Preparation and characterization of nitrogen doped ZnO films and homojunction diodes

Abstract

Nitrogen-doped ZnO (ZnO:N) films were prepared by the reactive magnetron sputtering technique using a zinc target. The effect of thermal annealing in different ambient on the films composition, chemical bonding states, structure, optical transmittance and photoconductivity was investigated. The as-grown films are composed from 9-nm large grains with strained unit cell. The annealing process relaxes the strain and increases the grain size to 39 nm. Annealing also increases the direct band gap of the film from 2.42 eV to 3.26 eV. The as-grown and annealed films show photoconductivity in the visible region which is partly due to the effect of a nitrogen-related defect level with the ionization energy of 1.71 eV. The conversion of the as-grown n-type films to p-type ZnO was achieved by annealing the films in air. The converted p-ZnO and electrodeposited n-ZnO films were used in the fabrication of light-emitting homojunction diodes. Diodes with a reasonably good current-voltage rectification factor exhibited electroluminescence property in the ultraviolet-visible region. From the junction capacitance of these diodes the density of holes in p-ZnO films grown on stainless steel substrates was determined as 1.5x1017 cm-3.

Keywords

• Composition
• homojunction
• optoelectronic
• XPS
• ZnO:N