Si implantation in SiO2: Stucture of Si nanocrystals and composition of SiO2 layer

摘要

Silicon is known to be a poor light emitter. However, once in nanometer scale, it can emit a strong visible and infrared light after excitation. Si nanocrystals (Si-nc) with a diameter of similar to 3 nm are produced by implantation of Si ions into amorphous SiO2 followed by thermal annealing. These Si-nc could allow the use of Si for making luminescent devices compatible with optoelectronic integrated circuits. Si ions have been implanted with an energy of 5 0 and 100 keV to fluences ranging from 2 x 10(16) to 3 x 10(17) Si/cm(2). The effect of Si implantation fluence on the microstructure of the Si-nc and the SiO2 matrix has been examined using TEM and XPS. The size, spatial distribution and concentration of the Si-nc have been investigated by TEM and compared to the depth distribution of implanted Si ions. A crystalline structure of the Si-nc has been observed for local Si concentration in excess larger than similar to 3 x 10(21) Si/cm(3). Moreover, defects (twins, SF's) and faceting have been observed by HRTEM in Si-nc larger than 6 nm. These large Si-nc are produced with a local Si concentration in excess larger than similar to 1 x 10(22) Si/cm(3). XPS has revealed the presence of an oxygen poor surface layer in the SiO2. This effect of oxygen depletion is also visible in TEM over a layer of similar to 25 nm. (C) 2007 Elsevier B.V. All rights reserved.