On the structural origin of the photoluminescence in silicon powder produced in PECVD processes
TL;DR: In this article, the origin of photoluminescence emitted by silicon powder produced by plasma-enhanced chemical vapor deposition is analyzed in view of the structural changes induced by laser annealing.
Abstract: The origin of the photoluminescence (PL) emitted by silicon powder produced by plasma-enhanced chemical vapor deposition is analyzed in view of the structural changes induced by laser annealing. Both, the Raman spectra and the PL signal are qualitatively different before and after this process. It involves some degree of recrystallization which can be deduced from the Raman spectra and also from a strong emission of H2. The analysis shows that the characteristic PL does not come from the as-grown state of the sample but from the annealed state.
Citations
More filters
TL;DR: In this paper, a model was developed that considers the particles in the powder as independent, so under vacuum the only dissipation mechanism is thermal radiation, and the supralinear dependence observed between the intensity of the emitted radiation and laser power is predicted by the model, as is the exponential quenching when the gas pressure around the sample increases.
Abstract: Previous results concerning radiative emission under laser irradiation of silicon nanopowder are reinterpreted in terms of thermal emission A model is developed that considers the particles in the powder as independent, so under vacuum the only dissipation mechanism is thermal radiation The supralinear dependence observed between the intensity of the emitted radiation and laser power is predicted by the model, as is the exponential quenching when the gas pressure around the sample increases The analysis allows us to determine the sample temperature The local heating of the sample has been assessed independently by the position of the transverse optical Raman mode Finally, it is suggested that the photoluminescence observed in porous silicon and similar materials could, in some cases, be blackbody radiation
39 citations
TL;DR: In this paper, the a−Si1−xCx:H powders were obtained from different precursor gas mixtures, from R=0.05 to R=9, where R=[SiH4]/([SiH 4]+[CH4])...
Abstract: The formation of silicon particles in rf glow discharges has attracted attention due to their effect as a contaminant during film deposition or etching. However, silicon and silicon alloy powders produced by plasma‐enhanced chemical vapor deposition (PECVD) are promising new materials for sintering ceramics, for making nanoscale filters, or for supporting catalytic surfaces. Common characteristics of these powders are their high purity and the easy control of their stoichiometry through the composition of the precursor gas mixture. Plasma parameters also influence their structure. Nanometric powders of silicon–carbon alloys exhibiting microstructural properties such as large hydrogen content and high surface/volume ratio have been produced in a PECVD reactor using mixtures of silane and methane at low pressure (<1 Torr) and low frequency square‐wave modulated rf power (13.56 MHz). The a‐Si1−xCx:H powders were obtained from different precursor gas mixtures, from R=0.05 to R=9, where R=[SiH4]/([SiH4]+[CH4])...
17 citations
01 Jan 2000
TL;DR: In this paper, the formation of particles in low-temperature, low-pressure plasmas is discussed and various technological aspects of the formation and characterization of the powders are discussed.
Abstract: Publisher Summary This chapter shows that low-pressure, low-temperature plasmas may generate a high particle nucleation rate and that they can allow for control of the composition, size, and atomic structure of the particles. These plasmas can produce nanometric particles of different composition, size, size distribution, and microstructure, depending on the discharge conditions. Besides the plasma parameters, modulation of the discharge and control of the duration of the plasma-on time can determine particle features. Results on the formation of powders of different alloys have also been presented. The scientific context of the formation of particles in low-temperature, low-pressure plasmas is reviewed. The basic studies of particles in interstellar space, the concern of the microelectronics industry about their contamination effect, the recent interest in nanostructured ceramics, and the new field of plasma crystals are also described. The various technological aspects of the formation and characterization of the powders are discussed. Detailed reports on the strong light emission observed in silicon nanoparticles produced in an rf discharge at low pressures showed that its origin is blackbody emission. In spite of using low laser intensities, nanoparticles heat up as a result of their low efficiency for dissipating heat through conduction between particles. This effect may be, in some cases, responsible for the light emission in other nanostructured materials.
11 citations
TL;DR: In this paper, the authors focus on the preparation and characterization of silicon nano-structures prepared via hydrothermal growth technology and present that there is a strong photoluminescence emission at about 400 nm and a weak one at about 700 nm.
Abstract: This very paper is focusing on the preparation and characterization of silicon nano-structures prepared via hydrothermal growth technology. The morphology and the structure given by the transmission electron microscope indicates that the silicon nanostructures are nano-crystallites, nano-wires and even nano-tubes, all of which are coated with the silica layer. Luminescence performance investigation presents that there is a strong photoluminescence emission at about 400 nm and the weak one at about 700 nm. The controllability over the thickness of the silica coating and the size of silicon nano-core were achieved via the post HF etching procedure or done by prolonging the growth period, respectively. Accordingly, the mechanism of photoluminescence emissions is discussed, which proposes that both the surface radiative recombination center be responsible for 400 nm emission, and so does the confinement effect of the optical phonon for 700 nm. It might, also, come to that the Si H x bonds on the surface of the exorbitantly HF etched SiNS samples probably gives rise to the 390 nm emission.
3 citations
References
More filters
TL;DR: In this paper, free standing Si quantum wires can be fabricated without the use of epitaxial deposition or lithography using electrochemical and chemical dissolution steps to define networks of isolated wires out of bulk wafers.
