Optical Properties Of Europiom-doped Silicon Rich Oxide Thin Films

Light emitter is one of most important issues silicon-based photonics now facing. Because of the indirect band gap of silicon, making it be not suitable for optical active devices. However, rare-earth (RE) ions have attracted great interest all over the world for its high luminescence intensity, monochromatic and stable performance at room temperature. Therefore, RE-doped silicon based light emitting materials and devices may be the choice of light source of silicon photonics. In this work, photoluminescence (PL) and electroluminescence (EL) performance of Europium (Eu)-doped silicon rich oxide (SRO) thin films have been investigated, to expore its ways as the light emitterof silicon photonics.Eu-doped SRO films have been prepared by electron beam evaporation (EBE). The dose of Eu was controlled by controlling the dose in the evaporation source. The influence of sample preparation and followed heat treatment on the PL performance is studied in detail. While the main results are summarized as follow:1) Dense and uniform Eu-doped SRO films can be prepared by the method of EBE. We found PL intensity was dependent on temperature of substrate during deposition process. On the other hand, the PL of as-deposited sample can be increased by post-annealing.2) A reduction process of Eu³⁺ has been taken place during the film deposition. Eu³⁺ in the evaporation source was reduced to Eu²⁺ in the film during deposition, while SiO get O from Eu₂O₃ to form SiO₂.3) The luminescence and structure evolution of Eu-doped SRO films were investigated after post-annealing. PL shows significant intensity enhancement after 1100℃annealing. This enhancement is associated with the formation of europium silicate (EuSiO₃), which is confirmed by x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD) and transmission electron microscopy (TEM) results. During annealing, the luminescence mechanism transfers from light emitting of defect related state in SRO film to an energy level transition between 4f⁶5d and 4f⁷(⁸S_7/2) of Eu³⁺.4) Eu-doped SRO films have been used to produce the ITO/Eu_xSi_yO_z/p-Si/AI MOS device structures to realize its EL. The MOS devices emitted visible light originated from radiative recombination of defect related state in SRO film. However, the EuSiO₃ particles formed during high temperature annealing provided a channel for carries and resulted in a large injection current. After improving the device structure, more intense EL from the 4f⁶5d-4f⁷ energy levels of Eu²⁺ was emitted from device with a lower injected current.