Borowik, L., Kusiaku, K., Deresmes, D., Théron, D., Diesinger, H., Melin, Thierry, Nguyen-Tran, T., Roca I Cabarrocas, Pere, Institut d’Électronique, de Microélectronique et de Nanotechnologie - UMR 8520 (IEMN), Centrale Lille-Institut supérieur de l'électronique et du numérique (ISEN)-Université de Valenciennes et du Hainaut-Cambrésis (UVHC)-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Université Polytechnique Hauts-de-France (UPHF), Laboratoire de physique des interfaces et des couches minces [Palaiseau] (LPICM), and École polytechnique (X)-Centre National de la Recherche Scientifique (CNRS)
International audience; The introduction of impurities in semiconductor nanocrystals is of fundamental interest to control their optical, electrical and magnetic properties[1]. Doping is essential to basically enhance electrical conductivity, and to build functional devices. This issue becomes of prime interest at the nanoscale for e.g. self-assembled devices based on organic, molecular or inorganic nanostructures, for which the control of doping can be either technologically difficult during the synthesis, and strongly depend on the environment, as in the case of carbon nanotubes[2] or physically limited, as in the case of silicon nanowires for which internal doping becomes unefficient due to dielectric screening[3].In this presentation, we investigate using ultra-high vacuum non-contact atomic force microscopy and Kelvin probe force microscopy (KFM) the possibility of using doped nanocrystals as electron sources to perform external remote doping of nanostructures and nanodevices. The focus is here to study the mechanisms of charge transfer from nanocrystals at the scale of the individual nanocrystals. To do so, we study the charge transfer from hydrogen-passivated phosphorus-doped[4] silicon nanocrystals towards silicon substrates by means of amplitude-modulation KFM. From the measurement of the electrostatic potential of ionized nanocrystals, we demonstrate that the nanocrystal doping (i) provides an internal passivation of the nanocrystal surface states and (ii) induces a charge transfer following an energy compensation mechanism similar to remote doping, but strongly enhanced by quantum confinement. Results provide a direct measurement of the nanocrystal band-gap opening induced by quantum confinement in the 2-50nm range[5], in agreement with parametrized tight-binding calculations. They also put forward the possibility of using doped nanocrystals to achieve controlled external remote doping of nanostructures and nanodevices, with expected two-dimensional charge densities in the range of 10^11-10^14 cm-2, or linear charge densities in the range of 10^5-10^7 cm-1.References: [1] For a recent review, see: D.J. Norris, A. L. Efros, S. C. Erwin, Science 319,776-1779 (2008) ; S. C. Erwin, L. Zu, M. I. Haftel, A. L. Efros, T. A. Kennedy, and D. J. Norris, Nature 36,91 (2005).; D. Yu, C.J. Wang, and P. Guyot-Sionnest, Science 300, 1277 (2003).[2] V. Derycke, R. Martel, J. Appenzeller, and Ph. Avouris, Appl. Phys. Lett. 80, 2773 (2002).[3] M. T. Bjork, H. Schmid, J. Knoch, H. Riel, W. Riess, Nature Nanotechnology 4, 103-107 (2009); M. Diarra, Y. M. Niquet, C. Delerue, and G. Allan, Phys. Rev. B 75, 045301 (2007).[4] A. R. Stegner, R. N. Pereira, K. Klein, R. Lechner, R. Dietmueller, M. S. Brandt, M. Stutzmann and H. Wiggers, Phys. Rev. Lett. 100, 026803 (2008).[5] L. Borowik, K. Kusiaku, D. Théron, D. Deresmes, H. Diesinger, T. Mélin, T. Nguyen-Tran, P. Roca i Cabarrocas (submitted to Phys. Rev. Lett.)