Abstract: Indirect evidence is presented that free‐standing Si quantum wires can be fabricated without the use of epitaxial deposition or lithography. The novel approach uses electrochemical and chemical dissolution steps to define networks of isolated wires out of bulk wafers. Mesoporous Si layers of high porosity exhibit visible (red) photoluminescence at room temperature, observable with the naked eye under <1 mW unfocused (<0.1 W cm−2) green or blue laser line excitation. This is attributed to dramatic two‐dimensional quantum size effects which can produce emission far above the band gap of bulk crystalline Si.
7,393 citations
IBM1
TL;DR: In this article, the number and nature of the silicon-hydrogen bonds in amorphous silicon films prepared in plasmas either of silane or of hydrogen and argon were studied.
Abstract: We have studied the number and nature of the silicon-hydrogen bonds in amorphous silicon films prepared in plasmas either of silane or of hydrogen and argon. The films from silane glow discharges have qualitatively different Raman and infrared spectra which depend on deposition parameters such as substrate temperature and silane gas pressure. Three main groups of spectral bands are seen associated with the Si-H bonds: the Si-H bond stretch bands, the bands due to relative bending of two or three Si-H bonds with a common silicon atom, and the "wagging" bands of Si-H bonds with respect to the Si matrix. These bands are split in a way suggestive of the presence of SiH, Si${\mathrm{H}}_{2}$, and Si${\mathrm{H}}_{3}$ complexes: the bond-bending bands are absent when only SiH bonds are present. All three types of complexes are identified in films deposited from glow discharges of silane at pressures \ensuremath{\sim} 1 Torr and room temperature. Higher substrate temperatures and/or lower pressures reduce the Si${\mathrm{H}}_{2}$ and Si${\mathrm{H}}_{3}$ concentrations: films deposited at 250\ifmmode^\circ\else\textdegree\fi{}C and 0.1 Torr contain only SiH groups. From the strength of the corresponding absorption bands, H concentrations as high as 35 to 52 atomic percent are estimated. Films sputtered at 200\ifmmode^\circ\else\textdegree\fi{}C in a 10% ${\mathrm{H}}_{2}$-90% Ar mixture contain all three groupings observed in the silane-derived samples. Deuterated sputtered films are used to confirm the analysis. The first- and second-order Raman scattering spectra of the Si-Si bonds in pure and hydrogenated $a\ensuremath{-}\mathrm{S}\mathrm{i}$ are also discussed. The scattering efficiency of $a\ensuremath{-}\mathrm{S}\mathrm{i}$ is found to be as much as 10 times that of crystal Si. The depolarization ratio of the $a\ensuremath{-}\mathrm{S}\mathrm{i}$ Raman spectrum has been remeasured. Finally, a picture is presented of when it is appropriate to refer to heavily hydrogenated $a\ensuremath{-}\mathrm{S}\mathrm{i}$ as still being a material describable by $a\ensuremath{-}\mathrm{S}\mathrm{i}$ network models.
1,405 citations
TL;DR: In this paper, the authors compared the luminescence and vibrational properties of anodically oxidized (porous) silicon and of chemically synthesized siloxene (Si 6 O 3 H 6 ) and its derivates.
Abstract: Luminescence and vibrational properties (infrared and Raman) of anodically oxidized (“porous”) silicon and of chemically synthesized siloxene (Si 6 O 3 H 6 ) and its derivates are compared. Based on the quantitative agreement of these two types of materials it is concluded that the origin of the strong room temperature luminescence in “porous” silicon can be traced to siloxene derivates present in “porous” silicon.
738 citations
TL;DR: In this paper, the energy and polarization characteristics of the one and two-phonon Raman spectrum have been measured using a 180\ifmmode^\circ\else\text degree\fi{} backscattering technique.
Abstract: The energy and polarization characteristics of the one- and two-phonon Raman spectrum have been measured using a 180\ifmmode^\circ\else\textdegree\fi{} backscattering technique. The two-phonon spectrum was measured at 20, 80, and 305\ifmmode^\circ\else\textdegree\fi{}K. The one-phonon spectrum was measured at 17, 30, 80, and 305 \ifmmode^\circ\else\textdegree\fi{}K. The one-phonon line of symmetry ${\ensuremath{\Gamma}}_{25}$, was shown to be Lorentzian and to have a deconvoluted half-width at 17 \ifmmode^\circ\else\textdegree\fi{}K of 1.45 \ifmmode\pm\else\textpm\fi{} 0.05 ${\mathrm{cm}}^{\ensuremath{-}1}$. The two-phonon Raman spectrum was used to determine phonon energies at the four critical points $\ensuremath{\Gamma}$, $X$, $L$, and $W$.
581 citations
TL;DR: The structural analysis showed that the materials consist of small crystalline silicon particles surrounded by hydrogen atoms, whose diameters are 20--30 A\r{}.
Abstract: We have succeeded in fabricating the mostly crystallized Si:H materials having a wide optical band gap of up to 2.4 eV by means of a reactive sputtering technique with a low substrate temperature of \ensuremath{\sim}100 K. The structural analysis showed that the materials consist of small crystalline silicon particles surrounded by hydrogen atoms, whose diameters are 20--30 A\r{}. The widening of the optical band gap can be explained by a three-dimensional quantum-well effect in the small particles.
400 citations