Speaker
Shyama Rath
(Department of Physics, Faculty of Science, Chulalongkorn University, Bangkok 10330, THAILAND; Department of Physics and Astrophysics, University of Delhi, Delhi-110007, INDIA)
Description
The wide bandgap semiconducting oxide, ZnO is attractive for a range of optoelectronic devices due to its dual advantages of high optical transparency and electrical conductivity. In view of its applications, ZnO films have been grown by a variety of techniques and different methods of material engineering have been used to tailor its properties. In this study, we show the effect of varying oxygen partial pressure on the optical properties of rf-sputtered ZnO films. A set of films were obtained for varying argon pressures of 0.025, 0.03, 0.05, 0.075, and 0.1 mbar. The films were subsequently annealed at 400ºC in an oxygen atmosphere. X-ray diffraction and Raman spectra of the films confirmed the wurtzite structure and a good crystalline quality. The as-deposited films were strained and which relaxed after annealing. Atomic force microscopy was used to monitor the surface topography and the surface roughness before and after annealing.
The reflectivity spectra of the films showed a decrease in the number of interference fringes with an increase in argon pressure. This is representative of the increase in thickness of the films. The values of the thickness, refractive index, absorption co-efficient and carrier concentration of the films for varying argon pressures are further determined spectroscopic from ellipsometry measurements by analysing the complex dielectric function (ε (E) = ε$_1$(E) + iε$_2$(E)) in the range of 0.5-5.5 eV and using appropriate optical models. The refractive index of the films decreases from 1.859 to 1.794 when the argon pressure is increased from 0.015 and 0.1 mbar.
The bandgap is investigated by photoluminescence spectroscopy and did not exhibit any significant change with argon pressure. However, the bandgap of the as-deposited film showed a blueshift as compared to the annealed film. A widening of the optical bandgap is due to a high carrier concentration induced by non-stoichiometry and explained by the Burstein-Moss shift.
Primary author
Shyama Rath
(Department of Physics, Faculty of Science, Chulalongkorn University, Bangkok 10330, THAILAND; Department of Physics and Astrophysics, University of Delhi, Delhi-110007, INDIA)
Co-authors
Chaman Singh
(Department of Physics and Astrophysics, University of Delhi, Delhi-110007, INDIA)
Reena Goyal
(Department of Physics and Astrophysics, University of Delhi, Delhi-110007, INDIA)
Sojiphong Chatraphorn
(Department of Physics, Faculty of Science, Chulalongkorn University, Bangkok 10330, THAILAND; Research Centre in Thin Film Physics, Thailand Centre of Excellence in Physics, CHE, Bangkok 10400, THAILAND)
