On the morphology and the electrochemical formation mechanism of mesoporous silicon

Lehmann, Volker; Stengl, R.; Luigart, A

doi:10.1016/s0921-5107(99)00286-x

Cited by 376 publications

(337 citation statements)

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“…This is more pronounced for the thin pores due to the smaller radius of the curvature at the pore tip. 12 This behavior is observed for both sizes of the small inverted pyramids for lattices A and B. However, the offset is larger for a pit size of 0.56 m than for 0.76 m, which confirms that it is indeed determined by the initial conditions of the structured silicon surface.…”

mentioning

confidence: 51%

Controlled nonuniformity in macroporous silicon pore growth

Matthias¹,

Müller²,

Gösele³

2005

Applied Physics Letters

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Photoelectrochemical etching of uniform prestructured silicon wafers in hydrofluoric acid containing solutions yields periodic structures that can be applied to two-and three-dimensional photonic crystals or microfluidics. Here we demonstrate experimentally macroporous silicon etching initiated by a nonuniform predefined lattice. For conveniently chosen parameters we observe a stable growth of pores whose geometrical appearance depends strongly on the spatially different nucleation conditions. Moreover, we show preliminary results on three-dimensionally shaped pores. This material can be used to realize hybrid photonic crystal structures and incorporate waveguides in three-dimensional photonic crystals. © 2005 American Institute of Physics. ͓DOI: 10.1063/1.2137688͔ Porous silicon, 1,2 and in particular, macroporous silicon, 3,4 has attracted a lot of attention as a unique possibility to structure silicon. 5 This material system has been applied to optical shortpass filters 6 as well as to twodimensional ͑2D͒ and three-dimensional ͑3D͒ photonic crystals. 7,8 All these applications depend on the uniformity of the porous material. This property results from the perfect, lithographically arranged, uniform inverted pyramids acting as nuclei for the pore growth and the self-stabilized photoelectrochemical etching process used. The so-manufactured 3D photonic crystals show complete band gaps of about 5%. Recently, we proposed large 3D photonic band gaps in diamondlike structures, which may be fabricated using complex structured silicon wafers. 9 Here we present a detailed investigation focused on spatially different nucleation conditions. A simple quadratic lattice with a basis of two nonequally sized inverted pyramids is defined. We will demonstrate under which experimental conditions a stable pore growth is observed. Moreover, the nonequally sized nuclei result in a significant initial offset in height between adjacent pores. We will answer the question of how this considerable difference is affected by the selfstabilized interaction between the pores. This approach is well suited to incorporate air defects in photonic band-gap materials in two and three dimensions acting as resonators or waveguides. In particular, this is a step towards the experimental realization of the predicted 2D photonic crystal hybrid structures suggested by Trifonov et al. 10 Typically macroporous silicon is grown in a photoelectrochemical etching process. 5 An arbitrary 2D lattice is defined lithographically on the ͑100͒-oriented n-type silicon wafer. A subsequent anisotropic etching in potassium hydroxide ͑KOH͒ forms inverted pyramids acting as nuclei for the pore growth. This structured frontside is exposed to hydrofluoric acid ͑HF͒. Illuminating the backside of the silicon wafer generates electron-hole pairs. The electrons are extracted by the applied anodic bias whereas the electronic holes-the minority charge carriers-diffuse through the whole wafer to the silicon electrolyte interface. Due to the depletion layer at this interface an e...

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confidence: 51%

Controlled nonuniformity in macroporous silicon pore growth

Matthias¹,

Müller²,

Gösele³

2005

Applied Physics Letters

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“…Lehmann et al 26,27 have reported that the doping density of the substrate determines the pore initiation and also the pore tips, which will be formed in the beginning of anodization process. They discussed that with the control of pore density, it is possible to control the shift of PL peak energy which was demonstrated by the quantum size effect.…”

Section: Resultsmentioning

confidence: 99%

Morphological and optical characteristics of porous silicon produced by anodization process in HF-acetonitrile and HF-ethanol solutions

Miranda¹,

Baldan²,

Beloto³

et al. 2008

J. Braz. Chem. Soc.

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Amostras de silício poroso (PS) foram obtidas pelo processo de anodização em lâminas de Si tipo n, dopadas com fósforo. A oxidação eletroquímica do PS foi obtida utilizando-se solução de ácido fluorídrico (HF) contendo aditivos como etanol e acetonitrila (MeCN). A formação dos poros foi estudada com a variação da resistividade das laminas de Si e parâmetros de processo como: concentração do ácido, densidade de corrente e tempo de anodização. As técnicas de Microscopia Eletrônica de Varredura (MEV) e Espectroscopia de Espalhamento Raman foram utilizadas para a investigação da morfologia e fotoluminescência, respectivamente. A camada de PS formada com o uso da solução de HF-MeCN mostrou maior uniformidade e homogeneidade na distribuição dos macroporos com diferentes tipos e tamanhos. Esse comportamento pode ser explicado devido a tensão superficial da MeCN ser maior que a do etanol. Consequentemente, as moléculas de MeCN podem passivar a superfície do silício durante o processo de anodização.Porous silicon (PS) samples were obtained by anodization etching process of n-type silicon wafer phosphorus-doped. Electrochemical oxidation of PS was investigated in aqueous hydrofluoric acid (HF) containing additive such as ethanol or acetonitrile. Pore formation was studied with the variation of type and resistivity of the silicon wafer, taking into account the most important anodization process parameters such as: acid concentration, current density and anodization time. Scanning Electron Microscopy (SEM) and Raman Scattering Spectroscopy measurements were used to characterize the macropore morphology changes and sample photoluminescense responses, respectively. PS layer formed in HF-acetonitrile solution showed more uniform and homogeneous macropore distributions with different shapes and sizes. Behavior may be explained because acetonitrile surface tension is greater than that of ethanol. Therefore, acetonitrile molecules might passivate the silicon surface dissolved during the anodization process. Keywords: porous silicon, HF-acetonitrile, HF-ethanol IntroductionSince the discovery of its visible photoluminescence (PL) at room temperature, porous silicon (PS) has been intensively studied. Nowadays, PS is considered a very attractive material for the sensing layer in a chemical sensor, sacrificial layer in micromachining, and light emitting diode (LED) in optoelectronic devices. [1][2][3][4] Porous Si might be formed by electrochemical etching of single monocrystalline Si in HF solutions containing additives as ethanol or acetonitrile (MeCN). However, the anodization process was firstly studied by Bomchil et al., 5 in 1983, using HF and ethanol solution and they reported that ethanol improved the homogeneity of PS layer. Consequently, HF-ethanol has been used by most research groups as the standard electrolyte for PS formation process. After that, Propst et al. 6 have reported the electrochemical oxidation of p-and n-type silicon in nonaqueous electrolyte of HF-MeCN and discussed their singular and large porous structure...

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“…It takes place in hydrofluoric acid (HF) solution, where the silicon is dissolved by the fluorine ions thanks to the positive charges reaching the electrolyte/silicon interface (Kochergin & Föll, 2009;Lehmann & Gösele, 1991). Depending on substrate doping, current density and electrolyte concentration, the porosity and morphology of the fabricated PSi can be varied (Lehmann et al, 2000). In particular, PSi structures constituted of successive layers with different porosities, such as planar waveguides or multilayers, can be fabricated by controlled variation of the current density during anodization.…”

Section: Porous Silicon Anodizationmentioning

confidence: 99%