Search

We analyzed structural and electrical properties of axial Si-Ge nanowire heterojunctions produced by the vapor-liquid-solid growth method using Au nanoclusters as catalysts. The observed nonlinear current-voltage characteristics, strong flicker noise, and damped current oscillations with frequencies of 20–30 MHz are explained using a proposed Si-Ge nanowire heterojunction energy band diagram that includes energy states associated with structural imperfections, as revealed by transmission electron microscopy.We analyzed structural and electrical properties of axial Si-Ge nanowire heterojunctions produced by the vapor-liquid-solid growth method using Au nanoclusters as catalysts. The observed nonlinear current-voltage characteristics, strong flicker noise, and damped current oscillations with frequencies of 20–30 MHz are explained using a proposed Si-Ge nanowire heterojunction energy band diagram that includes energy states associated with structural imperfections, as revealed by transmission electron microscopy.

We propose a unified DC and flicker noise model for bottom-gate amorphous InGaZO (a-IGZO) thin film transistors (TFTs) with an etch stop layer (ESL) valid for subthreshold, linear, and saturation regimes. A recent study carried out by our group about the origin of 1/f noise in four ESL a-IGZO TFTs with gate lengths 15, 20, 30, and 50 μ m and a width of 100 μ m revealed that carrier number fluctuation is the dominant mechanism of flicker noise in these specific devices and the contact resistances do not significantly contribute to the overall noise level. In this paper, we extended the work to develop a physics based 1/f noise model for ESL a-IGZo TFTs. The unified model and parameter extraction method, a technique developed for accurate parameter extraction and modeling of TFT device characteristics, is adapted to develop the I-V model. The noise model is subsequently derived taking into account the observed correlated mobility fluctuation based on the unified 1/f noise modeling idea. Results showed an excellent agreement between the experimental and modeled data for both the DC and flicker noise behavior of sample ESL a-IGZO TFTs over a broad range of bias conditions, at 298, 315, and 333 K operating temperatures.

The low-frequency noise in AlGaN/GaN transmission line model structures has been investigated for a wide range of ambient temperatures and dissipated powers. A deviation of low-frequency noise from a 1/f dependence has been observed upon increasing the applied voltage. The effect correlates with the nonlinearity of current-voltage characteristics (CVC). The concept of nonequilibrium 1/f noise has been introduced to explain 1/f noise enhancement. A qualitative model connecting non-equilibrium noise with nonlinearity of the CVC via a common origin-nonuniform overheating of the structures-has been suggested. Furthermore, deviations of equilibrium noise from the 1/f law at low temperatures have been observed and studied. (C) 2004 American Institute of Physics.

A general circuit model is derived for the electrical noise of electrode–electrolyte systems, with emphasis on its implications for electrochemical sensors. The noise power spectral densities associated with all noise sources introduced in the model are also analytically calculated. Current and voltage fluctuations in typical electrode–electrolyte systems are demonstrated to originate from either thermal equilibrium noise created by conductors, or nonequilibrium excess noise caused by charge transfer processes produced by electrochemical interactions. The power spectral density of the thermal equilibrium noise is predicted using the fluctuation-dissipation theorem of thermodynamics, while the excess noise is assessed in view of charge transfer kinetics, along with mass transfer processes in the electrode proximity. The presented noise model not only explains previously reported noise spectral densities such as thermal noise in sensing electrodes, shot noise in electrochemical batteries, and 1/f noise in corrosive interfaces, it also provides design-oriented insight into the fabrication of low-noise micro- and nanoelectrochemical sensors.

Low frequency fluctuations in light intensity were measured from five different types of commercially available light emitting diodes with wavelengths from 375 nm to 740 nm and from two different halogen lamps. At low frequencies below 10–100 Hz some light emitting diodes (LEDs) can provide lower levels of noise than halogen lamps. A noise quality factor β is proposed in order to characterize noise behavior of LEDs.

