X-ray diffraction study of the morphology and structure of pulse-anodized porous Si multilayers
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TION AND SCATTERING OF IONIZING RADIATIONS
X-Ray Diffraction Study of the Morphology and Structure of Pulse-Anodized Porous Si Multilayers A. A. Lomova, V. A. Karavanskiœb, A. L. Vasil’eva, and D. V. Novikovc a
Shubnikov Institute of Crystallography, Russian Academy of Sciences, Leninskiœ pr. 59, Moscow, 119333 Russia e-mail: [email protected] b General Physics Institute, Russian Academy of Sciences, ul. Vavilova 38, Moscow, 119991 Russia c Deutsches Electronen Synchrotron DESY, Notkestr. 85, D-22607, Hamburg, Germany Received December 21, 2007
Abstract—Porous Si layers, obtained by pulsed electrochemical etching of n-Si(001) substrates (resistivity 0.01 Ω cm) in a 1 : 1 mixture of hydrofluoric acid and ethanol, have been investigated by high-resolution X-ray diffraction and electron microscopy. The average structural parameters of the layers grown (thickness, strain, porosity, pore size) are determined. It is found that pulsed anodic oxidation leads to a decrease in the average strain of layers. It is established that, at frequencies up to 1 Hz, anodic oxidation makes obtaining porous silicon multilayers with layer thicknesses of 20–300 nm containing Si nanocrystallites possible. It is shown that X-ray diffuse scattering from pores yields information about their ordering and can be used to monitor the processes of electrochemical etching used to form porous layers. PACS numbers: 61.10.Nz, 61.10.-i DOI: 10.1134/S1063774508050039
INTRODUCTION The electrochemical etching of semiconductor substrates has been used for a long time to create porous materials with new properties [1, 2]. This method is most widespread for silicon. In the last decade, micro-, mesa-, and nanoporous silicon has been intensively studied in view of the large variety of its properties and applications [3]. For example, visible photoluminescence at room temperature was observed in nanoporous silicon layers obtained by anodic oxidation. Although the physical nature of this effect is still discussed, anodic etching has been actively applied once the possibilities of this process for obtaining crystallites with quantum-size effects were demonstrated. It was found that the degree of porosity, thickness, and strain of layers, as well as the morphological parameters of pores and crystallites (form, sizes, orientation), can easily be controlled by changing the anode current [4–7]. In some cases, modern technology needs ordered locally inhomogeneous structures. It was shown in [8–10] that self-regulating pores with a correlation length exceeding the distance between pores can be obtained. In particular, modulation of the current density made it possible to obtain superlattices with nanoporous layers [6] and optical Bragg structures [11, 12]. Layers with an ordered arrangement of pores in the lateral direction can be obtained using photolithography; however, a specific feature of electrochemical etching is the possibility of easily creating layers with areas of several tens of square centimeters [13].
Preparing nanoporous silicon by anodization de
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