The Quantitative Study of Trapped Charges in Nano-Scale Ge Island by EFM Measurement
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1250-G06-12
The Quantitative Study of Trapped Charges in Nano-Scale Ge Island by EFM Measurement Zhen Lin1, Pavel Brunkov2, Franck Bassani3, Georges Bremond1 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 1
ABSTRACT In this work, an individual Ge island on top of silicon dioxide layer has been charged by a conductive EFM tip and quantitatively characterized at room temperature. Electrons or holes were successfully injected and were trapped homogenously in the isolated nano-scale Ge island. In order to quantitatively study these trapped charges, a truncated capacitor model was used to approximate the real capacitance between the tip and island surface. The analytical expression of the quantity of trapped charges in isolated Ge island as a function of the EFM phase signal was deduced. Applying a tip bias for -7V during 30 seconds leads to an injection about 800 electrons inside an individual Ge island. INTRODUCTION Injection and detection of localized charges in nanostructures, on or below the surface, are the key issues in the field of nanoelectronics. Electrostatic force microscopy (EFM) is proved to be one of the most efficient tools not only for atomic scale characterisation of surfaces1-2 but also for local surface modification and structuring in sub-micrometre and nanometre ranges3-5. Using a conductive tip, it is possible to electrically bias the oscillating tip with respect to the sample and characterize materials for accurate local and non-destructive electrical properties for a wide range of characterisations such as surface potential, charge distribution, doping concentration and dielectric constant6-9. It is also possible to use the twopass lift mode to minimize the influence of morphology over the sample surface by keeping the long range electrostatic force distance constant. This ability has been used to quantitatively study of the charge injection and retention in some kind of samples10-12 such as Germanium nano islands deposited directly on oxide layer for non-volatile memory application at room temperature. However, a quantitatively study of these trapped charges inside the isolated nano-scale Ge island is of great importance for the memory applications and is required. EXPERIMENT DETAILS These nano-scale Ge islands have been fabricated on a very thin wafer. A 15nm thickness Ge layer was deposited over the 5nm SiO2 in ambient temperature and was thermal annealed by 750°C for 20 minutes. The Ge nano crystals were formed with an average diameter around 150nm. It is about 7 times the thickness of the Ge layer24. Over the dots there is a natural oxide layer about only 2 nm so that the
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