Order-disorder control of Si nanoparticles in laser-irradiated amorphous-Si thin film

Abstract

Ordering of Si nanoparticles formed on an amorphous-Si thin film via laser irradiations was examined in terms of laser fluences, incident angles, and polarizations. The Si nanoparticles were created through two-dimensional scans of an ultraviolet nanosecond laser with a Gaussian beam. The arrangements of the nanoparticles varied significantly depending on the polarization at off-normal incidence. To perform quantitative analysis, an edge detection algorithm (the Hough transform method) was used to extract the nanoparticle size and position data from secondary electron microscopy images, and the nanoparticle distribution and ordering were estimated through the pair-correlation function. At normal incident angle, the Si nanoparticles were well ordered along the polarization direction, whereas for off-normal incidence at 30°, the Si nanoparticles were significantly disordered at polarization angles below 90° (out-of-plane) but ordered at the polarization angle of 90°. These features were interpreted in terms of the Rayleigh anomaly condition and competition between two wave vectors at off-normal incidence. The features can be applied to control the device performance in substrates for electronic or photovoltaic devices via nanoparticle ordering.