The blue cathodoluminescence and photoluminescence of porous silicon nanoribbons

The porous silicon nanoribbons were fabricated via two steps: first, the silicon nanoribbons were obtained using a high temperature oxide assisted method; and then they were etched by HF solution to form nanoporous cavities. These porous silicon nanoribbons exhibited stable blue cathodoluminescence and photoluminescence, which might be related to the quantum size effect.     

Raman scattering and photoluminescence study of porous silicon formed on n-type silicon

We report Raman scattering and photoluminescence studies on porous silicon film formed on n-type silicon. The Raman spectra over the sample surface exhibit considerable variation whereas the photoluminescence spectra are practically identical. Our results indicate that, well inside the film surface, it consists of spherical nanocrystals of typical diameter ≈ 100Å, while on the edge these nanocrystals are ? 300Å. We further observe that there is no correlation between the photoluminescence peak position and the nanocrystal diameter. This suggests that the origin of the photoluminescence is due to radiative recombination between defect states in the bulk as well as on the surface of the nanocrystal.     

On the origin of photoluminescence in silicon nanocrystals: pressure-dependent structural and optical studies

A lack of consensus persists regarding the origin of photoluminescence in silicon nanocrystals. Here we report pressure-dependences of X-ray diffraction and photoluminescence from alkane-terminated colloidal particles. We determine the diamond-phase bulk modulus, observe multiple phase transitions, and importantly find a systematic photoluminescence red shift that matches the X(conduction)-to-Γ(valence) transition of bulk crystalline silicon. These results, reinforced by calculations, suggest that the efficient photoluminescence, frequently attributed to defects, arises instead from core-states that remain highly indirect despite quantum confinement.     

Effect of natural aging on photoluminescence of porous silicon

The influence of natural aging on the intensity and position of the photoluminescence (PL) peak in n-type porous silicon (por-Si) has been studied. Changes in the phase composition and relative content of the amorphous and oxide phases in por-Si during aging were determined by simulating the spectra of Si L _2,3 ultrasoft X-ray emission based on the reference spectra of the corresponding phases.     

The interface mechanism of photoluminescence in carbonized porous silicon

The interface mechanism of photoluminescence (PL) in carbonized porous silicon is considered. The model involves processes in a heterojunction between p-Si and p-SiC nanodimensional grains and the interfacial SiO_x and Si_xO_yC_1−x−y layers, where the radiative annihilation of charge carriers takes place. Irrespective of the size of nanograins, the bandgap width in the interfacial layers remains constant, which accounts for the fixed positions of red (1.8 eV) and blue-green (2.4 eV) PL bands observed in the experiment. The dimensions of nanograins were determined using X-ray diffraction and scanning tunneling microscopy.     

铈掺杂多孔硅的形貌和光致发光研究

采用电化学方法在多孔硅中掺杂了稀土铈(Ce)元素.利用原子力显微镜表征了多孔硅和Ce掺杂多孔硅的表面形貌,采用荧光分光计对样品的光致发光(PL)特性进行了研究.多孔硅样品在480nm波长激发下PL谱上观察到两个发光峰,分别位于572和650nm;通过光致发光激发谱测量,得到位于572、650nm的发光峰对应的最佳激发波长分别为380和477nm.Ce掺杂多孔硅样品在480nm波长激发下,PL谱上只显示出多孔硅原有的发光增强;而在380nm波长激发下的PL谱上不仅显示多孔硅原有的发光增强,而且还出现了新的发光峰位于517nm.认为这分别是Ce3 与nc-Si发生了能量传递和Ce掺杂引入了新的发光中心所造成的.     

Crystallite-size-dependent characteristics of porous silicon

Porous silicon prepared with anodic currents of 5 to 30 mA/cm² are characterized for structural and electronic properties of surface using photoluminescence, grazing angle X-ray diffraction, photoconductivity, thermally stimulated exo electron emission and work function measurements. The observed results indicate that with increasing porosity the crystallite size decreases and the amount of silicon hydride and oxide-type species increases, exhibiting a tendency similar to that of hydrogenated amorphous silicon and hydrogenated microcrystalline silicon. Free-standing powder of porous silicon, characterized by bright photoluminescence at 730 nm, showed crystallites of nanometre dimensions under the transmission electron microscope.     

