Investigation of cadmium-incorporated ZnO thin films for photodetector applications

Thin films of cadmium-incorporated ZnO (CZO) have been synthesized and investigated for potential light detecting applications. Epitaxial, c-axis oriented growth of CZO films was achieved using pulsed laser deposition technique. X-ray diffraction and atomic force microscopy analyses of the as-deposited CZO film were compared with those of undoped ZnO film in order to comprehend the effect of cadmium incorporation on the microstructural and electrical properties of ZnO. Hall measurements performed at 298 K revealed a high mobility of 169.26 cm2/V for the CZO film deposited on c-plane sapphire substrate. Non-alloyed contacts of indium (In) and aluminum (Al) were metalized on the film surface using thermal evaporation and current-voltage (I–V) measurements were made in the metal/semiconductor/metal (MSM) configuration at 298 K. While the In/ZnO/In device showed a linear I–V response, the In/CZO/In device exhibited non-linear and asymmetric I–V curves. Upon exposure to a UV light source of intensity 24 μW/cm2, this non-linearity was found to reduce significantly and a high photosensitivity of 175.9% and responsivity of 110.75 A/W was recorded for the In/CZO/In MSM device. The photoelectrical behavior of the Al/CZO/Al device was found to be consistently ohmic under both dark and illuminated conditions.