Stress-induced surface characterization by wavelet and fractal analysis in Ga-doped ZnO thin films

The Ga-doped ZnO (GZO) were deposited by magnetron reactive sputtering on glass substrates at room temperature with different deposited times to obtain various thickness. The root-mean-square (RMS) roughness obtained from the atomic force microscopy (AFM) images is observed to shift linearly with the deposited time, the fractal geometry and multi-resolution signal decomposition (MRSD) based on wavelet transform were applied on the surface profiles and the results does not synchronously changes as the thickness, which is related to the profile’s frequency. The calculated compressive in-plane stress of highly c-axis oriented GZO films also shows an irregular variation as the increase of film thickness, what’s more, the in-plane stress and fractal dimension exhibit a polynomial relationship and the two parameters can be used for describing the surface morphology.