Effect of acetone vapor treatment on photoluminescence of porous nc-Si–SiOx nanostructures

The effect of treatment in saturated acetone vapors on the spectral composition and intensity of photoluminescence (PL) in porous oblique deposited SiOx films is studied. As a result of this treatment followed by high-temperature annealing at the temperature 930 °C, considerable PL intensity growth and the small blueshift of PL peak position are observed in the porous, column-like structure films containing Si nanocrystals. A more intense shortwave band (peak position – 540-560 nm) appears in the PL spectrum of these structures, in addition to the longwave band (760-780 nm). Both PL bands in treated samples are characterized by monomolecular radiative recombination, which can be attributed to annihilation of excitons in silicon nanocrystals embedded into oxide matrix (longwave band) and in carbon-enriched matrix near surface of oxide nanocolumns (shortwave band). The possibility to control the PL characteristics of the porous structures in a wide spectral range by above treatment is shown

Absorption Cross Section and Photoluminescence Lifetime of Silicon-Based Light-Emitting nc-Si-SiOx Structures

The spectral dependence of the photoluminescence (PL) decay kinetics at room temperature have been studied in porous nc-Si-SiOx nanostructures. Investigated samples were obtained by oblique evaporation of SiO with following annealing at 975 C in vacuum and treating in the HF vapor at 50 C. PL decay in these structures described by a stretched exponential and the average lifetime of the PL decrease exponentially with increasing energy of photons. PL lifetime values is in microsecond range that point out on phonon participation in radiative recombination. Dispersion parameter do not depend on emission energy and tends to 1 with increasing porosity, which is consistent with the model of noninteracting nc-Si. It was established, that the absorption cross section σ of the nc-Si particles increase with decreasing of nc-Si dimensions and increasing of emission energy. This result is consistent with the quantum confinement effects, where the smaller nc-Si with larger energy gaps are characterized by a short radiative lifetime and the corresponding radiative recombination process take place within the individual nc-Si. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3501

Nickel-induced enhancement of photoluminescence in nc-Si–SiOx nanostructures

The effect of nickel silicide interlayer on the intensity of photoluminescence (PL) from Si nanoclusters (nc) in normally deposited and obliquely deposited in vacuum SiOx/Ni/Si structures have been studied using spectral and time-resolved PL measurements. It has been shown that the intensity of PL band in SiOx/Ni/Si samples is essentially higher than that in reference SiOx/Si samples (without the nickel interlayer) with the same characteristics and treatment. The PL intensity enhancement factor is equal to 5.77 for normally deposited samples and 18 for obliquely deposited samples. The unchanged spectral shape of PL bands and similar position of PL maximum in samples with and without nickel silicide interlayer indicates that in the SiOx/Ni/Si structures after annealing no additional emitting centers are introduced to compare with reference one. Time-resolved measurements showed that PL decay rate was decreased from 8.2*10⁴ s⁻¹ for SiOx/Si specimens to 2.86*10⁴ s⁻¹ for SiOx/Ni/Si one. The emission decay rate distribution was determined by fitting the experimental decay curves to the stretchedexponential model. The observed narrow decay rate distribution, decrease of the PL decay rate and enhancement of the PL intensity in SiOx/Ni/Si samples can be assigned to the processes of nickel silicide passivation of the dangling bonds at the interface of Si nanoparticles and the silicon oxide matrix, which is more effective in porous samples

Polarization memory of photoluminescence related with Si nanoparticles embedded into oxide matrix

Investigated in this paper have been polarization properties of photoluminescence in solid and porous nc-Si−SiOx light emitting structures passivated in HF vapor. These structures were produced by thermal vacuum evaporation of silicon monoxide SiO powder onto polished c-Si substrates. After annealing in vacuum for 15 min at the temperature 975 °C, SiOx films were decomposed to SiO₂ with Si nanoclusters embedded in the oxide matrix. Comparison of polarizations, inherent to exciting light and that of film photoluminescence, enabled to find the polarization memory effect in the passivated structures. In anisotropic porous nc-Si−SiOx samples, obtained by oblique deposition in vacuum, there is also well-defined orientation dependence of the PL polarization degree in the sample plane. This dependence is related to the orientation of oxide nanocolumns that form the structure of the porous layer. The above effects are associated with transformation during etching in HF the symmetric Si nanoparticles to asymmetric elongated ones

Polarization conversion effect in obliquely deposited SiOx films

Structural anisotropy of the SiOx films and nc-Si-SiOx light emitting nanostructures, prepared by oblique deposition of silicon monoxide in vacuum, has been studied using the polarization conversion (PC) effect. For this purpose, a simple method of PC investigation with usage of a standard null-ellipsometer is proposed and tested. This method is based on the analysis of the azimuthal angle dependence of the offdiagonal elements of the Jones matrix. The electron microscopy study shows that obliquely deposited SiOx films have a porous (column-like) structure with the column diameter and inclination depending on the deposition angle. Polarimetric investigations revealed that both in-plane and out-of-plane anisotropy was present, which is associated with the columnar growth. The correlation between the PC manifestations and the scanning electron microscopy results is analyzed. It was found that the tilt angle of columns in obliquely deposited SiOx is smaller than that predicted by the “tangent rule” and “cosine rule” models, and depends on the crystallographic orientation of Si substrate. It is concluded that the proposed method is effective non-destructive express technique for the structural characterization of obliquely deposited films

Controlling the photoluminescence spectra of porous nc-Si–SiOx structures by vapor treatment

The effect of HF and H₂O₂ vapor treatment on the spectral composition and intensity of photoluminescence (PL) in porous oblique deposited nc-Si–SiOx structures have been studied using FTIR, electron-spin resonance (EPR) and PL measurements. As a result of HF vapor treatment, considerable PL intensity growth and blueshift of PL peak position are observed. It is suggested that the evolution of the PL spectra in HF vapor-treated samples can be attributed to selective-etching-induced decrease in Si nanoparticle dimensions and to passivation of Si dangling bonds (that are nonradiative recombination trap states) by hydrogen and oxygen. Additional treatment in H₂O₂ vapor results in additional nc-Si surface oxidation and reduction of nc-Si size. The possibility to control the PL characteristics (peak position and intensity) of the porous nc-Si–SiOx structures in a wide range by above treatments is shown