We show that shot noise in a resonant-tunneling diode biased in the negative differential resistance regions of the I-V characteristic is enhanced with respect to "full" shot noise. We provide experimental results showing a Fano factor of up to 6.6, and show that it is a dramatic effect caused by electronelectron interaction through the Coulomb force, enhanced by the particular shape of the density of states in the well. We also present numerical results from the proposed theory, which are in agreement with the experiment, demonstrating that the model accounts for physics relevant to the phenomenon.[S0031-9007(97)05143-0] PACS numbers: 73.40.Gk, 72.70. + m, 73.20.Dx Deviations from the purely poissonian shot noise (the so-called "full" shot noise) in mesoscopic devices and resonant tunneling structures have been the subject of growing interest in the last decade [1][2][3][4][5][6][7][8][9][10][11]. The main reason is that noise is a very sensitive probe of electron-electron interaction [12], because of both the Pauli principle and the Coulomb force, and provides information but obtainable from dc and ac characterization; furthermore, noise depends strongly on the details of device structure, so that the capability of modeling it in nanoscale devices implies and requires a deep understanding of the collective transport mechanisms of electrons.Almost all published theoretical and experimental studies have focused on the suppression of shot noise due to negative correlation between current pulses caused by single electrons traversing the device. Such correlation may be introduced by Pauli exclusion, which limits the density of electrons in phase space, and/or by Coulomb repulsion, depending on the details of the structure and on the dominant transport mechanism [6-8], and make the pulse distribution subpoissonian, leading to suppressed shot noise.In particular, for the case of resonant tunneling structures, several theoretical and experimental studies have appeared in the literature [2][3][4][5][6][7][8][9][10][11], assessing that the power spectral density of the noise current S in such devices may be suppressed down to half the "full" shot noise value S full 2qI, i.e., that associated with a purely poissonian process.In this Letter, we propose a theoretical model and show experimental evidence of the opposite behavior, that is, of enhanced shot noise with respect to S full , which is to be expected in resonant tunneling structures biased in the negative differential resistance region of the I-V characteristic. An attempt to model such phenomenon has been presented in Ref. [13].We shall show that in such a condition Coulomb interaction and the shape of the density of states in the well introduce positive correlation between consecutive current pulses, leading to a superpoissonian pulse distribution, which implies a superpoissonian shot noise.First, we shall show an intuitive physical picture of the phenomenon, then we shall express it in terms of a model for transport and noise in generic resonant tunneling stru...

We propose a quantum mechanical approach to noise in resonant tunneling structures, that can be applied in the whole range of transport regimes, from completely coherent to completely incoherent. In both limiting cases, well known results which have appeared in the literature are recovered. Shot noise reduction due to both Pauli exclusion and Coulomb repulsion, and their combined effect, are studied as a function of the rate of incoherent processes in the well (which are taken into account by means of a phenomenological relaxation time), and of temperature. Our approach allows the study of noise in a variety of operating conditions (i.e., equilibrium, sub-peak voltages, second resonance voltages), and as a function of temperature, explaining experimental results and predicting interesting new results, such as the dependence of noise on filled emitter states and the prediction of both increasing and decreasing shot noise with increasing temperature, depending on the structure. It also allows the determination of the major contributions to shot noise suppression by performing noise measurements at the second resonance voltage.

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High-risk mHPV infection identified patients with persistent LSIL/CIN1 and may to help identify patients at higher risk of disease progression to HSIL+/CIN2+. Longer follow-up will clarify the role of mHPV testing in patient care. Cancer Cytopathol 2017;125:138-143. © 2016 American Cancer Society.