Investigation of time-dependent stability and surface defects in sol–gel derived IGZO and IZO thin films

In the present work, we investigated the thin film properties, stability, and surface defects of various compositions of indium gallium zinc oxide (IGZO) and indium zinc oxide (IZO) thin films. The thin films of IGZO and IZO were obtained through the solution processing route and deposited using the spin coating technique. All films were found to be amorphous with roughness below 2.0 nm. Further, it was established that the introduction of gallium helps in controlling the electrical resistivity and stabilizing the amorphous phase of IGZO films. The time-dependent study of IGZO and IZO thin films reveals that the films remain structurally stable for one month. However, a slight change in the morphology can be seen after 13 days. The films which seem to be uniform and smooth under an optical microscope also contain few dark spots as well. These dark spots upon close investigation using atomic force microscopy (AFM) and electron probe microscope analyzer (EPMA) reveal that they are the part of films themselves, stand in a vertical position, and the composition on these spots is high in indium content. Simultaneously, the measured composition of the spot-free surface is always less in indium content in comparison to the expected composition. In this study, our findings predict that in the case of solution-processed IGZO and IZO thin films there is a possibility of movement of indium ions to form a surface defect, which in turn can lead to the poor performance of IGZO and IZO based devices. Highlights Effect of compositional change on thin film properties of solution-processed IGZO and IZO thin films. Time-dependent stability of solution-processed IGZO and IZO thin films. Types of surface defects appearing in solution-processed IGZO and IZO thin films. Compositional analysis on the surface defects. Morphological analysis of surface defect.