Nd-YAG Ns-Pulsed Laser Induced Structural and Compositional Modification of Silicon Surface: Formation of Photoluminescent A-Si Nanostructures

This paper reports on the effect of laser irradiation of second harmonic of Q switched high power Nd: YAG laser onto the polished silicon (Si) wafers in air. Scanning Electron Microscope (SEM) images shows three distinct surface structures in the focal area of laser irradiation. Raman spectra reveal that the central region consists of crystalline Si (c-Si), the intermediate region consists of nano-crystalline Si (nc-Si) as well as amorphous Si (a-Si) and the outer peripheral region consists of a-Si embedded in silicon oxide (SiO₂) matrix. The presence of different percentage of oxygen in intermediate and peripheral regions of the irradiated spot is confirmed by Energy Dispersive X-ray (EDX) spectra. The outer peripheral region of the irradiated region appearing whitish and dominated by oxygen showed photoluminescence (PL) in far red region with twin peaks. The first PL peak at 1.75 eV is due to a-Si spherical nanostructures of average particle size of 5 nm. The second PL peak at 1.94 eV is more intense and is originated because of non-bridging oxygen hole center (NBOHC) defects.