Photoluminescence of Anisotropically etched silicon

Visible room-temperature luminescence of Anisotropically Chemically Etched (ACE) silicon under spontaneous chemical surface modification in HNO₃:HF solution is reported. The material is investigated by SEM, AES, IR transmission and Raman scattering methods.     

飞秒脉冲激光辐照对硅发光性能的影响

利用飞秒脉冲激光对单晶硅进行辐照,研究了在不同环境(纯水和空气)和能量密度条件下激光刻蚀过后硅片的光致荧光特性.对于辐照后的硅片,利用了场发射扫描电子显微镜(FESEM)、能谱仪(EDS)、傅里叶红外光谱仪(FT-IR)、光致荧光光谱仪(PL)进行表征.结果显示:在空气中样品表面形成了条纹状微结构,纯水中硅片表面生成了尺寸更小的珊瑚状微结构;激光刻蚀后在硅片表面的生成物主要是SiOx(x2),在纯水中处理后硅片氧元素的含量接近是空气中的4倍;傅里叶变换红外透射谱中主要为Si—Si键(610 cm-1)和Si—O—Si键(1105 cm-1)的振动;在空气和纯水中激发出的荧光均为蓝光(420—470 nm),在各自最佳激发波长下,纯水中荧光强度比空气中强2到3倍,但是在可见光范围内荧光峰的位置和形状都基本没有发生变化.研究表明:氧元素在光致发光增强上起着重要作用,光致发光最主要是由形成的氧缺陷SiOx(x2)导致的,生成低值氧化物SiOx的多少决定了发光的强弱.     

Photoluminescence and electroluminescence from porous silicon

The properties and origins of the red, blue and infrared photoluminescence bands of porous silicon are reviewed and discussed in the light of the models that have been proposed to explain the experimental and theoretical results. The red band is due to quantum confinement possibly supplemented by surface states; the blue band is linked to the presence of silicon dioxide; the infrared band is correlated with dangling bonds and bandgap luminescence in large crystallites. The fabrication and characterization of light-emitting devices made of porous silicon are reported and discussed with respect to critical issues such as the device stability, efficiency, modulation speed, emission wavelength, and compatibility with microelectronic processing.     

Photoluminescence studies of porous silicon microcavities

Narrow photoluminescence peaks with a full-width at half-maximum of 14–20 nm are obtained from porous silicon microcavities (PSM) fabricated by the electrochemical etching of a Si multilayer grown by molecular beam epitaxy. The microcavity structure contains an active porous silicon layer sandwiched between two distributed porous silicon Bragg reflectors; the latter were fabricated by etching a Si multilayer doped alternatively with high and low boron concentrations. The structural and optical properties of the PSMs are characterised by scanning electron microscopy and photoluminescence (PL). The wavelength of the narrow PL peaks could be tuned in the range of 700–810 nm by altering the optical constants.     

Photoluminescence characterization of silicon nanostructures embedded in silicon oxide

This paper describes a simple method to analyze the photoluminescent characteristics of materials based on embedded light-emitting nanoclusters. Photoluminescence spectra of deposited silicon sub-oxide layers with the same composition and different thicknesses have been obtained. A saturation of the total luminescence intensity is observed with increase in thickness. By analyzing the photoluminescence spectra several optical and structural parameters can be evaluated. We thus propose a model in which the absorption of light from a nanostructure layer implies the possibility of subsequent luminescence and affects the underlying layers as well. By fitting the data to the developed model, two fundamental parameters are extracted: nanostructures absorption probability, which is independent of the emission energy and the spectra of emission probability of an excited nanostructure which fits a Gaussian shape.     

Photoluminescence evolution in self-ion-implanted and annealed silicon

Si⁺ ion-implanted silicon wafers are annealed at different temperatures from room temperature to 950~℃ and then characterized by using the photoluminescence (PL) technique at different recorded temperatures (RETs). Plentiful optical features are observed and identified clearly in these PL curves. The PL spectra of these samples annealed in different temperature ranges are correspondingly dominated by different emission peaks. Several characteristic features, such as an R line, S bands, a W line, the phonon-assistant W^\rm TA and Si^\rm TO peaks, can be detected in the PL spectra of samples annealed at different temperatures. For the samples annealed at 800~\du, emission peaks from the dislocations bounded at the deep energy levels of the forbidden band, such as D_1 and D₂ bands, can be observed at a temperature as high as 280~K. These data strongly indicate that a severe transformation of defect structures could be manipulated by the annealing and recorded temperatures. The deactivation energies of the main optical features are extracted from the PL data at different temperatures.     