This article describes the impact of a high-energy proton irradiation on the parameters of the Lorentzian noise overshoot, occurring in ultrathin gate oxide 0.10 μm partially depleted (PD) silicon-on-insulator metal-oxide-semiconductor field-effect transistors (MOSFETs), operated in the linear regime. It is shown that the drain current noise spectral density SI exhibits an increase after irradiation, while the Lorentzian time constant τ shows a different response to the 60/65 MeV protons in n- or p-channel transistors. In addition, the excess noise peak develops a pronounced radiation-induced dependence on the back-gate bias VBG, which is different for both device types: a strong increase of SI is found for the PD SOI p-MOSFETs, upon changing VBG into the accumulation regime, while in the first instance, the opposite is found for the n-MOSFETs. These observations are discussed in terms of a RC-filtered shot noise model and of the ionization induced positive charge trapping in the buried and isolation oxid...

Experimental data on the low-frequency noise in GaN/AlGaN heterostructure field effect transistors show that the spectral noise density of the drain current fluctuations, SI, close to the saturation voltage increases faster than the square of the drain voltage Vd. At drain voltages higher than the saturation voltage, SI decreases with a further increase in drain voltage. A model of noise behavior below saturation based on the tunneling mechanism of noise is in a good agreement with the data measured.

An advanced theoretical approach to understanding the carrier-density fluctuation noise in n-channel metal-oxide-semiconductor field-effect transistors in the nonequilibrium steady state is introduced. Starting with the current continuity condition, a partial differential equation for carrier-density fluctuation is, on the basis of the drift-diffusion current model, derived from the charge conservation equation. The simulated noise spectral density characteristics determined for two different diffusion constant values are compared. It is demonstrated that the transport noise is suppressed compared to the case in which only the drift current component is considered when deriving a theoretical formulation of transport noise. The suppression of carrier-density fluctuation power can be explained by the interference of the forward and backward propagating carrier-density fluctuation power, which is reasonable on the basis of quantum mechanical and statistical physics. Drain current noise power increases with d...

The physics of noise is a complex subject. It is often difficult to clearly identify the physical origin of the observed noise. Electronic noise at microwave frequencies is technologically very important and has been extensively studied. While it is well known that many physical phenomena give rise to output current fluctuations (i.e., noise) in a metal–oxide–semiconductor field effect transistor (MOSFET), few physical phenomena have a time constant that can contribute in the microwave range. Current physical models of MOSFET microwave noise are all based on thermal agitation of electrons (thermal noise). However, what is the correct temperature (lattice or electron) to use in the noise calculation is an ongoing debate in the literature. All the modeling efforts have been using noise measured from pristine devices as a test for validity. In this work, we studied the n-MOSFET microwave noise as a function of electrical stress induced degradation. Our experiments thus introduced a new dimension in the noise...

The low-frequency noise in GaN/AlGaN heterostructure field-effect transistors (HFETs) was studied in the temperature range from 8 to 300 K. A contribution of generation-recombination noise with extremely small activation energy Ea=(1−3) meV was observed at T

Nanomechanical resonators can be fabricated to achieve high natural resonance frequencies, approaching 1 GHz, with quality factors in excess of 10^(4). These resonators are candidates for use as highly selective rf filters and as precision on-chip clocks. Some fundamental and some nonfundamental noise processes will present limits to the performance of such resonators. These include thermomechanical noise, Nyquist-Johnson noise, and adsorption-desorption noise; other important noise sources include those due to thermal fluctuations and defect motion-induced noise. In this article, we develop a self-contained formalism for treating these noise sources, and use it to estimate the impact that these noise processes will have on the noise of a model nanoscale resonator, consisting of a doubly clamped beam of single-crystal Si with a natural resonance frequency of 1 GHz.

Conduction and low frequency channel noise of gallium–arsenide (GaAs) based pseudomorphic high electron mobility transistors are investigated. The following analysis takes into account both the noise source associated with the intrinsic part of the device and the sources located within the access path. In order to discriminate between these two noise origins, a model of the transistor conduction is proposed using only a few parameters which are easily extracted. It is shown that the intrinsic channel noise agrees with Hooge’s model with αH parameter about 3×10−4 for the studied technology. Moreover, the values of the access resistances are an important parameter to describe correctly the conduction and the noise behaviors.

