G. Zatryb

Effects of Si-rich oxide layer stoichiometry on the structural and optical properties of Si QD/SiO2 multilayer films

The effects of the stoichiometry of the Si-rich oxide (SRO) layer, O/Si ratio, on the structural and optical properties of SRO/SiO2 multilayer films were investigated in this work. SRO/SiO2 multilayer films with different O/Si ratios were grown by a co-sputtering technique, and Si quantum dots (QDs) were formed with post-deposition annealing. By transmission electron microscopy (TEM) and glancing incidence x-ray diffraction (GIXRD), it was found that the Si QD size decreases with increases in O/Si ratio. The photoluminescence (PL) spectrum varies with the O/Si ratio in band position, shape and intensity. In addition, it was observed that the absorption edge blue-shifts with increases in the O/Si ratio. The change in the absorption edge is consistent with strengthening quantum confinement effects in Si QDs, as indicated by TEM and GIXRD. The optical properties were also investigated by 2D photoluminescence excitation (2D-PLE) and lifetime measurements. The origin of emission and absorption is discussed based on the absorption, PL, 2D-PLE and decay time measurements.

On the nature of the stretched exponential photoluminescence decay for silicon nanocrystals

The influence of hydrogen rate on optical properties of silicon nanocrystals deposited by sputtering method was studied by means of time-resolved photoluminescence spectroscopy as well as transmission and reflection measurements. It was found that photoluminescence decay is strongly non-single exponential and can be described by the stretched exponential function. It was also shown that effective decay rate probability density function may be recovered by means of Stehfest algorithm. Moreover, it was proposed that the observed broadening of obtained decay rate distributions reflects the disorder in the samples.

Effect of annealing and Nd concentration on the photoluminescence of Nd3+ ions coupled with silicon nanoparticles

We report on the microstructure and photoluminescence(PL) properties of Nd-doped SiO2 thin films containing silicon nanoparticles (Si-np) as a function of the annealing temperature and the Nd concentration. The thin films, which were grown on Si substrates by reactive magnetron co-sputtering, contain the same Si excess. Fourier transform infrared (FTIR)spectra show that a phase separation occurs during the annealing due to the agglomeration of the Si excess resulting in the formation of Si-np. Besides, after annealing, the films exhibit PL from excitonic states confined in Si-np. We showed that the intensity of the PL of Nd3+ions that occurs at ∼0.92, 1.06, and 1.4 μm is maximal at low Nd concentration and while well-passivated Si-np are formed. FTIR and x-ray measurements showed that the increase in the Nd incorporation has detrimental effects on the PL of Nd3+ because of the formation of Nd2O3nanocrystals and inherent disorder in the SiO2 host matrix. PL excitation measurements demonstrate that the PL of Nd3+ions is nonresonant and follows the excitation of Si-np giving new evidence of the energy transfer from Si-np toward the rare earth ions.

Correlation between stress and carrier nonradiative recombination for silicon nanocrystals in an oxide matrix

Silicon nanocrystals embedded in an oxide matrix formed in a multilayer architecture were deposited by the magnetron sputtering method. By means of Raman spectroscopy we have found that compressive stress is exerted on the silicon nanocrystal core. The stress varies as a function of silicon concentration (O/Si ratio) in the silicon-rich oxide (SRO) layers, which can be attributed to the changing nanocrystal environment. By conducting the time-resolved spectroscopy experiment, we demonstrate that, depending on the nanocrystal surroundings, a different amount of nonradiative recombination sites participates in the excited carrier relaxation process, leading to changes of the relative quantum yield of photoluminescence.

Influence of the annealing temperature and silicon concentration on the absorption and emission properties of Si nanocrystals

Silicon nanocrystals embedded in a silicon-rich silicon-oxide matrix have been fabricated at different silicon contents (38%, 40%, and 49%) using plasma-enhanced chemical vapor deposition and annealing at different temperatures in the range from 900 °C to 1100 °C. Their optical properties have been investigated by photoluminescence and transmittance measurements. Strong, room-temperature emission bands at ∼1.6 eV have been observed for all samples, with intensities dependent on the annealing temperature and Si content of the samples. From transmittance measurements, a redshift of the absorption edge has been detected when increasing the annealing temperature or Si content.

