J. Phys. I France
Volume 4, Numéro 8, August 1994
Page(s) 1181 - 1197
DOI: 10.1051/jp1:1994248
J. Phys. I France 4 (1994) 1181-1197

Nanostructural and nanochemical investigation of luminescent photoelectrochemically etched porous n-type silicon

A. Albu-Yaron1, S. Bastide1, D. Bouchet2, N. Brun2, C. Colliex2 and C. Lévy-Clément1

1  Laboratoire de Physique des Solides de Bellevue, 1 place Aristide Briand, 92195 Meudon, France
2  Laboratoire de Physique des Solides, Bât. 510, Université Paris-Sud, 91405 Orsay, France

(Received 2 February 1994, accepted in final form 2 May 1994)

Porous silicon obtained on n-type silicon by photoelectrochemical etching in HF, is formed of a macroporous silicon layer beneath a nanoporous silicon layer. Microstructural investigations and chemical analysis at the atomic level of the nanoporous silicon film (obtained from a highly doped (111) oriented Si substrate) have been done by high resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS) using a scanning transmission electron microscope (STEM). We have found chat the nanoporous Si consists of a regular Si macroarray with triangular geometry. Nanometer-size tangled wires are contained within and attached to the macroarray. HRTEM images clearly demonstrate the existence of quantum-sized Si wires made of a crystalline core covered with an amorphous layer. Electron energy loss spectra (EELS) have been recorded for different positions of the incident probe across the quantum-sized Si wires. The results obtained in the low-loss region and at the Si L 23 edge have been compared with those recorded on reference specimens (Si/SiO 2 interface and hydrogenated Si sample). Although they do not exclude the presence of one or a few monolayers of foreign species, of hydrogen in particular, on the outer surface, our results generally support the quantumconfinement model to interpret the observed photoluminescence in nanoporous Si.

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