Green Emission of Terbium Doped Silicon Rich Silicon Oxide Films Obtained By Chemical Vapor Deposition

The effect of silicon concentration, annealing temperature and influence of post-growth hydrogen incorporation on terbium (Tb³⁺) luminescence was investigated for thin silicon rich silicon oxide films (SRSO). The structures were deposited by means of plasma enhanced chemical vapor deposition (ECR-PECVD). The structural properties of these films were investigated by Rutherford backscattering spectrometry, transmission electron microscopy, FTIR and Raman scattering. The optical properties were investigated by means of photoluminescence, cathodoluminescence and photoluminescence decay spectroscopy.

In this poster, we present a detailed discussion of these issues and determine the optimal conditions of the SRSO films from the point of view of Tb³⁺ emission properties.

An increase in the Si concentration in SRSO influences the emission properties in two ways. First of all, the refractive index of the film increases which enhances the oscillator strength of the optical transitions. On the other hand, the non-radiative recombination also increases, limiting the PL intensity. Therefore, from the point of view of emission efficiency, the optimal Si concentration in the film is about 35 at.% Si. Besides the Si concentration, another effect investigated in this work was the influence of the annealing temperature on Tb³⁺ emission. It was found that the PL intensity increases as a function of the annealing temperature. This effect was ascribed to the structural changes of the SRSO matrix. At early stages of the annealing (up to annealing temperature equal to 900^oC) the most important factor enhancing the Tb³ emission intensity is a reduction in the number of non-radiative recombination centers. However, as shown by Raman measurements, starting from Ta =1100^oC structural changes occur in the matrix (crystallization and formation of the Si nanocrystals) and the Tb environment significantly changes. Therefore, the further increase in the PL intensity obtained for high annealing temperatures (temperatures in the 1100–1200 ^oC range) can be ascribed to the increasing oscillator strength of the intra-4f transitions, induced by the change of the crystal field around the ions.