Structural, Optical, and Electrical Properties of Hafnium–Aluminum–Zinc-Oxide Films Grown by Atomic Layer Deposition for TCO Applications

Krajewski M., Tokarczyk M., Świętochowski P., Wróbel P., Kamińska M. and Drabińska A.

ACS Omega

8(33), 2023, 30621-30-629, 10.1021/acsomega.3c04256

ZnO is a widely studied material that exhibits versatile doping possibilities. Most research presents singly doped ZnO, leaving the potential of codoping unexplored. Within this study, hafnium–aluminum codoped zinc oxide (HAZO) thin films were grown on a glass substrate using the atomic layer deposition technique at 200 °C. A comprehensive analysis of the surface morphology and electrical and optical properties of the samples was conducted for varying the Al/Hf doping ratio. X-ray diffraction studies showed that the obtained films are polycrystalline, exhibiting a preferential growth direction along the (1 0 0) plane without any detectable precipitates. Moreover, the electrical measurements of HAZO films revealed that they exhibit lower resistivity (∼9.5 × 10–4 Ωcm) than the commonly used aluminum zinc oxide films (AZO). This improvement can be primarily attributed to the promotion of the n-type carrier concentration to 4.45 × 1020 cm–3 while maintaining a mobility value equal to 14.7 cm2/Vs. The doping also influences the optical properties of the material by widening the band gap and changing the refractive index, as observed by spectroscopy and ellipsometry studies. These findings highlight the potential of proposed HAZO thin films for future applications in electronic devices utilizing transparent conducting oxides.