This article describes the noise characteristics of various silicon-on-insulator insulated-gate pn-junction devices with anode-offset regions. The static characteristics of these devices are modeled for the noise analysis; the model is composed of a series of a metal-oxide-semiconductor field-effect transistors and the pn junction. It is shown experimentally that the noise power of the devices is proportional to In (n>0), where I is the anode current. Since the noise characteristics are not explained by the conventional theory, a phenomenological model is proposed. It is shown that the proposed basic model, which is compatible with the conventional Hooge model, can explain the experimental results. The influence of anode-offset length is also discussed and modeled.

We investigate low frequency conductivity noise in the drain-source channel of organic material field-effect transistors by measuring the spectra of current fluctuations for several values of the gate voltage Vgs and drain voltage Vds and find that it is 1/f. The samples are biased in the ohmic range of the applied Vds. The relative current 1/f noise is inversely proportional to the charge carrier numbers N generated by illumination or by varying the gate-source voltage. Hooge's empirical relation for the 1/f noise is validated for these organic semiconductors with an a¿0.01 for poly-thienylene vinylene and about 100 for pentacene thin film transistors. From geometry dependence of the noise we conclude that series resistance can be ignored for poly-thienylene vinylene field-effect transistors. However, some pentacene samples suffer from a noisy series resistance to the channel resistance. From the 1/f noise dependence on geometry and gate voltage bias we conclude that it can be used as a diagnostic tool for device quality assessment. ©2002 American Institute of Physics.

We report experimental results showing how the noise in a Quantum-Dot Infrared photodetector (QDIP) and Quantum Dot-in-a-well (DWELL) varies with the electric field and temperature. At lower temperatures (below ∼100 K), the noise current of both types of detectors is dominated by generation-recombination (G-R) noise which is consistent with a mechanism of fluctuations driven by the electric field and thermal noise. The noise gain, capture probability, and carrier life time for bound-to-continuum or quasi-bound transitions in DWELL and QDIP structures are discussed. The capture probability of DWELL is found to be more than two times higher than the corresponding QDIP. Based on the analysis, structural parameters such as the numbers of active layers, the surface density of QDs, and the carrier capture or relaxation rate, type of material, and electric field are some of the optimization parameters identified to improve the gain of devices.

We have measured the low-frequency voltage noise properties across mesa stacks of intrinsic Josephson junctions in Bi2Sr2CaCu2Oy (BSCCO) single crystals as a function of bias voltage. The BSCCO mesas with area of 160×40 μm2 were fabricated on the surface of cleaved BSCCO single crystals using standard photolithography and Ar ion-milling techniques. The measured noise voltage spectrum density SV(f ) had a 1/f dependence on frequency. The magnitude of the 1/f noise spectra was found to increase monotonically with the branch number in the I–V characteristic at fixed bias current, and no anomalously enhanced 1/f noise was observed.

We present a comparative analysis of the current spectral densities in a Si bipolar junction transistor (BJT) and a SiGe heterojunction bipolar transistor (HBT) of identical geometry performed by means of an ensemble Monte Carlo simulator self consistently coupled with a two-dimensional Poisson solver. We focus on the physical origin of the different noise sources in the transistors at rf when varying the injection level conditions. At low injection the spectral density of base current fluctuations, SJB(0), is governed by thermal noise related to the base resistance, while the collector spectral density, SJC(0), reaches a typical shot noise response. At high current density the onset of high injection in the base and the base push-out play an important role in the noise behavior of both transistors. Thus, SJC(0) deviates from the typical shot noise response. Hot carrier effects are also present. In the HBT, these effects are less important than in the BJT due to the SiGe/Si heterointerface, and SJB(0) can...

The low frequency noise in GaN field effect transistors has been studied as function of drain and gate biases. The noise dependence on the gate bias points out to the bulk origin of the low frequency noise. The Hooge parameter is found to be around 2×10−3 to 3×10−3. Temperature dependence of the noise reveals a weak contribution of generation–recombination noise at elevated temperatures.

