Study On The Microstructure And Optical Properties Of Rare-earth Doped Nc-Si

Silicon is an important material of solid state electronics and microelectronic industry. It is known that bulk silicon is not an efficient optical source due to its indirect band gap and the competition of non-radiative recombination. Silicon is the second most abundant element in the earth’s crust. It is cheap and stable. The technology is mature. It is useful to improve the optical properties of silicon-based materials. It’s a promising way to introduce rare earth elements into silicon-based materials because of their abundant energy bands. Erbium has an optical transition at1.54μm which is transparency window used for fiber optic communication systems. Cerium can emit ultraviolet/blue light. Erbium-doped and cerium-doped nc-Si materials are studied in this paper, respectively.All samples studied in this paper were prepared by ion-beam sputtering and ion implantation. Samples were wet oxidized and then annealed in different conditions. The microstructure was studied by TEM. Optical properties were observed.1. Er-doped samplesNanostructure silicon, of which the size is about5nm and without obvious microstructure defects, is successfully found by TEM.As is shown in PL spectra, the emission around750nm is attributed to nc-Si. Its intensity increases as annealing time rises, and reaches its highest value when annealed with one minute. This is because the number of nc-Si clusters becomes larger and non-radiative centers become smaller. When the annealing time is more than one minute, the nc-Si clusters are so large that the quantum effect is weakened. So the intensity decreases and red shift happens.The emission around1533nm. shown in PL spectra, is attributed to Er3+ions duc to4I132→4I152transition. The relationship with emission intensity around1533nm and annealing conditions is contrary to the emission around750nm, which indicates a competition between nc-Si emission and Er3+ions emission. According to PLE spectra, emissions at400nm and800nm are obversed. Emission at400nm is attributed to band gap transition of nc-Si. Meawhile, emission at800nm is attributed to radiative recombination of restricted excitons in nc-Si.Peak around520cm-1shown in Raman spectra is attributed to nc-Si. The tendency of intensity is the similar to that of the peak around750nm shown in PL spectra when annealing conditions changes. The diameter of nano-cluster is calculated. The calculation result is7.2nm which is similar with that observed by TEM.2、Ce-doped samplesAs is found from the PL spectra, there is a broad PL band attributed to Ce ions. There are three peaks around364nm,425nm and500nm. PL intensity increases with Ce concentrations and reaches its highest value when Ce concentration is1.2at%. The PL peak value is almost linear with Ce concentrations.PL intensity increases with the increase of annealing temperature and reaches its highest value when the temperature is700℃. When the temperature is900℃, the intensity decreases and is even lower than that of as-implanted material. When the temperature is1200℃, the intensity is almost zero. Red shift happens with the increase of annealing temperature. This is related with the ratio of Ce3+/Ce4+PL spectra of samples containing1.2at%Ce annealed at1100C in different ambiences are studied. Annealing ambience has influence on the PL properties of the samples.When annealed in O2, the PL band almost disappears. Compared to annealed in air, the PL intensity increases when annealed in N2.