Improved transparent-conducting properties in N ₂- and H ₂-annealed GaZnO thin films grown on glass substrates

The effects of N ₂- and H ₂-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 ~10° Ω-cm and an optical transmittance of ~86%. After annealing in N ₂ or H ₂, the GaZnO samples showed great improvements in both the electrical and the optical properties. Particularly, in the H ₂-annealed sample, a dramatic decrease in the resistivity (7 × 10 ^-4 Ω-cm) with a considerable increase in the carrier concentration (4.22 × 10 ²¹ 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 H ₂ 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 H ₂-annealed sample. The results suggest that hydrogen annealing can help improve the transparentconducting properties of GaZnO via a modification of the electrochemical bonding structures.