Carrier Control in Polycrystalline ZnO:Ga Thin Films via Nitrogen Implantation

• Published in: ECS journal of solid state science and technology 2012-01, Vol.1 (5), p.P237-P240
• Main Authors: Shtereva, K. S., Novotny, I., Tvarozek, V., Vojs, M., Flickyngerova, S., Sutta, P., Vincze, A., Milosavljevic, M., Jeynes, C., Peng, N.
• Format: Article
• Language: English
• ISSN: 2162-8769; 2162-8777
• DOI: 10.1149/2.003206jss

The electrical characteristics of gallium-doped zinc oxide (ZnO:Ga) thin films prepared by rf diode sputtering were altered via nitrogen implantation by performing two implants at 40 keV and 80 keV with doses of 1×1015 and 1×1016 cm−2 to achieve a p-type semiconductor. An implantation of 1×1015 cm−2 N+-ions yielded a p-type with hole concentrations 1017-1018 cm−3 in some as-implanted samples. The films annealed at temperatures above 200°C in O2 and above 400°C in N2 were n-type with electron concentrations 1017-1020 cm−3. The higher nitrogen concentration (confirmed by SRIM and SIMS), in the films implanted with a 1×1016 cm−2 dose, resulted in lower electron concentrations, respectively, higher resistivity, due to compensation of donors by nitrogen acceptors. The electron concentrations ratio n(1×1015)/n(1×1016) decreases with increasing annealing temperature. Hall measurements showed that 1×1016 cm−2 N-implanted films became p-type after low temperature annealing in O2 at 200°C and in N2 at 400°C with hole concentrations of 3.2×1017 cm−3 and 1.6×1019 cm−3, respectively. Nitrogen-implanted ZnO:Ga films showed a c-axes preferred orientation of the crystallites. Annealing is shown to increase the average transmittance (>80%) of the films and to cause bandgap widening (3.19-3.3 eV).