Research on FTO/CBD-CdS: Cl thin film photodetector with a vertical structure

In this work, CdS thin films were deposited on glass/fluorine-doping tin oxide (FTO) substrates by low-cost chemical bath deposition (CBD), followed by annealing with CdCl2-doping (Cl-doping) to fabricate resistive-type photodetectors (PDs) with a vertical structure of glass/FTO/CBD-CdS:Cl/electrode. The effect of annealing with Cl-doping (AwCl) on the various properties of films and the photodetection performance of PDs were systematically characterized by special testing methods. The results revealed that the surface morphology and crystal structure of CBD-CdS:Cl films were improved, accompanied by an enhancement of hexagonal phase (002) crystal plane (wurtzite structure), and the optical bandgap of films can be adjusted between 2.43 and 2.26 eV while the electron activation energy of the films was reduced from 75.9 to 10.3 meV after AwCl. Furthermore, the light responsivity of CBD-CdS:Cl PDs were 0.57, 0.59 and 1.67 A/W under 365, 400 and 530 nm illumination at a bias of −2.0 V, respectively, and the detectivity of photons at corresponding wavelengths were 3.7 × 108, 3.9 × 108 and 1.08 × 109 Jones. Meanwhile, the PDs showed optimized repeatability and improved sensitivity under periodic illumination. The above results demonstrated that the CBD-CdS:Cl PDs with a vertical structure developed in this work had good detection performance at certain characteristic wavelengths.