Fabrication and Structural and Optical Properties of Amorphous Si/SiO2 Superlattices on (100) Si

Abstract

ABSTRACTWe report the growth and characterization of amorphous Si (a-Si)/SiO2 superlattices on (100) Si. The a-Si layers (thickness varying from 1 to 10 nm) were vacuum-deposited at room temperature by molecular beam epitaxy while the SiO2 layers (1 nm) were grown by an ex-situ UV-ozone treatment. This procedure was repeated six times to produce periodic multilayer structures. The chemical modulation of these structures was confirmed by transmission electron microscopy and depth profiling using Auger electron spectroscopy. X-ray specular reflectivity showed that the structures have a well defined periodicity. The a-Si layers have a density approaching (>95 %) that of c-Si and an interfacial roughness that increases with the a-Si layer thickness. The Raman spectrum from the Si layers of all samples shows broad peaks near 150, 310 and 470 cm−1 that are typical of a-Si. On annealing at high temperatures, the three Raman bands decrease in intensity, while the 470 cm−1 band also shifts to higher frequency and becomes narrower. After annealing for 30 s at 1100 °C, the a-Si bands are weak and the 470 cm−1 band is merging with the c-Si 520 cm−1 line, indicating that partial re-crystallization of the Si layers has occurred. The room temperature light emission properties of these nanostructures in the green to red wavelength region is reported. The luminescence shifts to longer wavelength with increasing a-Si layer thickness, consistent with a quantum confinement mechanism.