Enhanced UV sensing of ZnO films by Cu doping

We have investigated structural, optical, and electrical properties of ZnO:Cu films deposited by ultrafast spray technique at 450 degrees C for 30 s. Cu concentration in the ZnO system was varied from 0 at.% to 2.5 at.%, as detected by X-ray fluorescence spectroscopy. From the structural analysis, X-ray diffraction patterns show that (100), (002), and (101) planes are observed in pure ZnO. By inserting a Cu concentration of 2 at.% or higher, the (100) and (101) planes entirely disappear, and the crystal is strongly oriented in (002) plane. The average grain size of the films increases from 113.6 nm to 155.8 nm by increasing the Cu content, as observed by scanning electron microscopy. Furthermore, current-voltage (I-V) characteristics show that the 1.5 at.% Cu concentration has the highest UV sensitivity. Such behavior may be originated from carrier trapping under the dark and de-trapping under ultraviolet illumination, as analyzed using UV-Vis, photoluminescence, and FTIR spectroscopy techniques. This interesting result will be confirmed through optical properties analysis. This result is important for the development of a mass scale UV detector based on ZnO film with short fabrication time and improved functionality.