Impact of terbium inclusion on the photodetection performance of ZnO thin films

Abstract

Terbium (Tb)-doped ZnO thin films were fabricated using the successive ionic layer adsorption and reaction route. Their structural, morphological, optical, and ultraviolet photosensing properties were studied and compared with those of pure ZnO thin films. The x-ray diffraction results illustrate that the pure and Tb-doped ZnO films reveal hexagonal structures with the P63mc space group. The 1% Tb-doped ZnO film shows an increase in the absorption and a decrease in bandgap value from 3.24 eV to 3.15 eV compared to pure ZnO. The photoluminescence results reveal the existence of emission centers at 388, 414, 441, and 477 nm in the fabricated thin films. By increasing the rare earth (Tb) element, the near band edge emission was decreased and correspondingly increased the blue emission due to its 4f orbital energy transition. The photosensing parameters, such as responsivity, external quantum efficiency, and specific detectivity values of the 1% Tb-doped ZnO detector, are 2.21 × 10−1 A W−1, 75%, and 1.84 × 1010 Jones, respectively, which are higher compared to the other fabricated devices due to their better optoelectronic properties. For the 5% Tb-doped ZnO detector, the I–V characteristic curve shows a non-linear behavior, which indicates that a small Schottky barrier is formed in the detector due to widening of the potential barrier and depletion region by Tb. We also investigated the possible energy band diagram of both linear and non-linear (Schottky barrier) behaviors for Tb-doped ZnO detectors.