Improved transparent-conducting properties in N2- and H2- annealed GaZnO thin films grown on glass substrates

The effects of N2- and H2- annealing on the transparent-conducting properties of Ga-doped ZnO (GaZnO) were examined. The as-grown GaZnO thin film, which was deposited on a soda-lime glass substrate by r.f. magnetron sputtering, exhibited moderate transparent-conducting properties: a resistivity of ∼100 Ω·cm and an optical transmittance of ∼86%. After annealing in N2 or H2, the GaZnO samples showed great improvements in both the electrical and the optical properties. Particularly, in the H2-annealed sample, a dramatic decrease in the resistivity (7 x 10-4 Ω·cm) with a considerable increase in the carrier concentration (4.22 x 1021 cm-3) was observed. This is attributed to both an increase in the number of Ga-O bonds and a reduction in the number of chemisorbed oxygen atoms though H2 annealing. The sample revealed an enhanced optical transmittance (∼91%), which comes from the Burstein-Moss effect. Namely, a blue-shift of the optical absorption edge, which results from the increased carrier concentration, was observed in the H2-annealed sample. The results suggest that hydrogen annealing can help improve the transparent conducting properties of GaZnO via a modification of the electrochemical bonding structures.