In situ Fourier transform infrared absorption spectroscopy has been used to study the composition of particles formed and suspended in radio-frequency discharges of silane-oxygen-argon gas mixtures. The silane gas consumption was observed by infrared absorption. The stoichiometry of the produced particles depends on the silane flow rate and was compared with commercial colloidal silica. A small proportion of silane gas produces nanometric stoichiometric particles whereas a large proportion produces larger under-stoichiometric particles. Absorption spectroscopy was sufficiently sensitive to reveal particles too small to be visually observed by laser light scattering. Post-oxidation of hydrogenated silicon particles trapped in an argon plasma was obtained by adding oxygen. Mass spectrometry of negative and positive ions showed an extensive range of ionic clusters which may be at the origin of the observed particle formation. A model based on an iterative reaction sequence gives a good agreement with the measured positive ion mass spectrum.

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Silicon oxide particle formation in RF plasmas investigated by infrared absorption spectroscopy and mass spectrometry

Silicon rich oxide (SRO) films with different silicon excess were deposited by low pressure chemical vapor deposition (LPCVD) using SiH 4 and N 2 O as the reactant gasses. A set of SRO films was implanted with silicon ions (SI-SRO). After thermal annealing, SRO and SI-SRO films with low Si excess showed a strong visible photoluminescence (PL) in the 1.4–2.1 eV range, characteristic of silicon nanocrystals (Si-nc's) formation. For SRO layers, a redshift of the PL peak was only observed by increasing the silicon excess from 4 to 5.1 at. %, no redshift took place when the silicon excess was 12.7 at. %. The SI-SRO films exhibited a similar behaviour. For implanted and non implanted samples, transmission electron microscopy analysis only showed silicon clusters when the silicon excess was higher than 5 at. %. It has been observed that the Si-clusters size was larger as the silicon excess increased and that the Si-clusters density increased when the SRO films were implanted. Therefore, a stronger PL response was observed in the SI-SRO films. The structural and optical properties of SRO and SI-SRO films have been related, suggesting that the emission could be associated to Si-clusters/defects interaction.

Optical characterization of silicon rich oxide films

It is well known that silicon-rich oxide (SRO) shows intense photoluminescence (PL). In this work, the authors studied the relationship of the surface morphology and the PL emission. PL spectra of SRO as a function of the excess silicon, temperature, and time of thermal annealing were obtained. The same samples were studied using transmission electronic microscopy and atomic force microscopy to determine their microstructure and surface morphology. A relationship between silicon agglomerates in the SRO and the surface morphology was obtained. Then, the red PL emission was related to the surface morphology. The authors found that the surface roughness is an important parameter for the high red emission of SRO.

Analysis of surface roughness and its relationship with photoluminescence properties of silicon-rich oxide films

In order to have optoelectronic functions integrated in a single chip, it is very important to obtain a silicon compatible material with an optimal photoluminescence response. The non-stoichiometric silicon oxide (SiOx) has shown photoluminescence response and is also compatible with silicon technology. In this work, the composition and optical properties of the SiOx films are studied using null ellipsometry, Fourier transformed infrared spectroscopy (FTIR), atomic force microscopy (AFM), and photoluminescence (PL). The SiOx films were growth to different temperatures. The IR absorption spectrum shows the presence of three typical Si–O–Si vibrations modes in SiO2. However, changes in their intensity and position were observed. Also, when growth temperature decreased, the Si–H vibrations modes were observed. These changes are directly related with compositional variation in the SiOx films due to the growth temperature. A PL spectrum shows a considerable emission in the range 400–850 nm that varies with the growth temperatures.

FTIR, AFM and PL properties of thin SiOx films deposited by HFCVD

Motivated by the necessity to have all silicon optoelectronic circuits, researchers around the world are working with light emitting silicon materials. Such materials are silicon dielectric compounds with silicon content altered, such as silicon oxide or nitride, enriched in different ways with Silicon. Silicon Rich Oxide or silicon dioxide enriched with silicon, and silicon rich nitride are without a doubt the most promising materials to reach this goal. Even though they are subjected to countless studies, the light emission phenomenon has not been completely clarified. So, a review of different proposals presented to understand the light emission phenomenon including emissions related to nanocrystals and to point defects in SiO2 is presented.

