Fluctuation and Noise Letters

Microscopic current fluctuations and conductance are inseparable. We present a unified kinetic theory of both quantized conductance and nonequilibrium noise in one-dimensional ballistic wires. We show that high-current ballistic fluctuations depend, directly and robustly, on carrier statistics. This is dramatically evident in the large noise peaks predicted to coincide with the quantized steps in the two-probe conductance. The outstanding features of nonlinear ballistic fluctuations are: (i) their observability by standard experimental techniques; (ii) their strong suppression by electron degenercy; (iii) their divergence in any model that ignores the explicit dynamics of dissipative scattering in the macroscopic leads; (iv) their numerical dominance over the noise predictions of the Landauer-Büttiker model. The nonequilibrium noise of hot ballistic carriers is strikingly sensitive to their inelastic energy loss on entering the leads. Uniquely and quantitatively, it characterizes the observed nonideality of quantized conductance.

Atomic diffusion of impurity centers is investigated as a possible origin of 1/f noise in semiconductors. Following the trace of an individual impurity center, the noise produced at a certain site is calculated; due to diffusion of centers this is an intermittent process. Besides generation-recombination (= g-r) noise, an excess noise is obtained which is attributed to diffusion of impurity centers. This excess noise exhibits 1/f noise and g-r burst noise. 1/f noise is attributed to the return time of a center to the origin; g-r burst noise is the noise produced by centers residing at a certain site. For a n-type strongly extrinsic semiconductor, the Hooge coefficient α of the present model is derived and impact of compensating acceptors or additional doping by shallow centers is investigated. Increasing the concentration of additional shallow centers α is decreased; an increase of concentration of compensating acceptors results in an increase of α. The temperature dependence of the Hooge coefficient α(T) is calculated and is compared with empirical findings.

The dependence of the 1/f noise on 2D electron concentration in the channel n_Ch of AlGaN/GaN Heterostructure Field Effect Transistors and Metal Oxide Semiconductor Heterostructure Field Effect Transistors has been studied and compared. The dependencies of Hooge parameter α_Ch for the noise sources located in the channel of the transistors on sheet electron concentration are found identical for both types of devices. The increase of the Hooge parameter α_Ch with the decrease of the channel concentration observed in both types of devices confirms that the noise sources are located in the region under the gate in the AlGaN/GaN heterostructure and that electron tunneling from the 2D electron gas into the traps in GaN or AlGaN layers is a probable noise mechanism.

We apply the quantum trajectory method to current noise in resonant tunneling devices. The results from dynamical simulation are compared with those from unconditional master equation approach. We show that the stochastic Schrödinger equation approach is useful in modeling the dynamical processes in mesoscopic electronic systems.

In this work, we experimentally investigate fundamental aspects of 1/f noise in silicon CMOS transistors, considering a broad group of technological families. We bring out some device down-scaling issues. A direct comparison between our experimental data and the noise dominant theories in MOS-FETs is dealt with.

We present evidence to support the idea that Stochastic Resonance (SR) and Brownian Ratchets (BR) share underlying physical principles. We examine the special case of a discrete-time ratchet, called Parrondo's games, and show that the addition of noise increases the rate of flow in the ratchet up to a certain point, after which the addition of further noise causes the rate of flow of decrease. We argue that the rate of flow of particles in a BR is analogous to the rate of flow of information in the case of SR.

We report detailed investigations of low-frequency excess noise in Ga-polarity GaN thin films deposited by RF-plasma assisted molecular beam epitaxy. The noise properties of the GaN thin films deposited with and without the intermediate-temperature buffer layers (ITBL) are studied in detailed to examine the effects of the ITBL on the noise. Substantial reduction in the flicker noise levels are observed for samples grown on ITBLs with a Hooge parameter of 3×10^-4, which is believed to be the lowest, to date, reported for GaN material. At low-temperatures, Lorentzian bumps originating from the generation-recombination processes are observed. Detailed studies of the temperature dependencies of the voltage noise power spectra have led to the formulation of a model for the observed low-frequency fluctuations. The model stipulates that the phenomenon arises from the thermally activated trapping and detrapping of carriers. The process results in the correlated fluctuations in the carrier number and the Coulombic scattering rate. Quantitative computation shows that number fluctuation dominates in our samples. Numerical evaluation of the deep-levels indicates substantial reduction in the trap density for the Ga-polarity GaN films.

Experimental studies on low frequency noise in bipolar junction transistors (BJT) including polysilicon emitter, hetero-junction bipolar transistors (HBTs) and silicon-germanium hetero-junction transistors (SiGe HBTs) are reviewed. The 1/f noise is treated in terms of mobility fluctuations. The validity of a new empirical relation between the 1/f noise corner frequency f_c (the frequency where the 1/f noise and shot noise are equal) and the peak cutoff frequency fr_peak is investigated. The experimental procedure to investigate the most dominant low-frequency noise source in the equivalent circuit is described. At medium frequencies, the white noise becomes dominant and the noise figure is calculated taking into account the emitter and base series resistance.