Enhancement of the photoluminescence of silicon nanocrystals under the influence of electric field

The effect of electric field generated by the application of surface acoustic waves on photoluminescence (PL) of silicon nanocrystals embedded in SiO₂ films is studied. It is shown that the application of electric field results in an increase in the intensity of nanocrystal PL, the increase amounting to 10% at a field amplitude of 6 kV cm⁻¹. The results are discussed within the frame of the self-trapped exciton model.     

Photoluminescence and paramagnetic defects in silicon-implanted silicon dioxide layers

Thermally grown SiO₂ layers on Si substrates implanted with Si⁺ ions with a dose of 6×10¹⁶ cm⁻² were studied by the techniques of photoluminescence, electron paramagnetic resonance (EPR), and low-frequency Raman scattering. Distinct oxygen-vacancy associated defects in SiO₂ and non-bridging oxygen hole centers were identified by EPR. The luminescence intensity in the 620 nm range was found to correlate with the number of these defects. The low-frequency Raman scattering technique was used to estimate the average size of the Si nanocrystallites formed after the implantation and thermal annealing at T>1100°C, which are responsible for the photoluminescence band with a maximum at 740 nm. The intensity of this band can be significantly enhanced by an additional treatment of the samples in a low-temperature RF plasma.     

Enhancement of the emission yield of silicon nanocrystals in silica due to surface passivation

The ability of surface passivation to enhance the photoluminescence (PL) emission of Si nanocrystals in SiO₂ has been investigated. Silicon precipitation in implanted samples takes place in a time scale of few minutes at 1100°C. For longer annealing at the same temperature, the PL intensity of the Si nanocrystals increases and eventually reaches saturation, while it correlates inversely with the amount of Si dangling bonds at the Si–SiO₂ interface (P_b centers), as measured by electron spin resonance. This combined behavior is independent on the silica matrix properties, implantation profiles and annealing atmosphere and duration. The observation that the light emission enhancement is directly related to the annealing of P_b centers is confirmed by treatment in forming gas. This mild hydrogenation at much lower temperature (450°C) leads to a complete passivation of the P_b defects, increasing at the same time the PL yield and the lifetime.     

Photoluminescence from Er-doped silicon rich oxide thin films

 Photoluminescence (PL) properties of Er-doped silicon rich oxide thin films deposited on Si substrate by co-evaporation of silicon monoxide and Er under different atmospheres are investigated. The samples exhibit luminescence peak at 1.54 μm which could be assigned to the recombination in intra-4f Er³⁺ transition. PL shows that this transition is highest when ammonia atmosphere is used during deposition followed by an annealing temperature at 850 °C in 95% N₂+5% H₂ gas (forming gas). In fact, we believe that the presence of the N atoms around Er ions increases the intensity of the 1.54 μm luminescence.     

Structure and optical features of silicon carbide nanocrystals confined in alumina matrices

Thin films based on silicon carbide and alumina were synthesized by means of rf-sputtering using a co-deposition process. Several nanostructures were created which consist of thin films (∼200 nm thick) with homogeneous distribution of SiC nanocrystals (∼5 nm mean diameter) in the host alumina matrices. Characterization methods including X-ray photoelectrons spectroscopy (XPS), UV-vis absorption and photoluminescence (PL) were used to identify the involved structures, compositions and optical features of these nanostructures. Thus, XPS investigations were relevant to point out the involved chemical bonding in the core SiC nanocrystals and in the host alumina environments. Additionally, mixed bonding such as Si-O-C was also shown and seems to correlate with the SiC-alumina interfaces. Optical properties of the nanostructures films such as UV-vis absorption and photoluminescence (PL) were measured in representative samples and compared to simulated PL responses obtained by a theoretical model.     

