EFM Study on Ge Island: Carrier Charge and Storage Effect
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EFM Study on Ge Island: Carrier Charge and Storage Effect Zhen Lin1, Pavel Brunkov2, Xueying Ma1, Franck Bassani3, Georges Bremond1 1 Institut des Nanotechnologies de Lyon, UMR 5270 Université de Lyon, Institut National des Sciences Appliquées, INSA Lyon, Bât. Blaise Pascal, 20, avenue Albert Einstein - 69621 Villeurbanne Cedex, France; 2 Ioffe Physical-Technical Institute of the Russian Academy of Sciences, Saint-Pétersbourg, 194021, Russia 3 Institut Matériaux Microélectronique Nanosciences de Provence, UMR CNRS 6242, Avenue Escadrille Normandie-Niemen - Case 142, F-13397 Marseille Cedex 20, France ABSTRACT In this letter, individual Ge nano island on top of a silicon dioxide layer of thermally grown on a n+ type doped silicon (001) substrate have been studied. The charging ability of an individual Ge island was evaluated by EFM two-pass lift mode measurement. Such Ge nano island becomes an iso-potential and behaves as a conductive material after being charged. These charges were directly injected and were trapped homogenous in the isolated Ge island. It is also shown that the dominant charge decay mechanism during discharging of nc-Ge is related to the leakage of these trapped charges. Further more, the retention time of these trapped charges was evaluated and the electrostatic force was also studied by using different tip bias during scan. Such a study should be very useful to the Ge-nc in memory applications. INTRODUCTION Nowadays, the semiconductor technology is facing a great challenge to increase the device performance while reducing its dimension. This downscaling in microelectronics industry causes a drastic development of microscopy to reveal new physical characteristics at nanometer scale such as Coulomb blockade1-3, quantized charging effects4-7 and single electron transfers8-13. Atomic force microscopy (AFM) 14 is becoming a powerful tool for nanometer scale measurement. It can provide simultaneous topography and various physical feature images with some additional applications such as SCM, EFM, TUNA, KPFM. Electrostatics force microscopy (EFM) is used specially for characterizing materials for accurate local and nondestructive electrical properties for a wide range of characterisations such as surface potential, charge distributions15-16, doping concentration17 and dielectric constant18. EFM is also able to easily and non-destructively inject and detect the localised charge in nanostructures, on or below the surface by a special two-pass LiftMode. This ability has been used to study the distribution of trapped charge in various types of nano dot samples19-21. Currently, characterisation of the electronic devices which are composed of individual Germanium nano islands was few studied by EFM at room temperature. However, such nanostructures are of a great interest because the injected charge carriers are constrained in their propagation, and interact in a finite geometry. THEORY The Ge nano islands have been fabricated on a very thin wafer. A 15nm thick Ge layer was deposited over the 5nm s
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