Ion beam assisted fortification of photoconduction and photosensitivity

A new approach to substantially improve UV/Visible photo sensitivity of nanocrystalline CdS (nc-CdS) thin films is investigated. nc-CdS thin films grown on Si wafer by pulsed laser deposition followed by irradiation treatment were used to fabricate photo-sensors. Swift heavy ion irradiation (SHII) of the nc-CdS thin films was carried out using 70 MeV 58Ni6+ ions. The influence of irradiation fluence on the transport behaviour of nc-CdS is investigated by device performance under the illuminating light of wavelengths 355 nm, 405 nm and 470 nm. Indeed, the sensors presented here are easy to fabricate without requirement of rigorous synthesis procedure. Moreover, they illustrate characteristics similar to those of photo-sensors designed with complex structures and tedious procedures. The improvement in conductivity under the exposure of SHII is a consequence of enrichment in carrier concentration as reveals from current-voltage (I-V) measurements. The sensor exhibits improvements in the response time, responsivity, photosensitivity, quantum efficiency, and specific detectivity as a function of both the ion fluence and illuminating light wavelength. These sensors show superior value of all device parameters under the illumination wavelength 470 nm of visible light. The utmost values achieved for responsivity, sensitivity, external quantum efficiency, and specific detectivity are ∼ 82 A/W, 1.02 × 103 %, 19.5 × 103 %, and 5.05 × 1011 cm Hz1/2W−1 respectively under same illumination at 5 V for 1 × 1013 ions/cm2 irradiated photosensor. Under the same illumination, bias voltage and irradiation fluence the minimum value achieved for rise time and fall time is 183 ms and 61 ms respectively. A possible mechanism involved in both the SHII and illumination wavelength induced moderation of conductivity and consequently photosensitivity is explained on the basis of variation in the defect densities.