Thickness effect on scaling law and surface properties of nano-dimensional SnTe thin films

SnTe is an important material because of its applications in mid-infrared photo-detectors. In the present work, the effects of film thickness on scaling law and surface properties (i.e., morphologies and optical properties) of SnTe thin films have been investigated. SnTe thin films of different thicknesses are prepared by means of e-beam evaporation technique. The surface morphology of each film is analyzed by atomic force microscopy (AFM) as well as a scanning electron microscope. The crystallinity of the films is found to increase with increasing film thickness, as confirmed by x-ray diffraction and Raman measurements. Fractal analysis is performed on AFM images to investigate the irregularity of surfaces. It is found that the surface of the thicker sample is rougher than the thinner sample. The autocorrelation function is applied to investigate the self-affine fractal nature of surfaces. The average roughness, interface width, lateral correlation length, local surface slope, and fractal dimension increased with film thickness. The values of roughness exponent, growth exponent, dynamic exponent, and steepening exponent are calculated and found to be alpha = 0.76 - 0.96, beta = 0.75, z = 1.92, and lambda = 0.35 - 0.25, respectively. The scaling exponents together with the other parameters such as the local surface slope indicate that the growth is quasi-3D island/mound type with rapid surface roughening behavior and obeys anomalous scaling. The multiple scattering cross sections of light together with Fourier transform infrared spectroscopy data analyses suggest that the higher crystalline film with a smaller number of defects is infrared-sensitive and may be more suitable for advanced mid-infrared detector applications.

Automated summary

The study investigates the effects of film thickness on scaling law and surface properties of SnTe thin films. It is found that crystallinity of the films increases with thickness, and the thicker sample has a rougher surface. Fractal analysis reveals irregularity of surfaces, with parameters indicating quasi-3D island/mound growth type with rapid roughening behavior and anomalous scaling. The results suggest that thicker, higher crystalline films may be more suitable for advanced mid-infrared detector applications.