Luminescence of Silicon Nanoparticles Synthesized by Ion Implantation

Sammanfattning: Silicon nanoparticles (SiNPs) have been shown to display luminescence in the visible range with a peak wavelength depending on the nanoparticle size. This finding is of potential interest for integration of optoelectronic devices in semiconductor technology. In this thesis, silicon nanoparticles are formed in thermally grown SiO2 films by implantation of Si-ions. Implantation parameters such as energy, fluence, and target temperature, as well as post-implantation annealing (PIA) conditions are studied in order to optimize the luminescence properties of the nanoparticles. Ion energies between 15 and 70 keV, fluences up to 1017 atoms/cm2, and target temperatures ranging from room temperature to 600 ºC are employed. The PIA process is carried out at temperatures between 1000 and 1200 °C in ambient nitrogen, or argon gas. In addition, dangling bonds, which reduce the total luminescence of SiNPs, are passivated, using forming gas annealing (FGA). Quantification of hydrogen content induced by FGA process is performed by ion beam analysis (IBA) techniques. Furthermore, irradiations with swift heavy ions (SHIs) with several tens of MeV kinetic energy are performed as a possible way to further reduce the defect density. In particular, the relation between electronic and nuclear stopping for the defect production and annealing is investigated. The composition and physical structure of the samples are studied via IBA techniques, transmission electron microscopy (TEM), and grazing incidence X-ray diffraction (GIXRD). Based on the results from IBA, the implantation profiles are reconstructed. The physical structures of SiNPs revealed by TEM and GIXRD, furthermore, show that the high fluence implantation with an adequate PIA condition leads to the formation of crystalline SiNPs with a mean size of about 6 nm. The optical properties of SiNPs are characterized by photoluminescence (PL) techniques. After the implantation, only defect PL is present, but it is found that intense SiNP PL can be achieved for samples implanted with 15 atomic% excess peak concentration of Si in SiO2 and PIA at 1100 °C in argon gas for 90 minutes. Finally, an alternative way for fabricating SiNPs in SiO2 is tested, using oxygen implantation into a Si wafer. Although the PL from this experiment is less intense than the PL of SiNPs fabricated by the Si-implanted SiO2 route, the results are technologically interesting due to the convenience of the process.