Injection et détection de charges dans des nanostructures semiconductrices par Microscopie à Force Atomique

Président du jury: M. Hans Hug (Université de Bâle, Suisse) Rapporteurs: M. Jean-Marc Triscone (Université de Genève) et M. Thierry Melin (IEMN Lille) Examinateur: Herve Courtois (CNRS Grenoble)Isolated semiconducting nanostructures have the property to confine charges on long time scales. The charge retention depends on several parameters such as the size of the nanostructure, the density and the quality of the interface with the dielectric. We have investigated these properties with an AFM in air with electrostatic force microscopy (EFM). EFM allows injecting charges locally and then probing, with a sensitivity of a few tens of electrons, the individual as well as collective behaviors of nanostructures. We have characterized the non-linear tip-sample interaction for an electrostatic coupling. We then studied the behavior of Si and Ge nanostructures on SiO2. The saturation of the electron cloud for a network of nanocrystals was evidenced, while kinetic roughening of the electron cloud in a dense network of nanocrystals was observed.Les nanostructures semiconductrices isolées possèdent la propriété de confiner les charges sur des temps longs. La rétention de charges dépend de plusieurs paramètres tels que la taille de la nanostructure, la densité et la qualité de l'interface avec le diélectrique. Nous avons exploré ces propriétés à l'aide d'un AFM à l'air par microscopie à force électrostatique (EFM). L'EFM permet d'injecter des charges localement puis de sonder avec une sensibilité de quelques dizaine d'électrons seulement les comportements individuel aussi bien que collectif des nanostructures. Nous avons caractérisé l'interaction pointe-surface non-linéaire pour un couplage électrostatique, puis avons étudié le comportement de nanostructures de Si ou Ge déposées sur du SiO2. Nous avons mis en évidence d'une part la saturation du nuage de charge dans un nappe de nanocristaux, et d'autre part la propagation inhomogène de la charge à l'échelle de l'heure dans une nappe de nanocristaux plus dense

Injection et détection de charges dans des nanostructures semiconductrices par Microscopie à Force Atomique

Président du jury: M. Hans Hug (Université de Bâle, Suisse) Rapporteurs: M. Jean-Marc Triscone (Université de Genève) et M. Thierry Melin (IEMN Lille) Examinateur: Herve Courtois (CNRS Grenoble)Isolated semiconducting nanostructures have the property to confine charges on long time scales. The charge retention depends on several parameters such as the size of the nanostructure, the density and the quality of the interface with the dielectric. We have investigated these properties with an AFM in air with electrostatic force microscopy (EFM). EFM allows injecting charges locally and then probing, with a sensitivity of a few tens of electrons, the individual as well as collective behaviors of nanostructures. We have characterized the non-linear tip-sample interaction for an electrostatic coupling. We then studied the behavior of Si and Ge nanostructures on SiO2. The saturation of the electron cloud for a network of nanocrystals was evidenced, while kinetic roughening of the electron cloud in a dense network of nanocrystals was observed.Les nanostructures semiconductrices isolées possèdent la propriété de confiner les charges sur des temps longs. La rétention de charges dépend de plusieurs paramètres tels que la taille de la nanostructure, la densité et la qualité de l'interface avec le diélectrique. Nous avons exploré ces propriétés à l'aide d'un AFM à l'air par microscopie à force électrostatique (EFM). L'EFM permet d'injecter des charges localement puis de sonder avec une sensibilité de quelques dizaine d'électrons seulement les comportements individuel aussi bien que collectif des nanostructures. Nous avons caractérisé l'interaction pointe-surface non-linéaire pour un couplage électrostatique, puis avons étudié le comportement de nanostructures de Si ou Ge déposées sur du SiO2. Nous avons mis en évidence d'une part la saturation du nuage de charge dans un nappe de nanocristaux, et d'autre part la propagation inhomogène de la charge à l'échelle de l'heure dans une nappe de nanocristaux plus dense

Injection and detection of electrical charges by EFM

Electrostatic Force Microscopy and electric charges in semiconducting nanostructure

Charging dynamics and strong localization of a two-dimensional electron cloud

The dynamics of charge injection in silicon nanocrystals embedded in a silicon dioxide matrix is studied using electrostatic force microscopy. We show that the presence of silicon-nanocrystals with a density of 1011 cm2 is essential for strong localization of charges, and results in exceptional charge retention properties compared to nanocrystal-free SiO2 samples. In both systems, a logarithmic dependence of the diameter of the charged area on the injection time is observed on a time scale between 0.1 and 10 s (voltage ≤ 10 V). A field-emission injection, limited by Coulomb blockade, and a lateral charge spreading due to a repulsive radial electric field are used to model this logarithmic behavior. Once the tip is retracted, the electron cloud is strongly confined in the nanocrystals and remains completely static

Characterisation of trapped electric charge carriers behaviour at nanometer scale by electrostatic force microscopy

International audienceAtomic force microscopy (AFM) and related electrical probe techniques such as electrostatic force microscopy (EFM) can be used to perform injection and detection of electric charge carriers in nanostructures or oxide layer at the nanometer scale. In this paper the control and the deposition of both positive and negative local charges are described and discussed. A basic introduction to both the theoretical and experimental techniques of EFM is also presented. In addition a review of the analytical calculation of tip-surface capacitance interaction is described and then utilised to estimate charge storage in oxide layers and nanostructures from EFM images or spectroscopy curves. The charge resolution of EFM at room temperature and a controlled atmosphere is estimated to be about 20 charge carriers. The EFM technique is also used to inject charges and to study their behaviour in confined silicon nanostructures covered by a thin layer of oxide and separated from the Si substrate by a SiO2 layer. The total injected charge is found to depend on the thickness of the oxide layer. The electric field has emerged to be a key parameter in the injection mechanism. The dynamics and propagation of the deposited charge carriers have been studied and a homogenous distribution of the charge in the nanostructure has been observed. Thanks to these studies and observation, the localisation of the trapped charges has been determined: it occurs mainly in the silicon pattern rather than on the thin covering oxide layer. This charge localisation together with charge energy calculation leads to a better understanding of the origin of the charge dissipation