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Emission mechanisms of Si nanocrystals and defects in SiO 2 materials

A comparative study of compositional and optical properties of silicon-rich oxide (SRO) films deposited by low-pressure chemical vapor deposition (LPCVD) and plasma-enhanced chemical vapor deposition (PECVD) is presented. Infrared spectra revealed the presence of hydrogen bonded to silicon atoms in the SRO–PECVD films, whereas in SRO–LPCVD films the IR spectra looked like the stoichiometric thermal silicon oxide. Moreover, X-ray photoelectron spectroscopy (XPS) studies showed that the SRO–PECVD films contain a higher content of nitrogen than SRO–LPCVD films. In spite of differences, the SRO films obtained by both methods show a strong room-temperature photoluminescence (PL). However, the highest PL intensity was emitted by SRO films obtained by LPCVD.

Comparative study between silicon-rich oxide films obtained by LPCVD and PECVD

Optical properties of non-stoichiometric SiO2 as a function of excess silicon content and thermal treatments

The electrical properties of silicon-rich oxide (SRO) films in metal–oxide–semiconductor-like structures were analysed by current versus voltage (I–V) and capacitance versus voltage (C–V) techniques. SRO films were thermally annealed to activate the agglomeration of the silicon excess in the form of nanoparticles (Si-nps). High current was observed at low negative and positive voltages, and then at a certain voltage (Vdrop), the current dropped to a low conduction state until a high electric field again activated a high conduction state. C–V measurements demonstrated a capacitance reduction at the same time as the current dropped, but without appreciable flat-band voltage (VFB) shifting. The reduction in capacitance and current was also observed after applying an electrical stress. These effects are ascribed to the annihilation of conductive paths created by Si-nps. An equivalent circuit is used to explain the capacitance and current reductions. Finally, the conduction mechanism is also analysed by making use of trap assisted tunnelling and Fowler–Nordheim tunnelling at low and high electric fields, respectively.

http://iopscience.iop.org/article/10.1088/0957-4484/20/4/045201/pdf

The mechanism of electrical annihilation of conductive paths and charge trapping in silicon-rich oxides

Charge trapping effect in silicon-rich oxide (SRO) films was investigated using capacitance versus voltage (C–V), current versus voltage (I–V) and current versus time (I–t) measurements in an Al/SRO/Si MOS-like structure. SRO layers with different thicknesses were deposited. The trapped charge density was found to depend on the thickness of the SRO layers. It was shown that the total trapped charges can be divided into two parts: one part is correlated with the Si nanoclusters located near the SRO/Si interface (interface-NCs); another one is correlated with the Si nanoclusters distributed in the bulk of the SRO layers (bulk-NC). A current peak was observed in the I–V curves in the surface inversion condition. The peak position voltage varies with the thickness of the SRO layers. The current peak is attributed to the charging/discharging of the interface-NCs. The charging/discharging process of interface-NCs was evidenced by a fast decay of current in I–t measurements at the current peak voltage. I–t curves recorded at a large positive voltage are associated with the charge trapping effect of the bulk-NCs. The Coulomb blockade effect was suggested to be the reason of current decay at constant voltage.

http://iopscience.iop.org/article/10.1088/0957-4484/14/9/304/pdf

M. Aceves

Papers

Comparative study between silicon-rich oxide films obtained by LPCVD and PECVD

Optical properties of non-stoichiometric SiO2 as a function of excess silicon content and thermal treatments

The mechanism of electrical annihilation of conductive paths and charge trapping in silicon-rich oxides

Single electron charging in Si nanocrystals embedded in silicon-rich oxide

Duality metal oxide semiconductor–PN junction in the Al/silicon rich oxide/Si structure as a radiation sensor