Gaussian generation-recombination is accepted to be a dominant mechanism of current
noise source in quantum well systems biased by electric field normal to the layers. Recent
experiments in n-type and p-type multiple quantum wells have revealed an additional
pronouncedly non-Gaussian excess current noise with a low cut-off frequency in the kHz
range. The non-Gaussian noise has been attributed to metastable spatial configurations of
electric field. The metastability is originating from negative differential conductance
caused by intervalley scattering in n-type wells and heavy and light holes tunneling in p-type
wells. At a constant bias the system randomly switches between high resistivity state
with low current flow and low resistive state with high current. The non-Gaussianity of
the noise is more pronounced in p-type wells where the time traces of current fluctuations
resemble closely two-level random telegraph signal. In n-type wells the telegraph-like
fluctuations have not been straightforwardly observed. The non-Gaussianity of the noise
in n-type systems has been revealed by nonzero skewness. The differences between noise
properties of between n- and p-type systems have been attributed to small capture
probability of electrons in n-type wells, as opposed to very high capture probability of
holes in p-type wells. As a consequence the noise of any p-type multi-well system is
dominated by the tunneling from the wells while in the n-type the noise appears as a
superposition of many fluctuators associated with individual wells.
Pronounced random telegraph signals have been observed in voltages measured across current-biased thin-film
YBa2Cu3O7-δ superconducting bridges containing laser-processed channels for easy vortex motion. The appearance of two-level and three-level telegraph noise in bridges with single and double laser-written channels, respectively, is interpreted as experimental evidence for intermittent channeled vortex flow in current induced dissipative state in
type-II superconductors.
The large increase in the flux-flow voltage noise, commonly observed in the vicinity of the peak-effect in superconductors, is ascribed to a novel noise mechanism. The mechanism consists of random injection of the strongly pinned metastable disordered vortex phase through the sample edges and its subsequent random annealing into the weakly pinned ordered phase in the bulk. This results in large critical current fluctuations causing strong vortex velocity fluctuations. The
excess noise due to this dynamic admixture of two vortex phases is found to display pronounced reentrant behavior. In the Corbino geometry the injection of the metastable phase is prevented and, accordingly, the excess noise disappears. The excess flux-flow noise in the peak-effect regime is dominated by vortex velocity fluctuations while the density fluctuations, frequently considered in the conventional flux-flow noise models, are negligibly weak. Strong nongaussian fluctuations are associated with S-shaped current-voltage characteristics. The spectral properties of the noise reflect the form of the frequency characteristics of the dynamically coexisting
vortex phases which is equivalent to the first order filter response. The cutoff frequency in the spectra corresponds to the time-of-flight of vortices through the disordered part of the sample.
We report on studies aimed at understanding and improving the intrinsic noise of high-performance sensors using a 2D electron gas channel confined by a quantum well in the pseudomorphic AlGaAs/InGaAs/GaAs heterostructure. MIS gated and ungated Hall sensors shaped as a Greek cross with dimensions ranging from 100 μm down to submicrometer range have been investigated. At room temperature the predominant low frequency Hall voltage noise originates from the ensemble of trapping/detrapping events occurring within the continuum of GaAs surface states. Its power spectral density can be deduced from independent measurements of the interface trap density-of-states by applying Shockley-Read-Hall dynamics and the Fluctuation-Dissipation Theorem. In fact, theoretical spectra calculated without any adjustable fitting parameter coincide closely with the experimentally measured ones. At cryogenic temperature this interface traps noise freezes out, thus revealing a much weaker intrinsic background noise with 1/f spectrum. For small sensors the intrinsic 1/f noise converts into one or a few lorentzians due to the action of individual random telegraph signals (RTS). For Hall crosses with an intersection of 4x4μm2, we find statistically less than 1 fluctuator per each decade of time constant at 77 K. Due to the random distribution of the elementary fluctuators, some of these small Hall crosses may show less low-frequency noise than much larger 60x60μm2 sensors.
Conference Committee Involvement (2)
Noise and Information in Nanoelectronics, Sensors, and Standards III
24 May 2005 | Austin, Texas, United States
Noise and Information in Nanoelectronics, Sensors, and Standards II
26 May 2004 | Maspalomas, Gran Canaria Island, Spain
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