ZnSnS₄ (CZTS) thin film applicable to an absorber material in compound thin film solar cells was deposited by a single quaternary sputtering target containing four components—Cu, Zn, Sn, and S—and its material properties were investigated. A single quaternary sputtering target was fabricated by sequential powder mixing/ball milling, pressure moulding, and a sintering process. An asfabricated pellet or sputter target sintered at 500 °C–700 °C showed relevant peaks associated with CZTS phases. However, acceptable density as a sputter target (> 90% of ideal density) was attained up to a sintering temperature of only 500 °C due to thermal expansion. Unlike other metallic precursor approaches, there was no volume expansion after sulfurization. The sulfurized CZTS film contained CZTS phases including some secondary phases such as SnS or SnS₂ depending on the film thickness. This result was attributed to the different sputtering yields of the constituents in the sputter target. Optical E_g decreased with increasing deposition time. The E_g attained was 1.488 eV, well-matched to the reported CZTS data. The carrier concentration, resistivity, and mobility of the CZTS film were 1.29 × 10¹⁷ cm⁻³, 1.2 × 10⁻¹ Ω·cm and 5.44 cm⁻³/V·sec, respectively, showing suitability for absorber layer applications.