Thin Solid Films 459 (2004) 249–253 0040-6090/04/$ - see front matter  2003 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2003.12.103 Photoluminescence from photochemically etched highly resistive silicon T. Hadjersi *, N. Gabouze , N. Yamamoto , K. Sakamaki , H. Takai a, a b c c Unite de Developpement de la Technologie du Silicium (UDTS), 2, Bd. Frantz Fanon, B.P. 399 Alger-Gare, Alger, Algeria a ´ ´ Communications Research Laboratory, Basic and Advanced Research Division, 4-2-1, Nukui-kitamachi, Koganei, Tokyo 184-8795, Japan b Tokyo Denki University, Department of Electrical Engineering, 2-2 Kanda-Nishiki-cyo, Chiyoda-ku, Tokyo 101-8457, Japan c Available Online March 5 2004 Abstract The photochemical etching method has been performed on n-type Si(111) wafer with a resitivity of 4.2 kV cm, in a mixture of HF and H O , under He–Ne laser (633 nm) irradiation. The morphology of the porous films grown after exposure to a He– 22 Ne laser at normal incidence were analysed by scanning electron microscopy (SEM). The results show that the films obtained are porous. Furthermore, excitation of the porous silicon layer elaborated from highly resistive silicon samples under He–Cd laser (325 nm) irradiation shows that the porous films are photoluminescent. Photoluminescence of the porous samples was observed only for porosification times approximately or higher than 60 min. It is shown that the PL intensity peak decreases with increasing photochemical etching time. However, a slight shift (blue shift) of the PL peak wavelength is noticed as the etching time increased. In addition, the luminescence spectra are found to be similar to those reported recently for porous Si films produced on silicon of low resistivity. Finally, the quantum confinement effect has been invoked to explain the bright, visible, room temperature PL of PS.  2003 Elsevier B.V. All rights reserved. PACS: 81.05.Rm; 78.55.Mb; 68.37.Hk Keywords: Porous silicon; Photo-chemical etching; Photoluminescence; Quantum effects 1. Introduction Since the discovery of visible-luminescence from porous silicon (PS) in 1990 w1x, there has been a great interest in this material w2x. Porous silicon is usually prepared by anodisation of silicon in aqueous hydrogen fluoride (HF) w3,4x. However, for highly resistive crys- talline and amorphous silicon an instability of the electric field at the electrolyte ysilicon interface, which limits the maximum thickness (t ) of the nanoporous m layer can be observed w5x. In order to increase the t of m PS, several strategies may be considered: (i) varying the resistivity of the electrolyte w5x, (ii) illumination of the sample (injection of carriers) during the anodisation w6x, (iii) photochemicaletching w7x.Asthelatterstrategy has been much less studied and it is a simple method compared with anodisation, since it requires no elec- *Corresponding author. Tel.: q213-21-43-35-11; fax: q213-21- 43-35-11. E-mail address: hadjersi@yahoo.com (T. Hadjersi). trodes on the back surface of crystalline Si wafers, it has been used in this work to form the porous silicon layers on highly resistive silicon. Recently, Yamamoto etal.haveimprovedthismethodbyincludinganoxidant chemical species (HO ) in HF and proposed a new 22 method to form a luminescence layer on a medium doped n-type silicon w8x. In this paper, we report on the formation of visible- light-emitting layers on a highly resistive n-type silicon wafer by a photochemical etching method. We have discussed the etching time dependence on the morphol- ogy of porous silicon layers and on the luminescence characteristics as photoluminescence (PL) peakintensity and the peak wavelength of photochemically etched silicon. The changes in the PL spectrum are attributed to the structural modifications of porous silicon layers caused by etching. 2. Experimental A single-crystalline n-type Si wafer (111), having a resistivity of 4.2 k V cm has been used. The experi-