Nondegrading Photoluminescence in Porous Silicon

Abstract

Porous silicon (PS) with nondegrading photoluminescence (PL) was prepared by a novel method. For fresh samples, the PL peak intensity is 2 -2.5 times stronger than that in normal PS. Upon exposing PS to ambient air, the PL intensity increases during the first four months and then saturates. No PL degradation is observed for eight months, and the peak position remains unchanged. The same effect can also be achieved by annealing treatments. This PL stability is attributed to the formation of stable Fe-Si bonds on the surface of PS. Exploration of the mechanism provides strong proof of the quantum confinement model of the luminescence of PS. [S0031-9007 (98)06914-2] PACS numbers: 78.55.Mb, 81.05.RmThe discovery of light-emitting porous silicon (normal PS) [1] has made it possible to develop Si-based optoelectronic devices. In recent years, most of the research has been directed at understanding the origin of the luminescence [1-8] and fabricating PS-based light emitters [9][10][11][12]; but the problems of the degradation [2,13,14] and the relatively low efficiency [15] of the photoluminescence (PL) remain unsolved. The PL degradation subsequent to normal PS preparation, accompanied with a blueshift of the peak position, is generally believed to originate from the chemical instability of the PS surface [2,13,14]. Under the attack of oxygen, the Si-H bonds on the surfaces of the Si nanocrystallites will be broken and the quantity of the Si dangling bonds will increase. This variation will ultimately lead to the degradation of the PL intensity [13,14]. On the other hand, deep oxidation will reduce the sizes of the Si nanocrystallites and result in the blueshift of the PL peak position [13,14]. The motivation of this research is to try to construct a stable Fe-Si bond on PS surface to substitute the easily broken Si-H bond and thereby realize the stabilization of the intensity as well as the peak position of the PL of PS.The PS samples reported here were prepared by a hydrothermal method which was first adopted by Chen et al. in preparing normal PS [16], but with a different solution. The initial materials were P͞P 1 -type boron-doped single crystal Si wafers with (111) orientation and ϳ1.5 2.0 V cm resistivity. The solution for hydrothermal treatment was composed of 40% (weight) hydrofluoric acid and 0.3 mol͞l ferric nitrate aqueous solution according to 7:6 (volume) and the treatment was performed at 140 ± C for 50 minutes. We name as-prepared PS samples as iron-passivated PS. For comparison, normal PS samples were also prepared by the hydrothermal method, but here the Si wafers were treated at 170 ± C for 4 hours in a solution of 15 mol͞l hydrofluoric acid.The PL spectra of all these samples were measured with an 850-type visible-ultraviolet spectrophotometer (Hitatchi, Japan) at room temperature, and these results were corrected for the system response. Here the most efficient wavelengths for excitation were adopted as the excitation wavelengths, 320 nm for iron-passivated PS and 280 nm for normal PS. For both fre...

Optical Characterization of Ultrasmall Si Nanoparticles Prepared through Electrochemical Dispersion of Bulk Si

“…The analysis has generally focused on the source of PL and the debate between the quantum confinement (delocalized) and surface state (localized) mechanisms. Researchers studying porous Si structures, [40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57] for example, have attributed the PL to various sources ranging from quantum-confined nanorods and nanodots [44][45][46] to surface state silanone and siloxane groups. [47][48][49][50][51][52][53][54][55][56] For Si and Ge nanoparticles prepared through various routes such as solution-phase synthesis, [1][2][3][4][8][9] electrochemical etching, 10-13 laser ablation, 14,15 and using supercritical fluids, [16][17][18] the suggested PL sources have ranged from delocalized quantum confinement states 15 to localized SiSi surface dimer states.…”

Biosensors Based on the Photoluminescence of Porous Silicon. Overall Characteristics and Application

“…Благодаря такой обработке интен-сивность ФЛ ПК возрастала, причем в случае использования растворов хлоридов металлов она увеличивалась при увеличении их концен-трации. Модификация ПК [29,30] гидротер-мической обработкой в растворе, содержащем HF и Fe(NO 3 ), на протяжении 45-50 минут при 140-142 °С приводит к сильной и стабильной ФЛ.…”

Surface Stability studies of Porous Silicon with Si-Ag Bonds

“…This compelled the researchers to look into this fundamental problem with a view to arrest the cause by evolving new concept and technology. Numerous treatments to stabilize porous silicon structure have been reported like chemical treatment [13] [14], carbonization [15], thermal treatment [16] [17] and photo-induced electrochemical anodization method [18], but till date no method have shown any long term surface stability of porous silicon. In this report, authors have carried out the two step method viz chemical followed by electrochemical method on the PS samples to prepare Si-Ag bonds on the PS surface.…”