Giant suppression of shot noise in double barrier resonant diode: a signature of coherent transport

Abstract

Shot noise suppression in double barrier resonant tunnelling diodes with a Fano factor well below the value of 0.5 is theoretically predicted. This giant suppression is found to be a signature of coherent transport regime and can occur at zero temperature as a consequence of the Pauli principle or at sufficiently high temperatures above 77 K as a consequence of a long-range Coulomb interaction. These predictions are in agreement with experimental data.Since its realization [1], the double barrier resonant diode (DBRD) proved to be an electron device of broad physical interest because of its peculiar non-Ohmic current voltage (I-V) characteristic. Indeed, after a strong superOhmic increase of current, it exhibits a negative differential conductance and eventually hysteresis effects [2]. Even the shot noise characteristics are of relevant interest, since suppressed as well as enhanced shot noise with respect to its full Poissonian value has been observed (see [3] for a review on the subject). These electrical and noise features are controlled by the mechanism of carrier tunnelling through the double potential barriers. The microscopic interpretation of these features is found to admit a coherent [4] or a sequential [5] tunnelling approach. The intriguing feature of these two approaches is that from the literature, it emerges that both of them explain the I-V experimental data as well as most of the shot noise characteristics. Therefore, to our knowledge, there is no way to distinguish between these two transport regimes and the natural question whether the tunnelling transport is coherent or sequential remains an unsolved one.The coherent approach to shot noise in DBRD has received wide attention since the first experimental evidence by Li et al [6] of shot noise suppression with a minimum value of the Fano factor γ = S I /(2qI ) = 0.5, where S I is the current spectral density and q the absolute value of the unit charge responsible of current. Remarkably, most of the coherent approaches developed so far predict a maximum suppression γ = 0.5 even if there is clear experimental evidence of suppression below this value (here referred as giant suppression) [7][8][9] down to values of γ = 0.25 [8,9]. To this purpose, some authors obtained theoretical values of the Fano factor just below the value of 0.5, 0.45 [10] and 0.38 [11], respectively. However, the physical interpretation of these results remains mostly qualitative and quoting [3] this direction of research looks promising but certainly requires more efforts.In this letter, we announce that a giant suppression of shot noise occurring before the peak value of the current is a signature of coherent transport in DBRDs. To this purpose, we present a theoretical model which predicts this phenomenon and is validated by experiments.The typical structure here investigated is the standard symmetric double well reported in figure 1. We denote by

Reply to Comment on Giant suppression of shot-noise in double barrier resonant diode: a signature of coherent transport

“…We also disagree that finding a Fano factor below 1/2 is strictly related to this approximation. As it is clear from figure 2 of our paper [1], there is wide region up to ξ = −10 for f = ∞ and f = 15 where Fano factor is below 1/2. In this region the resonant level is situated higher than the band edge of the emitter and the energy difference between them is greater than , thus the influence of the edge on L is neglibible in calculating the transparency.…”

A novel SWIR detector with an ultra-high internal gain and negligible excess noise

“…Interestingly, we have measured excess noise factors that are consistently below unity, indicating shot noise suppression in our devices. Such behavior might be resulted from the nano-injector, since shot noise suppression has been predicted theoretically 8 and measured experimentally 9,10 in similar structures.…”

Comment on Giant suppression of shot noise in double barrier resonant diode: a signature of coherent transport

“…An experimentally observed suppression of the Fano factor below 1/2 is argued to be a signature of coherent tunnelling. In this comment we do not address the experimental aspects but strongly contest the theoretical discussion of [1].…”

“…A recent letter [1] presents experimental data and a theoretical discussion of shot noise in a resonant double barrier [2]. An experimentally observed suppression of the Fano factor below 1/2 is argued to be a signature of coherent tunnelling.…”