Photoluminescence and optical absorption properties of silicon quantum dots embedded in Si-rich silicon nitride matrices

Silicon nitride (SiN_x) films were prepared with a gas mixture of SiH₄ and NH₃ on Si wafers using the plasma-enhanced chemical vapor deposition (PECVD) method. High-resolution transmission electron microscopy and infrared absorption have been used to reveal the existence of the Si quantum dots (Si QDs) and to determine the chemical composition of the silicon nitride layers. The optical properties of these structures were studied by photoluminescence (PL) spectroscopy and indicate that emission mechanisms are dominated by confined excitons within Si QDs. The peak position of PL could be controlled in the wavelength range from 1.5 to 2.2 eV by adjusting the flow rates of ammonia and silane gases. Absorbance spectra obtained in the transmission mode reveal optical absorption from Si QDs, which is in good correlation with PL properties. These results have implications for future nanomaterial deposition controlling and device applications.     

Photoluminescence studies on porous silicon/polymer heterostructure

Hybrid devices formed by filling porous silicon with MEH-PPV or poly [2-methoxy-5(2-ethylhexyloxy-p-phenylenevinylene)] have been investigated in this work. Analyses of the structures by scanning electron microscopy (SEM) demonstrated that the porous silicon layer was filled by the polymer with no significant change of the structures except that the polymer was infiltrated in the pores. The photoluminescence (PL) of the structures at 300 K showed that the emission intensity was very high as compared with that of the MEH-PPV films on different substrates such as crystalline silicon (c-Si) and indium tin oxide (ITO). The PL peak in the MEH-PPV/porous silicon composite structure is found to be shifted towards higher energy in comparison with porous silicon PL. A number of possibilities are discussed to explain the observations.     

Photoluminescence analyses of hydrogenated amorphous silicon nitride thin films

Silicon-rich hydrogenated amorphous silicon nitride (a-SiN_x:H) films were grown by plasma enhanced chemical vapor deposition (PECVD) with different r=NH₃/SiH₄ gas flow ratios. The optical absorption characteristics were analyzed by Fourier transform infrared (FTIR) and UV-visible transmittance spectroscopies. The recombination properties were investigated via photoluminescence (PL) measurements. As r was increased from 2 to 9, the PL emission color could be adjusted from red to blue with the emission intensity high enough to be perceived by naked eye at room temperature. The behaviors of the PL peak energy and the PL band broadness with respect to the optical constants were discussed in the frame of electron-phonon coupling and band tail recombination models. A semiquantitative analysis supported the band tail recombination model, where the recombination was found to be favored when the carriers thermalize to an energy level at which the band tail density of states (DOS) reduces to some fraction of the relevant band edge DOS. For the PL efficiency comparison of the samples with different nitrogen contents, the PL intensity was corrected for the absorbed intensity fraction of the incident PL excitation source. The resulted correlation between the PL efficiency and the subgap absorption tail width further supported the band tail recombination model.     

Photoluminescence of porous silicon surfaces stabilized through Lewis acid mediated hydrosilylation

Lewis acid mediated hydrosilylation on porous silicon surfaces permits facile incorporation of a wide variety of functionalities through stable silicon–carbon bonds. The surfaces demonstrate high chemical stability with respect to hydrofluoric acid and aqueous base. The effects of the covalently bound surface groups on photoluminescence have been investigated and it was noted that alkyl and alkenyl termination induced only small decreases in photoluminescence efficiency. Aromatic substituents conjugated through a vinyl group, however, bring about almost complete quenching of the observed photoluminescence, regardless of substitution with either electron withdrawing (chloride) or donating (methyl) functionalities. The photoluminescence fatigue of dodecyl terminated surfaces in air for 12–16 h periods has been monitored and compared to unfunctionalized porous silicon. In air, the photoluminescence of dodecyl terminated surfaces degrades faster than the unfunctionalized porous silicon but under inert atmosphere (nitrogen), the rate of photoluminescence fatigue is slow in both cases and approximately equivalent.     

