Evolution with the annealing treatments of the photoluminescence mechanisms in a-SiNx:H alloys prepared by reactive evaporation

Abstract

A wide range of amorphous hydrogenated silicon nitride thin films with an excess of silicon was prepared by evaporation of silicon under a flow of nitrogen and hydrogen ions. A strong visible photoluminescence at room temperature was observed for the as-deposited films as well as for films annealed up to 1100°C. The chemical composition and the structure of the films were investigated using x-ray photoelectron, thermal desorption, and Raman spectroscopies, infrared absorption measurements, grazing incidence x-ray diffraction experiments, and transmission electron microscopy. Two luminescence mechanisms were identified for the films depending on the annealing temperature. For annealing temperatures below 650°C, the films are made of amorphous silicon-rich phases mixed with nitrogen-rich phases. These inhomogeneities in the chemical composition, coupled with the evolution of the photoluminescence energies and intensities with the hydrogen content, suggest that the emission is due to the recombination process of the photogenerated carriers within the band-tail states. For temperatures higher than 800°C, a phase separation occurs and the films could be described as silicon nanoclusters embedded in an insulating amorphous silicon nitride matrix. The clusters are amorphous, and then crystallized when the annealing temperature is high enough. The correlation between the clusters sizes and the photoluminescence results suggests that the emission observed after annealing treatments at temperature higher than 900°C is due to the quantum confinement of the carriers inside the silicon clusters. By carefully choosing the preparation and the annealing conditions, it is possible to tune the photoluminescence energy in the visible range.

Annealing effects on aSiNx grown by PECVD using different gas mixtures

“…This interpretation is consistent with the results of Ref. [8] on evaporated SiN x , where absence of hydrogen in the films above 800°C is reported. A sudden increase is afterwards found following the final annealing step (1100 °C).…”

“…1 can be explained in terms of the quantum confinement model, as caused by a thermally induced nanoparticle enlargement. On the other hand, as already mentioned, the PL emission in silicon nitride has been also ascribed to radiative recombination of carriers that thermalize in the conduction and valence band tails (band tail states model) [6,8]. In this case the PL peak shift with systematic changes in material stoichiometry is determined by the enlargement of the bandgap when the concentration of alloying N atoms is raised.…”

“…A mixture of a silicon-rich phase and a phase containing more nitrogen, as proposed in ref. 8 could be a possibility. With such microstructure, some carrier confinement in the lower gap regions can be expected, and, with appropriate dimensions for the Si-rich aggregates, the quantum confinement effect could explain the luminescence.…”

The effects of annealing temperature on photoluminescence of silicon nanoparticles embedded in SiNx matrix

“…In comparison with silicon nanoparticles embedded in silicon oxide matrix, the silicon nanoparticles embedded in silicon nitride matrix show relatively lower barrier for carriers and more intense light emission [2,6]. Another major interest for using silicon nitride systems rather than silicon oxide systems is the possibility to get efficient light emission at shorter wavelength region [2,7]. Thus, silicon nitride thin films with silicon nanoparticles have the potential to produce full color emission devices.…”

The effects of annealing temperature on the photoluminescence from silicon nitride multilayer structures

“…Silicon nanocrystals embedded in silicon nitride [1][2][3][4][5][6][7][8] have received attention as promising materials for optoelectronic applications. Spectroscopic photoluminescence (PL) is an extensively used tool to explore quantum confinement effects from nanostructures.…”