arXiv subjects

Bruno Pellegrini

Publications and source records attributed to Bruno Pellegrini.

3 recordsLinked to original sources

arXiv2013

1/f noise in graphene

We present a novel and comprehensive model of 1/f noise in nanoscale graphene devices that accounts for the unusual and so far unexplained experimental characteristics. We find that the noise power spectral density versus carrier concentration of single-layer sheet devices has a behavior characterized by a shape going from the M to the Gamma type as the material inhomogeneity increases, whereas the shape becomes of V type in bilayer sheet devices for any inhomogeneity, or of M type at high carrier concentration. In single-layer nanoribbons, instead, the ratio of noise to resistance versus the latter quantity is approximately constant, whereas in the bilayer case it exhibits a linear decrease on a logarithmic scale as resistance increases and its limit for zero resistance equals the single-layer value. Noise at the Dirac point is much greater in single-layer than in bilayer devices and it increases with temperature. The origin of 1/f noise is attributed to the traps in the device and to their relaxation time dispersion. The coupling of trap charge fluctuations with the electrode current is computed according to the electrokinematics theorem, by taking into account their opposite effects on electrons and holes as well as the device inhomogeneities. The results agree well with experiments.

cond-mat.mes-hall↗

arXiv1995

A compact formula for the density of states in a quantum well

In this paper we derive a formula for the density of states in the presence of inelastic scattering in the quantum well of a double barrier structure as a function of a characteristic time of the motion of electrons (namely, the round trip time in the well) and of transmission probabilities for the whole structure and for each barrier. In the model we use the scattering processes due to phonons, impurities, and interface roughness, are taken into account by a unique fenomenological parameter, the mean free path, which plays the role of a relaxation length. We also show that, for lower rates of incoherent processes, the derived formula reduces to the one obtained by means of the Breit-Wigner formalism.

cond-mat↗

arXiv1995

A unified approach to electron transport in double barrier structures

In this paper we show an approach to electron transport in double barrier structures which unifies the well known sequential and resonant tunneling models in the widest range of transport regimes, from completely coherent to completely incoherent. In doing so, we make a clear distinction between ``approaches'' and ``transport regimes,'' in order to clarify some ambiguities in the concept of sequential tunneling. Scattering processes in the well are accounted for by means of an effective mean free path, which plays the role of a relaxation length. Our approach is based on a recently derived formula for the density of states in a quantum well, as a function of the round trip time in the well and of trasmission and reflection probabilities for the whole structure and for each barrier.

cond-mat↗