Enhancement of Mobility of CuS Thin Film on PET Substrate Grown by Chemical Bath Deposition Method For Flexible Photodetectors
摘要
The covellite phase of copper sulfide (CuS) thin film is deposited on a flexible polyethylene terephthalate (PET) substrate by an economical, low-cost chemical bath deposition (CBD) method with varied molar concentrations of CuSO4 and Na2S2O3 and varying annealing temperature. Post-deposition characterisations of CBD-deposited CuS thin film have been performed to investigate the structural, morphological, optical, and electrical properties of CuS thin film. The crystallinity of CuS thin film is increased with an increase in molar concentrations of CuSO4 and Na2S2O3 and increased annealing temperature, as depicted by x-ray diffraction (XRD) and Raman spectroscopy. The bandgap and resistivity of p-type CuS thin film are decreased with an increase in the molar concentration of precursors and with the effect of post-deposition annealing treatment. The mobility of CuS thin film is improved from 5.47 cm2/V·s to 25.43 cm2/V·s with an increase in molar concentration of CuSO4, whereas it is increased from 5.47 cm2/V·s to 31.77 cm2/V·s with an increase in molar concentration of Na2S2O3. Post-deposition annealing treatment has significantly enhanced the mobility of CuS thin film from 31.77 cm2/V·s to 74.82 cm2/V·s due to an increase in average grain size. The CuS thin film annealed at 110°C exhibits higher mobility (74.82 cm2/V·s) with a larger average grain size of 79 nm, indicating improved grain connectivity with fewer grain boundaries, and charge carrier movement. It further enhances photoresponse due to efficient light carrier absorption, thereby reducing the resistivity. The CuS thin film-based flexible photodetector deposited at 70°C with 0.1 M CuSO4, 0.5 M Na2S2O3, and annealed at 110°C possesses a responsivity of 0.29 mA/W and specific detectivity of 2.01 × 108 Jones due to enhanced mobility, which makes it suitable for low-cost cutting-edge flexible photodetector applications.