The synthesis and photoluminescence properties of selenium-treated porous silicon nanowire arrays

Here we prepared vertical and single crystalline porous silicon nanowire (SiNW) arrays using the silver-assisted electroless etching method. The selenization was carried out by annealing the samples in vacuum with selenium atmosphere. The selenization treatment at 700?°C is useful for investigating the photoluminescence (PL) properties of porous SiNWs, with an enhancement of 30 times observed. The observed PL peaks blue-shift to 650 nm and the decomposition of the spectrum reveals that three PL bands with different origins are obtained. It is proved that selenization treatment could remove the Si-H bonds on the surface and form Si-Se bonds, which could increase the absorbance of the SiNWs and also enhance the stability of the PL intensity. These Se-treated porous SiNWs may be useful as nanoscale optoelectronic devices.     

浸泡后多孔硅的结构及光致发光特性

用电化学腐蚀方法制备了多孔硅样品,在浸泡液中浸泡使其表层多孔层与样品分离,在样品表面形成了丰富的SiO2包裹纳米硅颗粒结构,研究了样品的光致发光(PL)特性.结果表明,与剥离前相比,表层多孔层剥离后PL谱的强度约有10倍的增幅,峰位主要在蓝紫光范围内.在300℃干氧中退火后,样品的发光强度下降为退火前的三分之一,随着退火温度的升高,发光强度有所增强.退火前后有不同的发光机理,退火前光激发主要在纳米硅内,然后在二氧化硅层中的发光中心辐射复合;退火后光激发和光辐射都发生在二氧化硅层中.     

Argon-oxygen ion-plasma treatment modifies the surface composition and photoluminescence spectrum of porous silicon

We have studied changes in the surface composition and photoluminescence spectrum of porous silicon (por-Si) during the ion-plasma etching of samples in an argon-oxygen gas mixture. This treatment leads to the passivation of the surface of quantum filaments by residual fluorine and the formation of silicon oxide. The source of fluorine atoms are HF molecules retained in the volume of pores upon the por-Si structure formation by chemical etching. Increase in the fluorine concentration is accompanied by the growth in intensity of the blue-green band and broadening of the red band in the photoluminescence spectrum of por-Si.     

Activation energy of electron-stimulated quenching of the photoluminescence of n-type porous silicon

The degradation of photoluminescence of porous silicon by kilovolt electrons and the mechanism and activation energy of this process have been investigated. Quantitative relations between the integral intensity of the photoluminescence and the irradiation dose and substrate temperature are obtained. The mechanism of the process is discussed and its activation energy is determined. Pis’ma Zh. Tekh. Fiz. 23, 44–50 (September 26, 1997)     

Effect of annealing in various atmospheres on the photoluminescence of porous silicon

The effect of isochronous annealing in various atmospheres on the photoluminescence of porous p-type silicon samples obtained by anodization under identical conditions was studied. Comparative experimental data for the samples annealed in air, nitrogen, and vacuum are presented.     

Anomalous character of the decay kinetics of the photoluminescence of carbonized porous silicon

The time dependence of the decay of the photoluminescence of porous silicon subjected to high-temperature carbonization (1000–1200 °C) and simultaneously doped with B, P, Ga, or Al atoms is investigated. The boron-doped samples show an anomalously long decay time for the blue-green (2.4 eV) photoluminescence band. In addition, in this case oscillations with a period of 50 ms are observed in the photoluminescence decay curve. Pis’ma Zh. Tekh. Fiz. 25, 13–20 (26 March 1999)     

Surface and optical characterization of the porous silicon textured surface

In the present studies, the structural and optical properties of the electrochemically etched PS layers are presented. The formation conditions under constant anodization current density was varied to get a variety of PS samples to analyze the structural and optical characteristics of the porous silicon layers and, then to correlate the resultant surface morphology with the etching process. The low-porosity PS layers thus formed on the silicon substrate have a refractive index value (n_ps = 1.9), which is an intermediate value between bulk silicon substrate (n_Si = 3.4) and air (n_air = 1.0). The results of diffused reflectance, surface morphology by atomic force microscopy (AFM), and Raman scattering measurements show that the resultant surface morphology of the PS layers consist of irregular and randomly distributed nanocrystalline Si structures. The reduction in reflection of the low porosity porous silicon layers is due to light scattering and light trapping of the incoming light by total randomization of the incoming light within the PS structure. The Fourier transform infrared (FTIR) measurements on the PS layer on Si substrate show that PS surface is characterized by chemical species like Si—H and Si—O etc., co-existing on the surface. The presence of hydrogen-related species on the PS layer can provide to some extent a surface passivation effect.     

