Investigation of the interrelation between the chemical state and the electric properties in Al-doped ZnO films

Abstract

Transparent conducting Al-doped ZnO (AZO) thin films were prepared on glass substrates by radio frequency magnetron sputtering in pure Ar. The influence of the annealing atmosphere on the microstructure, chemical state, electric and optical properties of the AZO films was investigated with X-ray diffraction, field-emission scanning electron microscopy, X-ray photoelectron spectroscopy and Hall measurements. The AZO thin films annealed under vacuum had the highest carrier concentration of 2.488 × 10²⁰ cm⁻³ and a Hall mobility of 16.35 cm² V⁻¹ s⁻¹, while the AZO thin films annealed in air had the lowest carrier concentration of 4.182 × 10¹⁷ cm⁻³ and a Hall mobility of 2.375 cm² V⁻¹ s⁻¹. The fitted narrow-scan O1s spectra revealed that O1s was composed of three components. The AZO thin films annealed under vacuum appeared to have a higher proportion of medium binding energy which correspond to O²⁻ ions in the oxygen-deficient regions within the ZnO matrix, and have a lower proportion of high binding energy component which correspond to loosely bound chemisorbed oxygen. It believed that the oxygen vacancies and chemisorbed oxygen of the films played an important role in the electrical conductance. The carrier concentration increased with the formation of oxygen vacancies. The Hall mobility increased with desorption of the loosely bound oxygen.