Materials Science and Engineering B69 – 70 (2000) 345 – 349 Photo- and electroluminescence from nanocrystalline silicon single and multilayer structures P. Photopoulos a, *, A.G. Nassiopoulou a , D.N. Kouvatsos a , A. Travlos b a IMEL/NCSR ‘Demokritos’, P.O. Box 60228, 153 10 Aghia Paraskei Attikis, Athens, Greece b Institute of Materials Science, NCSR ‘Demokritos’, P.O. Box 60228, 153 10 Aghia Paraskei Attikis, Athens, Greece Abstract Single and multilayer structures of nanocrystalline silicon/silicon dioxide (nc-Si/SiO 2 ) were fabricated by alternate sequences of low-pressure chemical vapor deposition (LPCVD) of thin silicon layers and high temperature thermal oxidation. Silicon was deposited at 580°C and the obtained films were initially amorphous. During the high-temperature oxidation step, crystallization of the amorphous layer and simultaneous oxidation of the top layer was assured. The oxide thickness was controlled by controlling the oxidation time. Multilayers with five to ten periods were fabricated, with nc-Si thickness between 1.5 and 15 nm, and SiO 2 thickness between 5 and 10 nm. Photoluminescence (PL) and transmission electron microscopy (TEM) were used to characterize the films. Nanocrystalline silicon layers of thickness below 5 nm showed 10 to 15 times more intense PL than those from thicker layers (12 – 16 nm thick). Electroluminescence (EL) was also studied and results will be discussed. © 2000 Elsevier Science S.A. All rights reserved. Keywords: Photoluminescence; Electroluminescence; Nanocrystalline silicon single and multilayer structures www.elsevier.com/locate/mseb 1. Introduction Nanocrystalline silicon is currently studied for impor- tant new applications in nanoelectonic devices, includ- ing single electron transistors and memories, and silicon based light emitting structures for optoelectronics and displays. A key issue in all cases is to obtain nanocrys- tallites of well-controlled sizes and reduced size disper- sion in a matrix composed of a high dielectric constant material. Different deposition processes and host mate- rials were used by groups working in this field: Si and SiO 2 rf co-sputtering on bulk silicon [1], Si + implanta- tion into SiO 2 layers [2,3], low pressure chemical vapor deposition (LPCVD) [4], amorphous silicon deposition and recrystallization [5], etc. It was revealed that one of the best ways to control silicon nanocrystallite size was to limit the silicon layer thickness. Multiquantum wells of nc-Si and CaF 2 were obtained by molecular beam epitaxy (MBE) deposition at room temperature [6]. A great effort is however concentrated on the use of silicon dioxide as dielectric material, because of its full compatibility with silicon microelectronics and its well- known properties. Silicon superlattices within SiO 2 were first fabricated by Lockwood et al. [7], by molecular beam epitaxy and ultraviolet ozone treatment. The obtained silicon layers were amorphous. Tsybeskov et al. [5] succeeded in recrystallizing Si/SiO 2 superlattices deposited by sput- tering or LPCVD and to obtain silicon nanocrystallites within an amorphous phase. The size distribution was, however, not well controlled and poor photolumines- cence (PL) properties were obtained from those structures. In an attempt to better understand PL from silicon nanocrystallites and to improve light emission by con- trolling size dispersion and nanocrystallite surface pas- sivation, single and multilayer structures of silicon and SiO 2 of varying thicknesses were fabricated in this work and PL and electroluminescence (EL) emissions were systematically studied. The silicon layer thickness was monitored by controlling the duration of high tempera- ture thermal oxidation of the layers initially deposited by LPCVD. PL with a narrower spectral distribution and much higher intensity was obtained from silicon layers of thickness below 2 nm compared to thicker layers. The obtained results will be discussed in detail below. * Corresponding author. 0921-5107/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved. PII:S0921-5107(99)00402-X