Influence of thermal treatment duration on the morphological and optical properties of a-IGZO

In this paper, the influence of post deposition annealing duration on the radio frequency (RF) magnetron sputtered amorphous InGaZnO4 (a-IGZO) thin films in terms of the morphological and optical properties has been studied. The correlations between the refractive index, optical bandgap and the surface morphology, as well as the film thickness and the stress in response to the annealing duration are established. The surface morphologies of IGZO thin films obtained from field-emission scanning electron microscopy (FESEM) reveal changes in the particle size. The particles grow larger with increasing annealing duration from 2 to 8 h. The root-mean-square (RMS) surface roughness of the IGZO films acquired from the atomic force microscopy (AFM) shows an increasing trend as the annealing duration is increased. The transmittance spectra of the films, obtained within the 200-2000 nm spectral range have been analysed using Swanepoel method to calculate the refractive index and optical thickness of IGZO. The calculated refractive index of the IGZO film shows an abrupt decrease from 2.151 to 2.044 at 632.8 nm and the optical bandgap slightly expands after the film has undergone thermal annealing for 2 h, but the refractive index gradually increases back to 2.164 and the optical bandgap redshifts with longer annealing duration. The thickness of IGZO layer estimated by the Swanepoel method shows a good agreement with the values measured from FESEM cross-section.

Automated summary

This paper investigates the effect of post deposition annealing duration on the morphological and optical properties of RF magnetron sputtered amorphous InGaZnO4 (a-IGZO) thin films. The study establishes correlations between refractive index, optical bandgap, surface morphology, film thickness, and stress in response to annealing duration. The results show that the surface morphology and particle size of IGZO films change with increasing annealing duration, while the refractive index and optical bandgap are also affected.