IOP PUBLISHING NANOTECHNOLOGY Nanotechnology 21 (2010) 065706 (6pp) doi:10.1088/0957-4484/21/6/065706 Conductive AFM microscopy study of the carrier transport and storage in Ge nanocrystals grown by dewetting K Gacem 1 , A El Hdiy 1 , M Troyon 1 , I Berbezier 2 and A Ronda 2 1 Laboratoire de Microscopies et d’Etude de Nanostructures (EA 3799), Bˆ atiment 6, case no 15, UFR Sciences, Universit´ e de Reims Champagne Ardenne, F-51687 Reims Cedex 2, France 2 IN2MP CNRS UMR 6137, Facult´ e des Sciences et Techniques de Saint J´ erˆ ome, avenue Escadrille Normandie Niemen, Case 142, F-13397 Marseille Cedex 20, France E-mail: abdelillah.elhdiy@univ-reims.fr Received 24 August 2009, in final form 7 December 2009 Published 8 January 2010 Online at stacks.iop.org/Nano/21/065706 Abstract A combined conductive atomic force microscope (C-AFM)/scanning electron microscope (SEM) has been used to study the electric transport and retention mechanisms through Ge nanocrystals (NCs). The NCs were formed by a two-step dewetting/nucleation process on a silicon oxide layer grown on n-doped 〈001〉 silicon substrate. Without preliminary e-beam irradiation, electric images are obtained only with bias voltages larger than 8 V. This is due to the barrier height introduced by the presence of the native oxide on NCs and of the oxide layer on which the NCs are grown. After acquisition of an e-beam-induced current image, electric images (e-beam off) can be easily obtained at low bias voltages because of the trap creation in the oxide layer. We show that the critical threshold voltage to detect a current through the NCs decreases with NCs size. The band diagram of the contact in the presence of a p-doped diamond coated tip shows that the conduction mechanism is dominated by holes. At last we show a good memory effect with charge/discharge in the NCs resulting in a long retention time. (Some figures in this article are in colour only in the electronic version) 1. Introduction Semiconductor nanocrystals (NCs) or quantum dot (QDs)- based electronic and optoelectronic devices have attracted a great deal of attention thanks to their potential applications in the future memory market. Their specific properties have been widely studied [1, 2]. For instance, in memory devices, the use of charge trapping in nanometer-sized structures not only helps in reducing the charge quantity necessary to represent a bit, but may also contribute to enhance nonvolatility. An important advance in nonvolatile memory devices is the substitution of the metal or polycrystalline silicon floating gate by nanoparticle arrays. Thanks to its high resolution, the conductive atomic force microscopy (C-AFM) is a powerful technique for characterization of NCs and QDs as reported in previous studies [3–7]. One of the main points that comes out from these studies is that the conductance of the QDs is found to be larger than that of the InAs wetting layer in the case of InAs QDs grown on GaAs [3, 4] or InP [6, 7], and also larger than that of the substrate in the case of Ge QDs grown on Si substrate [5]. It has also been shown in a recent paper [7] that the electric transport mechanism through InAs/GaAs QDs depends on the kind of C-AFM probe used. The aim of this work is to study the local conduction of Ge nanocrystals grown by a two-step dewetting/nucleation process, and to explore the carrier charging/discharging effect. The study is performed with an atomic force microscope (AFM) working inside a scanning electron microscope (SEM). The latter serves to irradiate the specimen by the electron beam (e-beam) to acquire an e-beam induced current image and hence to facilitate the conduction current measurements. Indeed, a preliminary electron irradiation provides charge trapping in the oxide layers and in the NCs which is necessary to measure a current at reasonable bias voltages. Through this study, we determine the type of carriers involved in the electrical transport and the trapping/emission process between 0957-4484/10/065706+06$30.00 © 2010 IOP Publishing Ltd Printed in the UK 1