High-quality CdS_xSe_1−x thin films with tunable bandgap for optoelectronic applications: growth by pulsed laser deposition and characterization

Abstract Although anionic variation allows for bandgap tuning in ternary compounds, there is still work to be done to obtain highly crystalline materials with optimal optical properties. In this study, binary and ternary CdS x Se 1−x (0 ≤ x ≤ 1) thin films were successfully synthesized on quartz substrates via pulsed laser deposition (PLD) using a Nd:YAG laser (1064 nm). The targets were prepared by mixing high-purity CdS and CdSe powders in proportions based on their molecular weights, followed by compaction. Film deposition was carried out under high vacuum (4 × 10 −6 Torr) at a substrate temperature of 500 °C. The resulting films are morphologically homogeneous and exhibit excellent crystallinity, with a strong preferential orientation along the (002) plane and hexagonal structure confirmed by x-ray diffraction (XRD). Raman spectroscopy revealed the simultaneous presence of LO-CdS and LO-CdSe phonon modes in the ternary films, with their intensities and positions varying with sulfur content. Optical transmittance measurements showed that the bandgap (Eg) ranges from 1.7 eV (CdSe) to 2.4 eV (CdS), with intermediate values for the ternary samples. Photoluminescence analysis demonstrated narrow, composition-dependent emission bands, enabling precise color tuning from red to green at room temperature. These results highlight the potential of PLD-grown CdS x Se 1−x films for optoelectronic applications that demand highly crystalline materials with customizable optical properties.