Preparation, optical, and vibrational properties of nanocrystalline silicon

Microcrystalline silicon nanoparticles were prepared by thermal annealing a-Si:H/a-SiO{dollar}sb{lcub}x{rcub}{dollar}:H multilayers. Transmission electron microscopy studies show that the multilayer structure is intact during annealing processes. The thermally grown microcrystalline silicon nanoparticles are randomly oriented and have dimensions nearly equal to the amorphous silicon layer thickness, as confirmed by X-ray diffraction and dark-field transmission electron microscopy. Since the layer repeat distance in a-Si:H/ a-SiO{dollar}sb{lcub}x{rcub}{dollar}:H multilayers can be controlled to atomic layer resolution we expect the size of the microscrystalline silicon particles grown using our technique to be more uniform than those prepared by conventional methods.; In studies of size related effects in microcrystalline materials the particle size distribution has caused many problems in the interpretation of results. The motivation for this work is to investigate the size induced effects with the narrower microcrystallite size distribution expected from the multilayer annealing approach. The possibility of electronic quantum confinement effects for microcrystalline silicon embedded in amorphous matrix is also explored by photomodulation experiments.; Our experimental results show that size effects in both cases are masked by other effects. In Raman scattering experiments were observed that a large stress contributes to a significant Raman peak shift. In photomodulation experiments a broad band photo-induced absorption is observed which signifies that amorphous phase dominates the spectrum.; In this study the optical transmission measurements are performed to extract the crystallized volume fraction in the {dollar}mu{dollar}c-Si/a-Si composite system. The results are compared with the values deduced from Raman scattering experiments. The advantages and disadvantages of different characterization techniques are discussed.; Raman scattering studies of porous silicon prepared by electrochemical etching show a broad and down-shifted Raman peak. A large size distribution of the porous silicon particle is inferred. The photoluminescence spectrum of porous silicon reveals that there could be more than one source responsible for photoluminescence from our porous silicon samples.