Here we investigate dc characteristics, impedance versus frequency, and low frequency noise. The effect of current distribution on 1/f noise in polycrystalline silicon thin film transistors (TFTs) is discussed. We show that the channel impedance versus frequency roll induces spectra that could be misinterpreted above a corner frequency in terms of a frequency index ¿ in 1/f ^¿ with ¿ higher than 2. Moreover, ignoring the inhomogeneous current distribution leads to overestimation of the noise parameter. Whereas it seemed evident that the noise in TFTs can be interpreted in terms of carrier number fluctuation, the noise parameter variation versus the gate bias can be also understood in terms of mobility fluctuations by including the potential barrier evolution. ©2001 American Institute of Physics.

We have measured the temperature dependence of the charge noise power spectral density Sq in two-junction Al–Al2O3–Al single-electron transistors at temperatures from 85 mK to 4 K. Although individual Lorentzians are often visible, the noise spectra are dominated by excess low-frequency noise with a power-law dependence on frequency f where Sq∝1/fβ and β≃1. Below about 0.5 K, Sq is weakly dependent on the temperature T. Above 1 K, the charge noise Sq increases with T, and at 4 K Sq≈10−4 e2/Hz at 1 Hz, about a factor of 100 greater than at 85 mK.

Measurements of low-frequency electrical noise (LFN) in an in-phase gain-coupled distributed feedback lasers with etched quantum-well active-layers emitting at 1.3 μm wavelength have been conducted. In particular, the injected current dependence of LFN is investigated over a wide range of injection current (from 10−2 μA to 60 mA). Pure 1/f noise spectra were observed in all measurements. The current dependence of the 1/f noise strongly correlates to the I–V characteristics. We find that noise from different mechanisms dominates when the lasers operate in different ranges of injection currents.

We report on the flicker (1/f ) noise in pentacene organic thin film transistors (TFTs) of different designs. Our studies show that the TFT design affects the noise level and the noise dependence on the gate- and drain-source biases. The measured noise level was the lowest for the TFTs with a top source and drain contacts design. For these devices, the noise dependence at low drain current values resembled that for n-type crystalline Si metal–oxide–semiconductor field-effect transistors. The extracted Hooge parameter α, which allows comparing the noise level in different devices and materials, was 0.045 for the top-contact TFTs. This parameter value is several orders of magnitude lower than that for conducting polymers and only several times higher than that for hydrogenated amorphous Si (α-Si:H) TFTs. The bottom source and drain contacts TFTs had a much higher noise level with a noise dependence on the terminal voltages that differed from the noise voltage dependence for the top-contact TFTs. The Hooge parameter values were in the range of 5–20 for the bottom-contact TFTs. We estimated that the contact noise could be comparable to the channel noise for both top-contact and bottom-contact TFTs.

We investigate the noise properties of p-type Mg-doped GaN using low frequency noise spectroscopy. The epitaxial GaN:Mg films were grown on a sapphire substrate by metalorganic chemical vapor deposition in different laboratories. Generation–recombination (g–r) noise and one-over-f (1/f) noise are observed for temperatures above 250 K. The magnitude of the 1/f noise exceeds the g-r noise magnitude for frequencies less than 30 Hz, and the 1/f noise level is characterized by high values of the Hooge parameter, α≈1–150, indicating a high level of structural imperfection. In addition, the integrated noise power spectral density divided by the voltage squared in the frequency range of 1 to 30 Hz, correlates strongly with the structural imperfection of the sample as measured from the asymmetric rocking curve (ω scan) full width at half maximum. The generation-recombination noise is related to a high concentration trap level with an activation energy of 120±25 meV and a repulsive barrier that is possibly associat...