Green light emission from terbium doped silicon rich silicon oxide films obtained by plasma enhanced chemical vapor deposition

The effect of silicon concentration and annealing temperature on terbium luminescence was investigated for thin silicon rich silicon oxide films. The structures were deposited by means of plasma enhanced chemical vapor deposition. The structural properties of these films were investigated by Rutherford backscattering spectrometry, transmission electron microscopy and Raman scattering. The optical properties were investigated by means of photoluminescence and photoluminescence decay spectroscopy. It was found that both the silicon concentration in the film and the annealing temperature have a strong impact on the terbium emission intensity. In this paper, we present a detailed discussion of these issues and determine the optimal silicon concentration and annealing temperature.

Correlation between matrix structural order and compressive stress exerted on silicon nanocrystals embedded in silicon-rich silicon oxide

AbstractSilicon nanocrystals embedded in a silicon oxide matrix were deposited by radio frequency reactive magnetron sputtering. By means of Raman spectroscopy, we have found that a compressive stress is exerted on the silicon nanocrystal cores. The stress varies as a function of silicon concentration in the silicon-rich silicon oxide layers varies, which can be attributed to changes of nanocrystal environment. By conducting the Fourier transform infrared absorption experiments, we have correlated the stresses exerted on the nanocrystal core to the degree of matrix structural order.PACS78.67.Bf, 78.67.Pt, 73.63.Bd, 78.47.D, 74.25.Nd

On the origin of emission and thermal quenching of SRSO:Er3+ films grown by ECR-PECVD.

Silicon nanocrystals embedded in a silicon-rich silicon oxide matrix doped with Er3+ ions have been fabricated by electron cyclotron resonance plasma-enhanced chemical vapor deposition. Indirect excitation of erbium photoluminescence via silicon nanocrystals has been investigated. Temperature quenching of the photoluminescence originating from the silicon nanocrystals and the erbium ions has been observed. Activation energies of the thermally activated quenching process were estimated for different excitation wavelengths. The temperature quenching mechanism of the emission is discussed. Also, the origin of visible emission and kinetic properties of Er-related emission have been discussed in details.

Ion?ion interaction in two-dimensional nanoporous alumina filled with cubic YAlO3?:?Tb3+ matrix

Terbium doped YAlO3 composites, with terbium concentrations up to 2.11 at%, were fabricated by co-precipitation in porous anodic alumina films grown on silicon. The presence of the cubic YAlO3 phase was confirmed by x-ray diffraction and FT-IR analysis. The fabricated samples demonstrate photoluminescence (PL) within the range 350?640?nm, which is associated with f?f transitions from the 5D3, 5G6 and 5D4 levels of Tb3+ ion. Additionally, a broad and fast- decaying PL band in the blue range has been observed, which is associated with defect states. Based on PL excitation spectra, the main excitation channel of Tb3+ ions is due to 4f?5d transitions. Excitation bands observed at 235, 270 and 320?nm have been related to the permitted low-spin 5d2 [LS], 5d1 [LS] and forbidden high-spin 5d1 [HS] states, respectively. The PL decay spectra have been measured, with the results analysed using the maximum entropy method; a strong indication of ion?ion interaction has been observed. The distribution of Tb3+ ions in the PAA?:?YAlO3 structure has been proposed and its influence on optical properties of Tb3+ ions has been discussed.

Influence of Europium Concentration on Optical and Structural Properties of Nanocrystalline GaN : Eu3 + Powder

In this work, GaN nanocrystals doped by europium (III) ions at different concentrations have been synthesized by modified nitridation method at 1050°C temperature. From X-ray diffraction spectra, it has been found that the size of nanocrystals strongly depends on the dopant concentration in a nonlinear way and varying from ∼ 20 up to 35 nm when the europium concentration varies from 0.5 up to 2 mol %. Moreover, it has been found that obtained nanocrystals are characterized by two main emission bands, one related to GaN core (∼ 364 nm) and the second to surface/defect states (∼ 600 nm). It has been shown that the relative intensity of these bands varies with changing of the europium concentration due to changes of GaN nanocrystals surface-to-volume ratio.