Transparent and conducting p-type (CuS)x:(ZnS)1-x thin films produced by thermal evaporation: An efficient broadband Si heterojunction photodiode

This study demonstrates the viability of the thermal evaporation method to produce transparent and highly conductive p-type (CuS)x:(ZnS)1-x thin films by achieving the highest conductivity value (1.4 × 103 S/cm) reported in this field to date. This places it in direct comparison with n-type transparent conductors. Analysis through X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) unveils nanocomposite structures comprising sphalerite ZnS, chalcocite Cu2S, and covellite CuS nanocrystals in the thin films. The study reveals that transmittance values at a wavelength of 550 nm vary from 84 % to 65 % based on the increasing CuS ratio, establishing thermal-evaporated (CuS)x:(ZnS)1-x thin films as promising candidates for p-type transparent electrodes. Moreover, p+-(CuS)0.49:(ZnS)0.54/n-Si heterojunction photodiodes were also produced. The heterojunction diode exhibited excellent photo-response characteristics in a wide range of wavelengths between 325 and 1170 nm at zero-bias. The responsivity value of the photodiode was as high as 1.44 A/W at the peak wavelength of 912 nm (9.45 mW/cm2) with a high Ion/Ioff ratio of 1.45 × 104. Besides, it was shown to have excellent detectivity, response time, and external quantum efficiency (EQE) values corresponding to 2.62 × 1012 Jones, 8.45 µs, and 244 %, respectively. Most of these values are superior to those even in commercial-grade photodiodes.