The mechanism of the formation of porous silicon (PS) is studied using flicker noise spectroscopy (FNS), a new phenomenological method that allows us to analyze the evolution of nonlinear dissipative systems in time, space and energy. FNS is based on the ideas of deterministic chaos in complex macro- and microsystems. It allows us to obtain a set of empiric parameters (“passport data”) which characterize the state of the system and change of its properties due to the evolution in time, energy, and space. The FNS method permits us to get new information about the kinetics of growth of PS and its properties. Thus, the PS formation mechanisms at n-Si and p-Si, as revealed using the FNS, seem to be essentially different. p-Si shows larger “memory” in the sequence of individual events involved in PS growth than n-Si (if anodized without light illumination). The influence of the anodization variables (such as current density, HF concentration, duration of the process, light illumination) onto the “passport data...

The low frequency noise properties of organic thin film transistors are studied here as a function of frequency and bias. Various n-channel and p-channel devices were evaluated and found to exhibit 1/f-type of noise in the 1 Hz–10 kHz range. The drain current noise is found to vary proportionally with drain current. The noise level is comparable to that found in Si metal–oxide–semiconductor field-effect transistors within the operation region of the devices, owing to the smaller drain currents in organic transistors, although the intrinsic noise is considerably higher in the organic transistors. The viability of using the organic materials in low noise circuits is demonstrated by a ring oscillator.

1/f noise investigations in thin film transistors with long channel and thin thickness of amorphous silicon film are presented. It is found that the noise behavior follows the mobility fluctuation model in ohmic and saturation regimes, whereas in the subthreshold conduction, a quadratic law versus the drain current is observed. The noise modeling is proposed taking into account the equations usually utilized for crystalline silicon metal–oxide–semiconductor field-effect transistors according to Hooge’s theory. Moreover, the Berkeley Short-Channel Insulated Gate Field-Effect Transistor Model is adapted to predict the noise levels. Two noise parameters have been extracted: The first is used in the subthreshold region, whereas we show that the second, directly related to Hooge’s parameter, is adequate to describe alone the noise in normal conduction up to the saturation.

Degradation mechanisms contributing to increased 1/f noise of n-channel metaloxide-semiconductor field-effect transistors (n-MOSFETs) after different hot-carrier stresses are investigated. It is demonstrated that for any hot-carrier stress, the stress-induced enhancement of 1/f noise is mainly attributed to increased carrier-number fluctuation arising from created oxide traps, while enhanced surface-mobility fluctuation associated with electron trapping at preexisting and generated fast interface states and near-interface oxide traps is also responsible under maximum substrate- and gate-current stresses. Besides thermal-oxide n-MOSFETs, nitrided-oxide devices are also used to further support the above analysis.

We investigated random telegraph signals and 1/f noise in a submicron metal–oxide–semiconductor field-effect transistor at low temperatures in the Coulomb-blockade regime. The rich noise characteristics were studied as a function of gate voltage, drain current, and temperature, both in and beyond the Ohmic regime. The results can be understood within a simple model assuming a uniform potential fluctuation of constant magnitude at the location of the dot. Clear signatures of electron heating are found from the noise at higher currents.

Low-frequency noise of hydrogenated-amorphous-silicon (α-Si:H) thin-film transistors (TFTs) with a thin active layer and an inverted staggered device structure operating in the conducting mode has been investigated. Pure 1/f-noise spectra were observed. The results show that the physical location of the noise in α-Si:H TFTs is different from that in crystalline metal–oxide–semiconductor field-effect transistors. The noise contributions from the channel and interface have been determined for the device operating in different modes. The 1/f noise of α-Si:H TFTs stems from the channel when the device is operated in the linear region at high gate voltages. However, the 1/f noise of α-Si:H TFTs generated at the interface becomes significant when the device is operated in the saturation region. The interface noise can be explained by the number fluctuation model (ΔN model). The channel noise can be explained by either the ΔN model or the mobility fluctuation model (Δμ model).

