Influence of Ti doping on the performance of a ZnO-based photodetector

We study the influence of Ti doping on the photodetection properties of zinc oxide (ZnO) thin films. The pure ZnO and ZnO: 3% Ti (TZO) films were deposited on Si substrates by using DC-unbalanced magnetron sputtering. From the scanning electron microscopy (SEM) images, the TZO film grows more homogeneously in comparison with the pure ZnO structure. We suggest that Ti dopants play a role in uniformly distributing ZnO elements from the sputtering target to the Si substrate. The transmittance spectra of the Fourier transform infrared spectroscopy show a peak splitting of Zn-O stretching in the TZO film, which is also related to the dopant-modified film morphology. X-ray diffraction (XRD) spectra show that the Ti dopants also change the main ZnO crystal orientation from (0 0 2) to (1 0 3). The ZnO and TZO film-based photodetectors were fabricated by using a metal-semiconductor-metal planar configuration with Ag as the metal contact. Based on the I-V characteristics, Ti doping in the ZnO system reduces the dark current and induces the enhancement of the photo-to-dark-current ratio. Our study shows the important role of Ti doping on the improvement of photodetection performance.