Influence of LiBr on photoluminescence properties of porous silicon

A new method has been developed to improve the photoluminescence intensity of porous silicon (PS), which is first time that LiBr is used for passivation of PS. Immersion of the PS in a LiBr solution, followed by a thermal treatment at 100 °C for 30 min under nitrogen, leads to a nine fold increase in the intensity of the photoluminescence. The atomic force microscope (AFM) shows an increase of the nanoparticle dimension compared to the initial dimension of the PS nanostructure. The LiBr covers the nanoparticles of silicon without changing the wavelength distribution of the optical excitation and emission spectra. Moreover, a significant decrease of reflectivity was observed for the wavelength in the range of 350-500 nm.     

Effects of thermal oxidation on the photoluminescence properties of porous silicon

The effects of thermal oxidation on the photoluminescence (PL) properties of powdered porous silicon (PSi) are studied using X-ray photoelectron spectroscopy (XPS). It is found that the PL intensity is steeply quenched after annealing at and recovered at above . The XPS intensity of oxides formed on the PSi surface is also found to strongly depend on the annealing temperature. The comparison between the annealing temperature dependence of PL intensity and that of the oxide XPS intensity suggests that the formation of thin disordered SiO₂ layer accompanies the quenching of the PL intensity, and that the formation of thick high-quality SiO₂ layer results in the PL intensity recovery. These results indicate that the thickness and quality of SiO₂ layer play a crucial role in the PL properties of thermally oxidized PSi.     

Improvement of photoluminescence properties of porous silicon by silica passivation

Porous silicon (PS) was passivated by silica film using a sol-gel method; the photoluminescence (PL) properties were significantly improved; namely, PL intensity and stability increased and PL peak shifted to shorter wavelength. Scanning electron microscope (SEM) and Fourier transformed infrared spectroscope (FTIR) results indicated that silica passivation produced a compact film on the PS surface and modified the surface state of PS. The number of stable surface bonds (HSiO₃, HSiSiO₂ and H₂SiO₂) increased due to the oxidation of SiH back-bonds during the gelation process, and thus the PL intensity and stability were improved. Moreover, the blue-shift of PL peak was determined due to the increase in the ratio of SiO/SiH.     

Effects of selenium treatment on composition and photoluminescence properties of porous silicon

In this work, an ultrasonically enhanced anodic electrochemical etching is developed to fabricate light-emitting porous silicon material. Porous silicon layer is fabricated in n-type (1 0 0) oriented silicon using HF solution and treated in selenious acid to increase the photoluminescence intensity. It is found that the increase of photoluminescence intensity after selenious acid treatment is higher in the intact zones and lower in the detached zones of ultrasonic excitation. The photoluminescence appears as a non-monotonous function of time exposure of selenious acid treatment. Surface chemical composition analysis by X-ray photoelectron spectroscopy shows formation of Si-Se_x and Si-Se_x-O_y on the surface of porous silicon treated with the selenious acid.     

多孔硅的时间延迟光谱

利用时间延迟光谱技术测量了多孔硅的发光光谱. 实验结果表明,多孔硅的发光是复杂的动力学发光弛豫过程,时间延迟光谱测量技术在研究复杂动力学发光过程方面比稳态光谱测量方法更有效.     

Method of porous diamond deposition on porous silicon

In this paper, we discuss the experimental results of the fabrication of porous diamond/porous silicon and porous diamond structures by chemical vapor deposition of diamond over a skeleton of porous silicon, replicating the porous surface geometry around the Si pores and also creating new porous diamond structures. Scanning electron microscopy (SEM) revealed that the diamond nuclei are deposited on the top of the porous silicon skeleton, forming isolated grains in the first nucleation stages, and then growing like the usual structure of most ceramic materials, making a self-sustained porous diamond structure. Raman spectroscopy revealed that the diamond films are of good quality, close to that of diamond films grown on crystalline silicon.     

Instability of the photoluminescence of porous silicon

Results of studies of the photoluminescence of porous silicon with different prehistories have revealed the mechanism and nature of the instability of the luminescence properties of freshly prepared samples. It was established that the initial quenching and subsequent rise of the photoluminescence is attributable to the intermediate formation of silicon monoxide (photoluminescence degradation) and subsequent additional oxidation to form SiO₂ (photoluminescence rise). Ultraviolet laser irradiation accelerates this process by a factor of 200–250 compared with passive storage of the samples in air. Plasma-chemical treatment in an oxygen environment merely results in a subsequent rise in the photoluminescence as a result of the formation of monoxide on the porous silicon surface. A kinetic model is proposed for this process. Zh. Tekh. Fiz. 69, 135–137 (June 1999)     

Influence of natural aging on photoluminescence from porous silicon

The influence of natural aging on the photoluminescence intensity and the position of a photolu-minescence peak in n-type por-Si (por-Si) is studied. The variation of the phase composition and the relative content of the amorphous and oxide phases of silicon in por-Si during aging is determined by fitting simulated spectra to experimental ultrasoft Si L _2,3 X-ray emission spectra using reference spectra.     

Improvement of photoluminescence and electrical properties of porous silicon layer treated with lanthanum

The influence of surface treatment of porous silicon (PS) in lanthanum (La) containing solution during different times on its photoluminescence and electrical properties has been investigated. For this purpose, chemical composition, structural, vibrational, photoluminescence and electrical characteristics of the porous silicon layer with and without lanthanum were examined using X-ray diffractometry (XRD), energy dispersive X-ray (EDX) spectroscopy, Fourier transmission infrared (FTIR) spectroscopy, photoluminescence (PL) spectroscopy and current–voltage (I–V) measurements. The results indicate that porous silicon layers treated with lanthanum exhibit an enhancement of photoluminescence intensity and show an improvement current intensity compared to untreated porous silicon layer.     

