Analysis on different detection mechanisms involved in ZnO-based photodetector and photodiodes

The present study reports on the comparison between the ultraviolet (UV) light detection mechanisms in ZnO-based photodetectors and ZnO/PEDOT:PSS hybrid photodiodes. Using spray pyrolysis method, ZnO thin films were deposited upon glass substrates. The deposition temperature was varied from 350 to 425 degrees C and the physical properties of ZnO thin films were investigated. The structural analysis reveals that all the prepared ZnO thin films have a preferred orientation along the (002) plane with hexagonal wurtzite structure. The morphological analysis reveals that the grains are uniformly distributed. Electrical properties reveal that the ZnO thin film deposited at 425 degrees C shows a higher carrier concentration of 3.76 x 10(16) cm(-3) with low electrical resistivity value of 2.59 x 10(2) ohm cm. For fabrication of UV photodetectors, the optimum ZnO layer with good electrical and optical property was deposited on ITO substrate with substrate temperature maintained at 425 degrees C. For the fabrication of hybrid UV photodiodes, poly (3,4 ethylene dioxythiophene):poly (styrene sulphonate) (PEDOT:PSS) and zinc oxide (ZnO) was used as the hole and electron transporting layers, respectively. The current-voltage (I-V) and photoresponse switching characteristics under UV light of the fabricated ZnO-based photodetector and photodiodes were studied and the detection mechanisms of such devices were analysed. It was observed that the ZnO-based photodiodes show higher photoresponsivity (R) value of 0.25 A/W with fast photoresponse switching speed.