Enhancement (100 times) of photoluminescence in pulsed laser deposited ZnO thin films by hydrogen ion implantation

Abstract

Owing to its wide bandgap (3.37eV) and a large exciton binding energy (60meV), fabrication of ZnO based optoelectroincs devices is a very active research area. Hence, enhancing the photoluminescence of the ZnO films will be important to achieve higher efficiency optoelectronic devices. Hydrogen ion implantation (Energy = 50keV, Dose = 5×10¹²cm^-2) have been performed on Pulsed Laser Deposited ZnO thin films deposited at 650°C. The samples were subsequently subjected to Rapid Thermal Annealing at 750°C, 800, 850°C and 900°C for 30 seconds in oxygen environment. X-ray Diffraction study confirms deposition of highly oriented <002> ZnO films for all the samples. However, the peaks for the samples are not at the same position due to the strain induced during implantation and subsequent annealing. Low temperature photoluminescence (8K) spectra of the samples revealed the presence of peaks of donor-bound exciton (D°X) and free-exciton (FX) at 3.36eV and 3.37eV respectively. Deep level defect peak around 2.5eV was also observed in the samples but the intensity of these peaks was substantially weaker than the near band edge (NBE) peaks verifying the high quality of the films. Moreover, the integrated PL peak intensity of the NBE show that the luminescence gets considerably enhanced as the samples are implanted (4 times) and subsequently annealed (up to 100 times) when compared with the as-deposited sample. Thus, implanting hydrogen ions maybe a good way to enhance the photoluminescence and thus efficiency for ZnO based devices.