Quantum effects in silicon nanodots

Magdalena Lidia Ciurea

National Institute of Materials Physics, Bucharest-Magurele 77125, Romania

	In this work we have studied the quantum effects that appear in the electrical transport through systems formed by silicon nanodots embedded in an amorphous silicon dioxide matrix. The films were prepared by co-sputtering of silicon and silicon dioxide on rectangular quartz substrates [1]. After deposition, the samples were annealed at high temperature to produce the nucleation of silicon crystallites. This method gives a continuous variation of the nanocrystalline silicon (nc-Si) concentration along the slide. The mean size of the silicon nanodots is 5 nm [2]. Some of the nanodots are twinned (and even multitwinned). The crystallites tend to form chains. Parallel equidistant aluminum electrodes were deposited in coplanar configuration across the films.
	Current – voltage (I – V) [3] and current – temperature (I – T) [4] characteristics were measured. I – V curves are symmetric and present a superlinear character. I – T characteristics have several activation energies, depending on the nc-Si concentration and the applied bias.
	From I – V characteristics it results that the transport mechanism is the field-assisted tunneling under Coulomb blockade. The modeling of this effect leads to the evaluation of the mean width and number of the tunneled potential barriers, on the basis of the mean height of the barrier between nc-Si and SiO2, previously measured by us [5].
	The activation energies from the I – T curves were interpreted on the basis of a quantum confinement model. In this model, the nanodot is described as an infinite rectangular quantum well. The activation energies are then identified with differences between quantum confinement energies. The model also allows the evaluation of the mean diameter of the nanodots.
	The obtained results are in good agreement with the microstructure investigations [2].

	References

1.	M. Dovrat, Y. Oppenheim, J. Jedrzejewski, I. Balberg, and A. Sa'ar, Radiative versus non-radiative decay processes in silicon nanocrystals probed by time-resolved photoluminescence spectroscopy, Phys. Rev. B 69, 155311-1 – 155311-8, 2004.
2.	V. S. Teodorescu, M. L. Ciurea, V. Iancu, M. G. Blanchin, Microstructure of Si/SiO2 nanocomposite films, Proc. IEEE CN 04TH8748, Int. Semicond. Conf. CAS 2004, Sinaia, 3 – 6 octombrie 2004, 1, 59 – 62, 2004.
3.	V. Iancu, M. Draghici, L. Jdira, M. L. Ciurea, Conduction mechanisms in silicon-based nanocomposites, J.Optoelectron. Adv. Mater. 6 (1), 53-56, 2004.
4.	V. Iancu, L. Jdira, M. Draghici, M. R. Mitroi, I. Balberg, M. L. Ciurea, Electrical behavior of Si/SiO2 nanocomposite films, Proc. IEEE CN 03TH8676, Int. Semicond. Conf. CAS 2003, Sinaia, 3 – 6 octombrie 2003, 1, 83 – 86, 2003.
5.	M. L. Ciurea, V. Iancu, Electrical properties of nanocrystalline porous silicon, invited paper, Proc. IEEE CN 00TH8486, Int. Semicond. Conf. CAS 2000, Sinaia, 6 – 9 octombrie 2000, 1, 55 – 64, 2000.