Link between O2SiH infrared band amplitude and porous silicon photoluminescence during ambient O3 oxidation

We carefully evaluate how porous silicon (pSi) surface oxidation by ozone (O(3)) and the resulting changes in nanocrystallite surface chemistries (e.g., SiOSi, SiH(x) (x = 1-3), O(y)SiH (y = 1-2), and SiOH) influence the pSi photoluminescence (PL). We discover a relationship between the pSi PL and the O(2)SiH band amplitude.     

On the relationship between radiation-stimulated photoluminescence and nitrogen atoms in p-4H-SiC

Photoluminescence (PL) appearing in p-4H-SiC upon its electron irradiation has been studied. A model that accounts for the dependence of the PL intensity on the irradiation dose is suggested. The conclusion is drawn that nitrogen–radiation defect donor–acceptor pairs are PL activators.     

UV photooxidation induced structural and photoluminescence behaviors in vapor-etching based porous silicon

In this paper, we investigate the effect of UV irradiation on Vapor-Etching (VE) based Porous Silicon (PS) structure and luminescence under controlled atmosphere (N₂, air, O₂). The oxidation evolution is monitored by Fourier transform infrared (FTIR) spectroscopy. FTIR measurements show that the SiH_x bond, initially present in the freshly prepared PS layers, decreased progressively with UV irradiation time until they completely disappear. We found that this treatment accelerates the oxidation process. SiO_x structures appear and gradually become dominant as regard to the SiH_x species, while UV irradiation is in progress. Generally, the photoluminescence (PL) intensity of the PS layer decreases instantaneously at the starting by the UV excitation and stabilizes after a period depending on the ambient gas and the specific surface area of the porous structure. Further UV exposure leads to a linear decrease of the PL intensity due to change of surface passivation from SiH_x to O_ySiH_x. After less than 100 min of UV irradiation, the PL intensity exhibits an exponential decay. UV exposure in air and O₂ leads approximately to the same PL behavior, although faster PL intensity decrease was observed under O₂-rich ambient. This was explained as being due to intense hydrogen desorption in presence of oxygen. Correlations of PL results with FTIR measurements show that surface passivation determine the electronic states of silicon nano-crystallites and influence the photoluminescence efficiency.     

Enhanced photoluminescence from porous silicon passivated with an ultrathin aluminum film

The photoluminescence (PL) of the porous silicon (PS) can be enhanced by coating it with an ultrathin aluminum (Al) film. The PL intensity of PS was found to increase up to ~ 67% by radio frequency (RF) sputter deposition of 5.2 nm Al film on PS. Fourier transform infrared (FTIR) spectroscopy analysis results suggest that the PL enhancement is related to change of Si–H and Si–O–Si bonds into Si–Al bonds as well as the increase in the carrier concentration participating in the radiative recombination under photoexcitation. On the other hand, the PL of the Al-passivated PS was found to be significantly deteriorated by postannealing owing to the thermal oxidation of the Al layer during annealing.     

Structural and luminescent characteristics of macro porous silicon

The results of structural and luminescent study of porous Si prepared by electrochemical etching and containing the pores of micron sizes are presented. The samples demonstrate bright luminescence with external quantum efficiency of 15–20%. Raman scattering spectra contain only one line corresponding to bulk silicon. Atomic force microscopy image shows the structural elements essentially larger than quantum confinement crystallites. However, X-ray diffraction measurements demonstrate the presence of strained Si quantum confinement nanowires. It is shown that the recombination through interface oxide-related centers of the carriers excited due to light absorption in quantum confinement nanowires gives an essential contribution to emission spectra.