Single electron charging effect in individual Si nanocrystals
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Single electron charging effect in individual Si nanocrystals. P. Gentile1, T. Baron2*, N. Magnea1, P. Mur3, F. Martin3, M.N. Séméria3. 1
Département de Recherche Fondamentale, CEA-Grenoble, 17 rue des Martyrs, 38054 Grenoble Cedex 9, France. 2 Laboratoire de Physique de la Matière, CNRS-INSA Lyon, 20 avenue Albert Einstein, 69621 Villeurbanne Cedex, France. 3 Leti- CEA Technologie Avancées, 17 rue des Martyrs, 38054 Grenoble Cedex 9, France. ABSTRACT We present a detailed study of the electronics properties of individual silicon nanocrystals (nc-Si) elaborated by Low Pressure Chemical Vapor Deposition on 1.2 nm thick SiO2 grown on Si (100). The combination of ultra thin oxide layers and highly doped substrates allows imaging the hemispherical dots by Scanning Tunneling Microscopy. By analyzing the STM images, we deduce a size distribution, which ranges between 3 and 6 nm with a surface density around 1012 cm-2. Spectroscopic studies of single dots are made by recording the I(V) curves on the Si nanocrystal accurately selected with the metallic tip. These I(V) curves obtain on a single dot, exhibit Coulomb blockade and resonant tunneling effects. Coulomb pseudo gaps, Ec, between 0.15 and 0.2 V are measured for different dots. From the width and height of the staircases observed at bias greater than Ec, 60 meV and 40 pA respectively, capacitance of 0.5 to 1 aF and tunnel resistance of 3.5x108 and 5.7x109 Ohms are measured within the orthodox approximation for asymmetric junctions. We have determined, from experimental measurements, the energy of the first level confined in nc-Si. INTRODUCTION Silicon quantum dots have been used to fabricate devices, which exhibit single electron effects even at room temperature [1]. In fact, the nanometer size of the dots allows to obtain a small total capacitance of the island to its environment. The single electron charging energy e2/2C exceeds then the thermal energy kT, and the resistance of the tunnel junction, made of silicon dioxide, is larger than the quantum resistance. These single electron tunneling effects, namely Coulomb gap and Coulomb staircase, were clearly observed in a transistor utilizing Si selfassembled quantum dots [2]. However, the properties of individual Silicon island have not been reported so far. Most of the studies on individuals island are realized by using a Scanning Tunneling Microscope (STM) [*]. Indeed, by this way two serial coupled junctions can be realized. The advantages of such an experiment are (i) small capacitances can be obtained and (ii) individual island with different and defined size can be probe. By this means, Coulomb effect was observed on small metallic island on a thin oxide layer deposited on a metallic substrate [3]. In this paper, we focus our attention on the nanocrystals Silicon nc-Si/SiO2 system that seems to be a good candidate for future devices and memories integrating quantum dots and single electron effects. Here we report on electrical properties of individual silicon quantum dots using a STM. EXPERIMENTAL DETAILS The S
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