Stability of the electro-optical properties and structural characteristics of H and Al co-doped ZnO films after heat treatment in H/Ar plasma

ZnO co-doped with Al and H (HAZO) films were exposed to H/Ar plasma for various durations (0-60 min) at 400 °C to study the effects of heat treatment in H/Ar plasma on the stability of the electro-optical properties and microstructure variations of the films. The crystallite size of the films slightly decreased from 29.6 nm to 26.3 nm when the H/Ar plasma treatment duration (Ta) was increased from 0 min to 30 min at 400 °C, and then decreased significantly to 13.8 nm when the duration was further increased to 60 min. The X-ray photoelectron spectroscopy spectra reveal a dramatic increase in the amount of oxygen-deficient regions and zinc interstitials for Ta values larger than 30 min. Transmission electron microscopy images show high-density basal-plane stacking faults (BSFs) in the films obtained with a Ta of 60 min at 400 °C. The secondary ion mass spectroscopy depth profiles show that the H concentration slightly decreased with increasing Ta up to 30 min. H was significantly out-diffused, enhanced by BSFs and grain boundaries, for Ta values larger than 30 min. The incorporation of H into oxygen vacancies suppressed the defect-induced vibration mode and the passivation of defect states in the as-deposited film; however, this passivation effect was gradually eliminated with increasing Ta. The resistivity of the films remained stable in the range of 5.8×10−4 Ω cm to 6.5×10−4 Ω cm as Ta was increased from 0 min to 30 min, and then increased with further increases in Ta. The electrical properties deteriorated due to a decrease in the crystallite size, high-density BSFs, and the out-diffusion of hydrogen. The figure of merit (ΦTC) was used to evaluate the performance of the electro-optical properties. The ΦTC decreased slightly from 3.32×10−2 Ω−1 to 1.61×10−2 Ω−1 when Ta was increased from 0 min to 30 min, and then decreased dramatically to 5.7×10−3 Ω−1 when Ta was 60 min.