book of abstracts - IM2NP

A B S T R A C T S TUESDAY, JUNE 29 N A N O S E A 2 0 1 0
Room Port-Pin
8H30-9h10
Electrical, optical and structural properties of self-organized Ge nanocrystals.
N.L. Rowell1, D.J. Lockwood1, I. Berbezier2, G. Amiard2, L. Favre1, M.
Aouassa2,4, A. Ronda2, K. Gacem3, A. El Hdyi3, M. Troyon3, M. Scarselli4, P.
Castrucci4, M. De Crescenzi4, H. Maaref5 (1 National Research Council of Canada, 1200 Montreal
Road, Ottawa, ON K1A 0R6, Canada; 2IM2NP, CNRS – Univ. Aix Marseille, Campus St. Jérôme, Case 142, 13397
Marseille CEDEX 20, France ; 3LMEN, Case 15, UFR Sciences, Université de Reims, Champagne-Ardenne, 51687
Reims Cedex 2, France ; 4 Univ. Di Roma 2 Tor Vergata, Via della Ricerca Scientifica , Roma, Italy Uni Tor
Vergata; 5 LPSCE, Faculté des Sciences de Monastir, Uni. Monastir, Avenue de l'environnement 5019 Monastir,
Tunisia) Nelson.Rowell@nrc-cnrc.gc.ca
1 – Introduction
During the last decade, significant progress has been made towards the development of new processes for
integrating nanostructured materials into novel micro- and opto-electronic devices. The nanostructures of
interest include arrays of clusters, nanoparticles, quantum dots and wires. For most of the potential
applications the nanostructures must be ordered and highly homogeneous in size in order to exploit the
quantum effects for device applications. Recently notable advances have been made in dot self-assembly and
in our understanding of their physical properties [1].
2 – Abstract
Achieving high densities of self-organized Ge quantum dots directly on Si surfaces remains problematic.
The normal growth mechanism - Ge clustering from a Ge wetting layer - places constraints on the dot size,
density, and distribution limiting the best-case dot density to between 109 and 1010 cm−2. At the same time,
the quality of the dots is compromised by interdiffusion that leads to GeSi alloying at dot interfaces.
However for SiO2 substrates, Ge islanding, since it is driven by a dewetting process (surface diffusion and
equilibrium surface morphology), occurs without forming a wetting layer. Therefore a much larger dot
density [2] is possible and dot patterning can be achieved [3-5] with such a substrate. For example, in [5],
crystalline Ge dots with an average size of 5 nm and a density of 3×1012 cm−2 were obtained that displayed
the onset of (001) and (113) faceting and a low aspect ratio. Such morphology is attributed to the
thermodynamically limited, equilibrium shape of Ge in this system.
We will discuss the influence of size on the structural, electrical and optical properties of Ge dots. We
demonstrate using transmission electron microscopy that Ge dots exhibit a pseudo-equilibrium shape
independent of annealing conditions. The bandgap of individual dots determined by scanning tunnelling
spectroscopy is directly related to their size as predicted by quantum confinement [2,6]. This is confirmed by
optical characterization of Ge dots embedded in an amorphous Si matrix [7,8]. In addition, C-V and I-V
characteristics were attributed to electron (hole) injection/emission in the Ge dots, which display good
memory effects with long storage times [9,10].
3 – Conclusion
Using a combination of structural, optical and electronic characterization techniques, we have demonstrated
novel properties that can be attributed to quantum confinement effects resulting from the ultra-small size of
Ge dots.
[1] I. Berbezier, A. Ronda, Surf. Sci. Rep. 64, 47 (2009).
[2] I. Berbezier, A. Karmous, A. Ronda, A. Sgarlata, A. Balzarotti, P. Castrucci, M. Scarselli, M. De Crescenzi, Appl. Phys. Lett. 89, 063122 (2006).
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