Effect of Cr, N co-doping on the structural and optical properties of ZnO thin films deposited by pulsed laser deposition

ZnO as a wide-band-gap semiconductor is widely used in optoelectronic and electronic devices owing to its excellent electrical and optical characteristics that can be tuned by doping with dopants. In this study, the Cr, N co-doped ZnO films were fabricated on sapphire substrates using the pulsed laser deposition technique, and the structure and optical properties of the films were studied extensively. The structural and valence state characterizations indicate that the films are single-phase hexagonal ZnO structure with preferred c -axis orientation, but more incorporation of Cr in the films will degrade the crystal quality of the materials; Cr and N dopants substitute Zn and O ions of the ZnO host lattice existing as Cr 3+ and N 3− in the film, respectively. The resistivity of the films significantly increases by co-doping with Cr and N. Optical characterization reveals that the absorption edge of the films shifts to higher energy with increasing Cr content. The results indicate that the observed increase in band-gap energy of the Zn 1− x Cr x O/N films may be attributed to the decrease in the lattice constant, which is a consequence of the strain, determined by the amount of Cr and N in the film deposition process.