Luminescence of dense, octahedral structured crystalline silicon dioxide (stishovite)

It is obtained that, as grown, non-irradiated stishovite single crystals possess a luminescence center. Three excimer pulsed lasers (KrF, 248 nm; ArF, 193 nm; F₂, 157 nm) were used for photoluminescence (PL) excitation. Two PL bands were observed. One, in UV range with the maximum at 4.7±0.1 eV with FWHM equal to 0.95±0.1 eV, mainly is seen under ArF laser. Another, in blue range with the maximum at 3±0.2 eV with FWHM equal to 0.8±0.2 eV, is seen under all three lasers. The UV band main fast component of decay is with time constant τ=1.2±0.1 ns for the range of temperatures 16-150 K. The blue band decay possesses fast and slow components. The fast component of the blue band decay is about 1.2 ns. The slow component of the blue band well corresponds to exponent with time constant equal to 17±1 μs within the temperature range 16-200 K. deviations from exponential decay were observed as well and explained by influence of nearest interstitial OH groups on the luminescence center. The UV band was not detected for F₂ laser excitation. For the case of KrF laser only a structure less tail up to 4.6 eV was detected. Both the UV and the blue bands were also found in recombination process with two components having characteristic time about 1 and 60 μs. For blue band recombination luminescence decay is lasting to ms range of time with power law decay ∼t⁻¹.For the case of X-ray excitation the luminescence intensity exhibits strong drop down above 100 K. such an effect does not take place in the case of photoexcitation with lasers. The activation energies for both cases are different as well. Average value of that is 0.03±0.01 eV for the case of X-ray luminescence and it is 0.15±0.05 eV for the case of PL. So, the processes of thermal quenching are different for these kinds of excitation and, probably, are related to interaction of the luminescence center with OH groups.Stishovite crystal irradiated with pulses of electron beam (270 kV, 200 A, 10 ns) demonstrates a decrease of luminescence intensity excited with X-ray. So, irradiation with electron beam shows on destruction of luminescent defects.The nature of luminescence excited in the transparency range of stishovite is ascribed to a defect existing in the crystal after growth. Similarity of the stishovite luminescence with that of oxygen deficient silica glass and induced by radiation luminescence of α-quartz crystal presumes similar nature of centers in those materials.     

Optical properties of GaN nanocrystals embedded into silica matrices

The purpose of this work was to obtain GaN nanocrystals (GaN-nc) embedded into silica-based matrix and to investigate their optical properties by photoluminescence (PL) spectroscopy. GaN-nc have been obtained both by the sol–gel chemistry and by the combustion method (CM). The GaN-nc obtained by CM have been introduced into the silica-based matrix during the formation of the film in the spin-on technique. Strong emission at 3.4 eV has been observed for the films doped by GaN-nc whereas no emission in UV has been observed for GaN-nc obtained by sol–gel chemistry.     

Spectral behavior of the emission around 3.31 eV (A-line) from ZnO nanocrystals

The emission at around 3.31 eV (A-line) from three types of ZnO nanocrystals with different particle sizes (10-1000 nm) was studied. The photoluminescence (PL) measurements were performed under different excitation densities and at different temperatures. The A-line emission exhibited a strong dependence on temperature and excitation power density. With increasing excitation density and temperature overlapping of the closely spaced first longitudinal optical (LO) phonon replica of free excitons by the A-line emission was observed.     

Photoluminescence of CuGaS2 and heterostructure formation with sputtered ZnS

Summary CuGaS₂ crystals grown by iodine transport exhibit room temperature photoluminescences at 2.45 eV and at 1.44 eV. The spectral distribution of the green emission is shown to be relatively well described by the calculated curve for a direct band-to-band transition withk-selection. The heterojunction formation has been tried between sulfur-treated CuGaS₂ crystals and low-resistivity amorphous ZnS films prepared by sputtering at room temperature. TheI–V characteristic of the diode shows rectifying behaviour, but no injection luminescence has been observed. Paper presented at the ?V International Conference on Ternary and Multinary Compounds?, held in Cagliari, September 14–16, 1982.     

SiOx纳米管的制备及其发光特性

以液态金属镓为媒介,利用热蒸发法合成大量非晶SiOx纳米管,这些纳米管管径均匀分布,平均约80 nm,长度大于10μm,且管内外径比例较小．分析发现,在实验过程中,熔入金属镓液滴中的硅元素和氧元素结合并从液滴的表面饱和析出,形成以镓为中心的非晶SiOx纳米管状结构．在室温中,利用260 nm的激发光源激发SiOx纳米管,发现在蓝光波段附近发出强而稳定的PL谱线,这可能与样品中的氧缺陷和空位有关．