Amorphous silicon oxide thin films were prepared by the coevaporation technique in ultrahigh vacuum. Different compositions were obtained by changing the evaporation rate of silicon. The samples were then annealed to different temperatures up to 950°C. The composition and the structure were investigated using energy dispersive x-ray spectroscopy, infrared absorption measurements, and Raman spectroscopy. This study attests the presence of amorphous silicon clusters in a silicon oxide matrix. Optical transmission measurements were performed and interpreted in the field of the composite medium theory. The obtained results are in good agreement with the presented structural model. The photoluminescence in the red-orange domain was studied in relation with the structure. The correlation between the photoluminescence energy and intensity and the structure shows that the light emission originates from the silicon clusters embedded in the silicon oxide matrix. Moreover the dependence of the photoluminescence energy with the silicon volume fraction suggests the origin of the light emission could be due to a quantum confinement effect of carriers in the amorphous silicon clusters.

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.

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Amorphous GeO x alloys were prepared by evaporation of GeO 2 powder on substrates maintained at 100°C. The evolution of the structure was investigated by infrared-absorption spectrometry, Raman spectrometry and transmission electron microscopy experiments for annealing temperatures less than 600°C. These experiments allowed us to follow the phase separation of the alloy and to observe the appearance of amorphous and crystallized Ge aggregates. The evolution of the photoluminescence in the range of 560-1550 nm was correlated to the structure of the films.

This study attempts to clarify the origin of the temperature dependence of the photoluminescence ͑PL͒ spectra of silicon nanocrystals ͑Si-ncs͒ embedded in SiO 2 from 5 to 300 K. For this purpose, size-controlled Si-ncs with a narrow size distribution were fabricated, using the SiO/ SiO 2 multilayer structure. The PL intensity is strongly temperature dependent and presents a maximum at around 70 K, depending on the Si-nc size and on the excitation power. The origin of this maximum is first discussed thanks to PL dynamics study and power dependence study. The evolution of the PL energy with temperature is also discussed. In bulk semiconductors the temperature dependence of the gap is generally well represented by Varshni's law. Taking into account the quantum confinement energy, the PL energy of Si-ncs follows very well this law in the range 50-300 K. Below 50 K, a strong discrepancy to this law is observed characterized by a strong increase in the PL energy at low temperature, which is dependent on the Si-nc size distribution. This temperature dependence of the PL energy is correlated with a decrease in the radiative rate at low temperature and is explained by a preferential saturation effect of the bigger Si-ncs.