Stable blue-green and ul traviolet photoluminescence from silicon carbide on porous silicon

β-Silicon carbide layers have been prepared by high temperature pyrolysis of polyimide Langmuir-Blodgett films on porous silicon substrate in vacuum. The formation of silicon carbide is confirmed by the IR and XRD spectra. It is found that photoluminescence still exists and appears in the blue-green and ultraviolet regions after thermal treatment at 900°C. These results indicate that the silicon carbide layers, which are formed, are responsible for the blue-green luminescence.     

Effects of thermal annealing and ageing on porous silicon photoluminescence

Effects of vacuum and ambient thermal annealing and ageing on the photoluminescence (PL) spectra of porous silicon (po-Si) have been investigated. Isochronal anneals up to 300°C were done and PL spectra were recorded and compared to the un-annealed specimens. Minimal changes are induced for anneals below approximately 125°C; however, significant reduction in PL intensity occurs following anneals at T?≥?200°C. Deconvolution of the PL spectra into five distinct Gaussian bands reveals that at least two of the bands are attributable to non-quantum confinement mechanisms. Specifically, bands appearing at 1.58 and 1.78?eV are ascribed to non-bridging oxygen hole related defects. Recovery of PL intensity following thermal annealing occurs over a period of several days at a rate that is dependent upon annealing temperature and environment. Passivation of Si dangling bonds on the po-Si surface via effusion of hydrogen and incorporation of oxygen is responsible for the observed variations in PL intensity.     

Stable ultraviolet photoluminescence emission in n-type porous silicon

This very paper is focusing on the investigation of porous silicon preparation with n-type silicon wafer by means of electrochemical anodization in the dark and, particularly, on its stable ultraviolet photoluminescence emission. A lateral electrical potential was applied, for this purpose, on silicon wafers, driving the electrons away and letting holes appear on the surface of the silicon wafer to enhance the electrochemical etching process. Characterizations have been made with scanning electronic microscope, fluorescence spectrophotometer and Fourier transform infrared spectroscope. An ultraviolet photoluminescence emission of 370 nm is found in the as-prepared n-type porous silicon, which seems to be well associated with the formation of oxygen-related species (twofold coordinated silicon defect) during the anodic oxidation. The result characterized by photo-bleaching performance indicates that the ultraviolet photoluminescence emission is so stable—only 7% reduction within 3600 s. Meanwhile the morphology of as-prepared n-type porous silicon is investigated.     

稀土掺杂多孔硅的蓝光发射

关键词：     

Tunable photoluminescence of porous silicon by liquid crystal infiltration

The photoluminescence (PL) of porous silicon films has been investigated as a function of the amount of liquid crystal molecules that are infiltrated into the constricted geometry of the porous silicon films. A typical nematic liquid crystal 4-pentyl-4′-cyanobiphenyl was employed in our experiment as the filler to modify the PL of porous silicon. It is found that the originally red PL of porous silicon films can be tuned to blue by simply adjusting the amount of liquid crystal molecules in the microchannels of the porous films. The chromaticity coordinates are calculated for the recorded PL spectra. The mechanism of the tunable PL is discussed. Our results have demonstrated that the luminescent properties of porous silicon films can be efficiently tuned by liquid crystal infiltration.     

Long-time stabilization of porous silicon photoluminescence by surface modification

We present results on the photoluminescence (PL) properties of porous silicon (PS) as a function of time. Stabilization of PL from PS has been achieved by replacing silicon-hydrogen bonds terminating the surface with more stable silicon-carbon bonds. The composition of the PS surface was monitored by transmission Fourier transform infrared (FTIR) spectroscopy at intervals of 1 month in ageing time up to 1 year. The position of the maximum PL peak wavelength oscillates between a blue-shift and a red-shift in the 615-660 nm range with time.     

有机吸附物对多孔硅微腔发光的影响

理论上,采用Bruggeman有效介质近似,研究了有机吸附物对多孔硅微腔的折射率及其光致发光谱的影响.实验上,采用计算机控制的电化学腐蚀法制备了多孔硅微腔样品,并利用机械泵油的蒸气分子与该微腔样品进行相互作用.研究发现,多孔硅微腔发射的窄化光致发光谱对泵油蒸气分子的吸附与脱附很敏感,与之伴随的是该窄化光致发光谱发生明显的峰位移动(可达71nm)和强度变化.结合Bruggeman近似和表面态对多孔硅发光的影响,对实验结果进行了定性解释.实验结果与理论模拟结果符合较好. 关键词： Bruggeman近似 吸附物 多孔硅微腔 光致发光谱     

Influence of alkali metallization (Li, Na and K) on photoluminescence properties of porous silicon

We present results for alkali metallization effects on photoluminescence (PL) properties of porous silicon (PS). The metallization of PS was realized by immersion plating in solutions containing 3 mM LiNO₃, KNO₃ and NaNO₃ metal salts. The surface bond configuration of PS was monitored by Fourier transmission infrared spectroscopy (FTIR) and it was found that the PS surface was oxidized after metallization. Surface properties of PS were investigated by field emission scanning electron microscopy (FE-SEM) and it was found that the PS surface was covered by alkali metals for short immersion times. The PL intensity increased for critical immersion times and PL spectrum shifted to high energy region with the metallization. The experimental results suggest a possibility that the metallization provides a relatively easy way to achieve an increase in the PL intensity and oxidation of the PS surface.