Low frequency noise in 6H-SiC ion implanted p–n diodes has been investigated. The noise measurements were performed under forward bias over a wide temperature range from 77 to 300 K and frequency range from 10 to 100 kHz. Three diodes with different areas A1, A2, and A3, (A1

Low frequency noise in polysilicon emitter bipolar transistors (BJT) with different emitter areas (AE) was studied. In BJTs with submicron emitter area, random telegraph signals of different amplitudes and frequencies were found. Averaging of noise spectra from different submicron BJTs gives 1/f noise of the same level (normalized to the emitter area) as 1/f noise found in transistors with large emitter areas. The sheet density of traps (NT) located within the polysilicon–crystalline silicon interfacial layer and responsible for 1/f noise was estimated to be ⩾3×108 cm−2.

Dark current fluctuations in three types of multiquantum well (MQW) GaAs/AlGaAs avalanche photodiodes have been investigated. This work investigated both forward and reverse biases and furthered the understanding of the physics of noise in MQW structures used in photodetection (avalanche photodiodes) and emitters (semiconductor lasers). Under reverse bias, the increase of dark current and flicker noise compared with a classical PIN junction or Schottky junction is caused by thermionic field effect (TFE) conduction at the MQWs barriers. A method is developed as a function of temperature to detect the TFE at each barrier of the MQW before the onset of multiplication. Decreasing temperature is known to produce an increased resistance limit across an MQW emitter photodiode. Under forward bias, white and flicker noises are governed by the increase of resistance limit.

We report measurements of voltage fluctuations in magnetic tunnel junctions which exhibit both high and low magnetoresistance (MR). The voltage noise power normalized to the square of the junction bias voltage was 10−14/Hz at a frequency of 1 Hz in a high MR junction. Low MR junctions had significantly higher noise power at 1 Hz and the origin of the noise was not magnetic. In these junctions, random telegraph noise was observed over a wide range of temperatures and junction biases. The results are consistent with a two-channel model of conduction, one of which is spin independent and gives rise to large noise. A noise measuring technique provides evidence for bias-dependent current-path rearrangements. The data support the existence of an inhomogeneous (filamentary-like) current-flow pattern across the tunnel junction associated with the spin-independent channel.

First order and low-frequency noise measurements are performed on GaInP/GaAs heterojunction bipolar transistors. The base current is decomposed into different components. Passivated transistors exhibit higher gain values, hence the passivation layer limits recombinations on the extrinsic device. Noise is measured in the 1 Hz–100 kHz frequency range on common-emitter-mounted transistors. The 1/f component is analyzed. The emitter series resistances are extracted. The proximity of the base contact on the smaller devices lead to a higher noise level due to enhanced recombinations. Extrinsic and intrinsic phenomena are put forward with the help of noise analysis versus base current and collector current density. An attempt is made to locate the 1/f noise sources. Unlike first order measurements, noise characterization shows that the passivation layer can be at the origin of recombination-type phenomena.

Conduction and low-frequency noise are analyzed in hydrogenated amorphous thin film transistors with small channel length. From current–voltage characteristics a set of conduction parameters is extracted pointing out parasitic resistances in series with the active channel. The low-frequency noise behavior is studied by means of the small equivalent circuit of the device. Intrinsic channel noise is separated from access resistance noise. Channel noise variations versus device biases agree with Hooge’s theory (carrier mobility fluctuations) but the noise levels are greater than in crystalline metal-oxide-semiconductor transistors. For high drain current 1/f noise in access series resistances prevails and becomes the main noise source. So, the results show the important part taken by these resistances in conduction and noise. Some comments for the design of thin film transistors are given.

We report on low-frequency noise characteristics of visible-blind GaN p-n junction photodetectors. Carrier hopping through defect states in the space charge region, believed to be associated with dislocations, is identified as the main mechanism responsible for the dark conductivity of the photodiodes. Under reverse bias, the dark current noise has the 1/f character and obeys the Hooge relation with α≈3. Under forward bias, we observe generation-recombination noise related to a trap level with the activation energy of 0.49 eV. Under illumination, detectivity is found to be shot noise limited. The noise equivalent power of a 200×200 μm2 photodetector is estimated at 6.6×10−15 W/Hz1/2 at a bias of −3 V.

