ELSEVIER Thin SolidFilms276 (1996) 171-174 Strong 1.54 luminescence from erbium-doped porous silicon A. Dorofeev a, E. Bachilo ", V. Bondarenko a, N. Gaponenko a, N. Kazuchits a, A. Leshok a, G. Troyanova ", N. Vorozov ~, V. Borisenko a, H. Gnaser b, W. Bock b, p. Becker b, H. Oechsner b a Belarusian State University ofinformatics and Radioelectronics, P. Browka 6. 220027 Minsk, Belarus b Institutfiir Oberfliichen- und Schichanalytik, Universitiit Kaiserslautern, D-67663 Kaiserslautern, Germany Abstract Porous silicon doped by erbium electrodeposition or from spin-on silica gel film followed by rapid thermal processing at 950 °C or higher exhibited liquid-nitrogen and room-temperature luminescence at 1.54 ~m. The full width at half maximum was about 0.01 eV at 77 K. The mechanism of light emission from erbium-doped porous silicon is proposed. The direct bandgap of nanocrystallites in porous silicon is considered to provide an effective pumping media. Keywords: Luminescence; Erbium;Depositionprocess; Electrochemistry 1. Introduction Erbium-doped semiconductors are of interest due to their potential applications in optoelectronic devices operating at 1.54 I~m [!,2]. This wavelength is of great optoelectronic potential since it happens to coincide with that of the mini- mum for optical adsorption in silica-based glass fibers. Room- temperature photo- and eleetroluminescence at 1.54 I~m have been reported in erbium-doped GaP [3], GaAs [4], and InP [ 5 ] Erbium-doped Si [ 6-10] is particularly promising due to the possibility of integration of electronic and optical devices. Usually erbium-doped Si structures are created by high- energy (up to 5 MeV) ion implantation followed by high- temperature annealing. This method, however, is rather expensive and requires a long implant time. Porous silicon layers formed by electrochemical anodiza- tion of Si are shown to have a highly developed specific area which provides the high level of chemical activity and oxygen content in this material [ 11,12]. Previous studies of Au, Cu, and As [ 13,14] diffusion in porou~ silicon under rapid ther- mal processing demonstrated rather deep penetration of the impurities into the porous material. Besides, recently porous silicon was shown to exhibit effective photo- and electrolu- minescence in the visible range [15-18]. So, the unique combination of properties proves porous silicon to be a very promising material for optoelectronic applications. 0040-6090/96!$15.00 © 1996ElsevierScienceS.A. All nghts reserved SSD! 0040-6090 ( 95 ) 08082- i Recent studies have shown that porous silicon can be easily doped with erbium from spin-on films [19] or by electro- chemical erbium deposition followed by high-temperature annealing [ 20,21 ]. The highly porous structure provides suit- able conditions for fast surface diffusion of atoms into porous layers. Characterization of the photoluminescence of porous sili- con doped by electrochemical deposition of erbium and from spin-on films are presented and discussed in this paper. A phenomenological model of erbium-based luminescence of porous silicon is proposed. 2. Experimental P-type boron-doped Si (i11) wafers (0.3 [l cm and 10 [l cm) and Si (100) wafers ( 12 [l cm) were used as initial substrates. Uniform 5 p,m thick porous silicon layers were formed by anodization of the wafers in 40% is,~-propanol HF at anodic current densities J = 2-40 mA cm- ::. Half of each sample was mechanically masked during anodization to have virgin monocrystalline silicon for reference. Then the sam- ples were rinsed in de-ionized water for 15 rain and dried in a nitrogen atmosphere at room temperature. After preparation one part of the porous silicon samples was subjected to cathodic deposition of erbium at a current density J=0.125 mA cm -2 for 30 min [21 ]. Another part of experimental samples was covered with erbium-containing