Growth of silicon quantum dots by oxidation of the silicon nanocrystals embedded within silicon carbide matrix

Abstract

A moderately low temperature (≤800 °C) thermal processing technique has been described for the growth of the silicon quantum dots (Si-QD) within microcrystalline silicon carbide (μc-SiC:H) dielectric thin films deposited by plasma enhanced chemical vapour deposition (PECVD) process. The nanocrystalline silicon grains (nc-Si) present in the as deposited films were initially enhanced by aluminium induced crystallization (AIC) method in vacuum at a temperature of Tv = 525 °C. The samples were then stepwise annealed at different temperatures Ta in air ambient. Analysis of the films by FTIR and XPS reveal a rearrangement of the μc-SiC:H network has taken place with a significant surface oxidation of the nc-Si domains upon annealing in air. The nc-Si grain size (DXRD) as calculated from the XRD peak widths using Scherrer formula was found to decrease from 7 nm to 4 nm with increase in Ta from 250 °C to 800 °C. A core shell like structure with the nc-Si as the core and the surface oxide layer as the shell can clearly describe the situation. The results indicate that with the increase of the annealing temperature in air the oxide shell layer becomes thicker and the nc-Si cores become smaller until their size reduced to the order of the Si-QDs. Quantum confinement effect due to the SiO covered nc-Si grains of size about 4 nm resulted in a photoluminescence peak due to the Si QDs with peak energy at 1.8 eV.