Shot-noise suppression in Schottky barrier diodes

Abstract

We give a theoretical interpretation of the noise properties of Schottky barrier diodes based on the role played by the long range Coulomb interaction. We show that at low bias Schottky diodes display shot noise because the presence of the depletion layer makes the effects of the Coulomb interaction negligible on the current fluctuations. When the device passes from barrier to flat band conditions, the Coulomb interaction becomes active, thus introducing correlation between different current fluctuations. Therefore, the crossover between shot and thermal noise represents the suppression due to long range Coulomb interaction of the otherwise full shot noise. Similar ideas can be used to interpret the noise properties of other semiconductor devices. © 2000 American Institute of Physics. ͓S0021-8979͑00͒03418-6͔It is well known that, in the absence of 1/f contributions, excess noise in Schottky barrier diodes ͑SBD͒ exhibits shot noise followed by thermal noise ͑neglecting hot-carrier effects͒.1,2 Shot noise is attributed to the presence of a barrier which controls the exponential increase of current with applied voltage. By contrast, the thermal behavior is attributed to the series resistance which controls the more or less linear increase of the current at the highest voltages. A phenomenological approach to describe the cross over from shot to thermal behaviors is to express the current spectral density, S I , as the partition between two noise generators as 1,2where Ī is the average electric current, q the electron charge, R j the junction resistance, R s the series resistance, k B Boltzmann's constants, and T the temperature. Microscopic approaches at hydrodynamic 3,4 and kinetic levels 5,6 confirm the above expression without resorting to two independent noise sources, but providing a selfconsistent solution of the dynamics together with the Poisson equation. However, a physical interpretation of the noise properties of SBD, and in particular of the crossover between shot and thermal noise, is still lacking in the current literature and constitutes an intriguing question.The aim of this article is to address this issue by showing that the crossover between shot and thermal noise behaviors represent the suppression due to long range Coulomb interaction of the otherwise full shot noise. This suppression occurs in SBD when the device passes from barrier to flatband conditions because of the following: By increasing the free carrier concentration the originally negligible screening effects due to the Coulomb interaction become relevant, thus acting as a shot noise suppressor. Accordingly, when controlled by screening effects carrier number fluctuations give a negligible contribution to the total noise power, which is now practically given by only the velocity fluctuations, thus providing thermal noise.The starting point of our approach is the nondegenerate fluctuating drift-diffusion equation which, for the case of one dimensional geometries and low frequencies, iswhere I is the instantaneous electric current, A th...

Shot Noise in Linear Macroscopic Resistors

“…According to the present view, the fact that shot noise is not observed in macroscopic resistors made of good conductors (e.g., metals) is due to the strong correlations induced by the long range Coulomb interaction in these samples that inhibits the pileup of charge carriers under realistic experimental conditions, rather than due to the presence of inelastic scattering processes, as sometimes claimed in the literature [5][6][7]. It is worth noting that the absence of long range Coulomb correlations is also at the basis of the presence of shot noise in vacuum tubes and ballistic diodes under saturation [17] and Schottky barrier diodes [18] or number fluctuations in nondegenerate Fermi gases [19]. The strong dependence on temperature of the resistivity of semi-insulating CdTe [12] allows us to perform experiments for different sample resistivities by simply varying the sample temperature.…”

Optimization of Passive Low Power Wireless Electromagnetic Energy Harvesters

“…The measured impedance of the HSMS-286C diodes at low frequencies (< 60 MHz) shows pronounced fluctuations. The low-frequency excess flicker noise and the shot noise observed in the HSMS-286C have been studied by several authors [31–33]. The pronounced presence of trap states in the depletion region of the semiconductor, mobility fluctuations in carriers, edge effects among other reasons is reported to cause deviations from the ideal Schottky diode behavior and hence generation-recombination noise for some diodes such as the HSMS-286C [34].…”

“…Therefore, the issue is not only how efficient a wireless EM harvester is in converting RF to DC power, but also what the output DC voltage and current of the EM harvester are at the RF input power level [38]. Equations (11,24) and (33) show that the maximum voltage sensitivity of a coupled resonator system or an RF to DC power converter is mostly related to the load and the source resistances at resonance. Therefore high voltage sensitive wireless EM harvester can be achieved with a diode voltage doubler with a very high input resistance relative to the antenna source without the need to cascade the diodes as in voltage multipliers.…”