Fabrication and characterization of high quality undoped and Ga2O3-doped ZnO thin films by reactive electron beam co-evaporation technique
Résumé
High-quality undoped and Ga2O3-doped ZnO thin films have been co-evaporated by reactive electron beam evaporation in an oxygen environment. The effect of the dopant on the structural, optical and electrical properties has been investigated. X-ray diffraction measurements have shown that the Ga2O3-doped ZnO films are c-axis-oriented and that the linewidth of the (0 0 2) peak is sensitive to the variation of the dopant concentration. The 28% Ga2O3-doped ZnO films showed the best crystallinity. The AFM images have shown that the surfaces of the Ga2O3-doped ZnO became smoother by raising the concentration of Ga2O3 in the fabricated films. Photoluminescence on 28% Ga2O3-doped ZnO reveals an enhancement of the near band edge ultraviolet emission at 380 nm while the intensity of the deep level emissions weakens. A reduction of the oxygen vacancies as well as the reduction of the zinc interstitials with gallium may explain this effect. Thus the possibility of transitions of electron in the conduction band to a deep acceptor level due to zinc interstitials may decrease. The optical band-gap energy increased with the rise of the dopant concentration. The electrical resistivity increased with the rising of the Ga2O3 concentration while the carrier concentration decreased which is due to chemisorptions of oxygen into the ZnO thin films. (c) 2004 Elsevier B.V. All rights reserved.