Growth and characterization of CT(S,Se) thin films and Al/n-Si/p-CT(S,Se)/Mo heterojunction diode application employing a two-stage process

Abstract

Cu2SnS3 (CTS), Cu2Sn(S,Se)3 (CTSSe), and Cu2SnSe3 (CTSe) thin films were deposited on n-type silicon wafer substrates using a two-stage process. This process involved drop-coating Cu-Sn precursors, which is different from the vacuum-based fabrication methods. The sulfurization/selenization of the films was achieved using the rapid thermal processing (RTP) method at 550 °C. The structural, morphological, and optical properties of CTS, CTSSe, and CTSe thin films were investigated. Al/n-Si/p-CTS/Mo, Al/n-Si/p-CTSSe/Mo, and Al/n-Si/p-CTSe/Mo heterojunction diodes were formed, and electrical characterizations were performed. According to the performed analyses, it was detected that while CTS and CTSSe thin films had a Cu-poor chemical composition (Cu/Sn∼1.7), the CTSe thin film showed a Cu-rich chemical composition. X-ray diffraction (XRD) and Raman spectra of the samples showed that all samples had a monoclinic crystal structure as a dominant phase. Scanning electron microscope (SEM) images showed that the incorporation of selenium (Se) into prepared samples contributes to form a larger-grained structure. The band gap (Eg) of CTS, CTSSe, and CTSe thin films was determined from the optical reflectance measurements, and they were found to be 1.02 eV, 1.00 eV, and 0.96 eV, respectively. According to the data obtained from the I-V measurements of the heterojunction diode, the incorporation of Se into the film structure reduced the series resistance (Rs) in the heterojunctions from 8.27 × 102 Ω to 2.42 × 102 Ω, and the best ideality factor value was obtained in the Al/n-Si/p-CTSe/Mo heterojunction with a n = 2.87 value.