Low-temperature growth of CuS thin film on flexible substrates for photodetection

Abstract

The covellite phase of copper sulfide thin film (CuS), owing to its excellent electronic, optical, and chemical properties, has attracted enormous attention in cutting-edge research. This research work emphasizes a comprehensive study of structural, optical, morphological, and electrical properties of CuS thin film deposited by chemical bath deposition (CBD) technique on flexible polyethylene terephthalate (PET) substrate at different deposition temperatures, i. e. 25 °C, 40 °C, 55 °C, and 70 °C for fabrication of flexible photodetector. XRD and Raman studies depict presence of hexagonal covellite phase (CuS), where as the RMS roughness of CuS thin film increases with a rise in deposition temperature. The optical bandgap of CuS thin film gets reduced with a rise in deposition temperature. The optimized CuS thin film, deposited at 70 °C, has exhibited a homogeneous surface with RMS roughness of 13.72 nm, mobility of 25.09 cm2/Vs, and bandgap of 1.86 eV. The mobility of CuS thin film is found to be increased with the rise in deposition temperature. The flexible CuS photodetector, deposited at 70 °C, has shown better photoresponse characteristics, exhibiting the highest responsivity of 0.18 mA/W, detectivity of 1.39×108 Jones, and sensitivity of 173.25 % upon light illumination. The photocurrent established possesses an outstanding dependence on various intensities of illuminated light. Furthermore, the bending test of flexible CuS photodetectors reveals the absence of any sign of deterioration up to a bending angle of 30°. The CuS thin film-based photodetector device exhibits the optimized photodetector device with reproducibility and steady photoresponse after bending. This suggests that the Al/CuS-PET/Al photodetector device could be used in various wearable optoelectronic device applications.