Effect of annealing temperature on optical band-gap of amorphous indium zinc oxide film

Highlights: → The IZO films maintained the amorphous structure even after annealing at 300 deg. C. → All the IZO films had the high carrier concentration (>1019 cm-3) after annealing. → The renormalization did not play significant role in band-gap shifting. → The optical band-gap shift behaved as if only the BM effect is prevalent. - Abstract: The effect of annealing temperature on the electrical and optical properties of indium zinc oxide (IZO) (In2O3:ZnO = 90:10 wt.%) thin films has been investigated. The IZO thin films were deposited on glass substrates by radio frequency magnetron sputtering and then subjected to annealing in a mixed ambient of air and oxygen at 100, 200 and 300 deg. C. All the IZO films were found to have amorphous structure. With the increase of the annealing temperature, the carrier concentration decreased and the resistivity increased. The average transmittance of IZO thin films decreased slightly with annealing temperature. Interestingly, a systematic reduction of the optical band-gap from 3.79 eV to 3.67 eV was observed with annealing temperature. The change in optical band-gap was observed to be caused predominantly by Burstein-Moss band-gap widening effect suggesting unusual absence of band narrowing effect. The effects on optical and electrical properties of IZO films have been discussed in detail.