Characterization of individual electron traps in amorphous Si by telegraph noise spectroscopy

Rogers, Charles T.; Buhrman, R. A.; Kröger, H.; Smith, L. N.

doi:10.1063/1.97436

Cited by 41 publications

(9 citation statements)

References 14 publications

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“…In amorphous-silicon Schottky barriers, one invariably encounters random telegraph noise. [9][10][11][12][13] Switching amplitudes as high as 20% of the total resistance have been observed. The random telegraph noise seems to be well explained by a modulation of the conductance of a transport path through the tunnel barrier due to fluctuations of the barrier height induced by trapping and detrapping of charge carriers at nearby traps.…”

Section: Introductionmentioning

confidence: 90%

Resistance fluctuations in hydrogenated amorphous silicon: Thermal equilibrium

Verleg

Dijkhuis

1998

Phys. Rev. B

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Resistance noise measurements are presented of intrinsic hydrogenated amorphous silicon films as a function of voltage and temperature in the dark. The noise displays Gaussian statistics pointing to a large number of independent noise sources. It is demonstrated that the spectral dependence and temperature dependence are the result of a large number of independent thermally activated fluctuators. A distribution of activation energies for the characteristic rates is obtained from the measurements that peak at 0.85 eV with a full width at half maximum of ϳ0.2 eV. The attempt rate amounts to 7ϫ10 12 s Ϫ1 . We discuss general mechanisms for mobility fluctuations and number fluctuations due to generation and recombination of free carriers. A model for generation-recombination noise in a semiconductor with localized electronic states distributed throughout the mobility gap appears consistent with both the variance of the fluctuations and the temperature dependence of the rate constants. We identify the activation energy and attempt rate as the barrier limiting thermal emission of holes from defect states to the valence band. The width of the distribution of activation energies points to inhomogeneous broadening due to band bending. Light-induced metastable changes in the material are observed to affect the variance quite significantly. The present measurements and analysis of the noise under equilibrium conditions pave the way to successfully examine nonthermal equilibrium fluctuations in the photoconductivity and under injection conditions, which is the subject of the accompanying paper in this volume.

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Section: Introductionmentioning

confidence: 90%

Resistance fluctuations in hydrogenated amorphous silicon: Thermal equilibrium

Verleg

Dijkhuis

1998

Phys. Rev. B

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“…Although we have insufficient high-temperature data to determine accurately the quantities N u /N d and E u -E d , an extrapolation of our measurements to high temperature always gives N u /N d > 1; therefore, the traps spend more time in the up (charged) state than in the down (uncharged) state as the temperature increases This conflicts with our expectation that N u /N d -+ 1 as T-> oo (the large degeneracy of conduction electrons in the electrodes should dominate both states) and suggests that a more complex model of the trap system may be required. 6 ' 7 In particular, because of the large bias voltage, nonequilibrium effects will complicate interpretation of the temperature data. lifetimes for three different traps which display a wide range of behaviors.…”

Section: Should Then Vary As T -Exp(e a /Kt)mentioning

confidence: 99%

Direct lifetime measurements and interactions of charged defect states in submicron Josephson junctions

Wakai

Harlingen

1987

Phys. Rev. Lett.

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We have measured the emission and capture times of individual electron traps residing within the tunneling barrier of very small-area (<0.05 //m 2 ) Josephson junctions. The voltage-bias dependence of the times is consistent with a simple nonequilibrium model in which the bias enhances the rate for electrons to tunnel into the trap from one side of the barrier and exit out the other. Some junctions show clear evidence of interactions between traps, and for certain bias conditions the noise displays predominantly series kinetics.PACS numbers: 85.25.+k, 73.20.-r, 74.50.-fr Small-area tunnel junctions have recently been the focus of a number of low-frequency noise studies. 1 " 4 Unlike larger systems where the low-frequency noise exhibits a rather featureless \/f power spectrum, tunnel junctions can be made so small that the discrete nature of the underlying microscopic processes becomes apparent in the noise. This was first demonstrated by Rogers and Buhrman x who showed that the noise-power spectra of their junctions were dominated by a small number of Lorentzian features arising from the trapping and untrapping of single electrons into localized defect states within the tunneling barrier. The trapped electron alters the junction conductance by charging a small region about the trapping site, thereby blocking conduction through this channel. The voltage noise contributed by one such trap displays a series of discrete switching events, resembling a random telegraph signal, characterized by electron emission and capture times. Because the trapping couples to the junction voltage in such a simple, distinctive fashion, it is possible under certain favorable conditions to observe directly the switching behavior of one or several of these traps. In this Letter we report lifetime measurements of charged defect states in very small-area Josephson junctions under various temperature and voltage-bias conditions. The lifetimes show only a weak temperature dependence below 4 K, consistent with previous findings 2 ' 3 that the trapping process displays tunneling kinetics at low temperatures. In contrast, the emission and capture rates are both enhanced significantly by the application of a voltage bias, regardless of polarity. We propose a simple model to explain this behavior. In addition, the noise does not always exhibit a simple superposition of random telegraph switching when several traps are active at the same time; instead, interactions between the traps can produce a voltage noise that displays series kinetics. These observations show that the low-frequency noise of this system cannot always be described by a simple parallel-kinetics model composed of independent fluctuators.Using electron-beam lithography and a PblnAu-In2C>3-Pb edge-junction technology, we fabricate tunnel junctions with areas of <0.05 /im 2 having normal-state resistances on the order of 1 kn. When the junction is biased at voltages greater than 2A/e, charge trapping produces a voltage noise which scales with the normal resistance and the bias cu...

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“…There have been numerous studies of RTN and 1/f noise in semiconductors and in magnetic tunnel junctions [1,18,19], as well as observation of both 1/f and RTN in other systems [20], but an unambiguous quantification of the individual, discrete RTN signals leading to the 1/f noise spectrum has not yet been explicitly demonstrated.…”

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confidence: 99%