The noise in current biased aluminium single electron tunneling (SET) transistors has been investigated in the frequency range of 5 mHz = 10 Hz, we find the same input charge noise, typically QN = 5 × 10–4 e/Hz1/2 at 10 Hz, with and without the HF shielding. At lower frequencies, the noise is due to charge trapping, and the voltage noise pattern superimposed on the V(Vg) curve (voltage across transistor versus gate voltage) strongly depends on the background charge configuration resulting from the cooling sequence and eventual radio frequency (rf) irradiation. The measured noise spectra which show both 1/f and 1/f1/2 dependencies and saturation for f

Microfabricated magnetoresistive elements based on either the anisotropic or the giant magnetoresistance effect were tested for their frequency dependent resistance noise behavior at room temperature in a dc magnetic field, using a dc sense current. Thermal resistance noise was the dominant noise source above about 10 kHz. At low frequencies the resistance noise was found to be dominated by a 1/f contribution that depends on the applied magnetic field. The 1/f noise is relatively low and field independent when the element is in a saturated state and contains a relatively large and field dependent excess contribution when the magnetic field is in the sensitive field range of the element. The 1/f noise level observed in saturation is comparable to the 1/f noise level found in nonmagnetic metals; the excess noise has a magnetic origin. The variation of the excess noise level with the applied dc magnetic field can be explained qualitatively using a simple model based on thermal excitations of the magnetization direction.

Experimental results on low frequency noise in quasiself-aligned bipolar n-p-n junction transistors, with widely varying emitter/base junction dimensions are presented and compared with former results obtained on devices of the same type. The power spectral density of base current fluctuations was found to depend linearly on the inverse of the area of the emitter/base interface junction, implying localization of the low frequency noise sources on the interface, rather than on the transistor perimeter. An application of current-to-voltage converters for studies of current fluctuations is also discussed and compared with a more conventional technique.

Local measurements of structural characteristics such as intrinsic microstrain along the c axis of the lattice e=δc/c and its mean square fluctuation 〈e〉, oxygen deficiency x, cation composition, etc. were performed on epitaxial YBa2Cu3O7 films grown on various substrates (MgO, BaSrTiO3/MgO, SrTiO3, LaAlO3, ZrO2/Si, Al2O3). A number of film microstrips were fabricated and the normalized flicker noise intensity (Hooge parameter α) and the resistivity ρ at 300 K were measured at each characterized point. A theoretical model was developed that explains the observed first growth of α with 〈e〉 and the well-known high level of the normal-phase flicker noise in various high temperature superconducting compounds. Comparison of the experimental and simulated dependence of α on 〈e〉, frequency, and temperature permits one to determine numerically the theoretical parameters of the double-well potential with minima located at the chain (O1) and empty (O5) oxygen lattice positions of the CuO plane.

The experimental requirements for low frequency electrical noise measurements of single electron tunneling (SET) semiconductor samples are discussed and a two-channel cross-correlation spectrum analysis method combined with ultralow noise detection is proposed which gives 10 mK noise temperature resolution. We emphasize the effect of the high frequency photon radiation originating from the external circuit which may strongly affect sub-kelvin low frequency noise measurements if not filtered. We quantitatively show that hot photons are important as a mechanism of activation of electron traps for semiconductor SET devices, increasing low frequency 1/f or telegraphic noise, and as a mechanism to increase the electronic temperature. We describe a new type of cryogenic coaxes whose attenuation drastically thermalizes the photons. As a check, we show for the first time resonant tunneling peak linewidths in the Coulomb blockade regime decreasing with temperature down to ≃60 mK.

Low-frequency noise measurements are performed on classical Si bipolar transistors and on AlGaAs/GaAs heterojunction bipolar transistors (HBTs) mounted in a common-emitter configuration. Expressions for the spectral densities are derived taking into account a correlation between base and collector noise sources ib and ic. Values of emitter series resistances and of the base ideality factor are determined from these noise measurements. Then the spectral densities related to ib and ic as well as the cross-spectrum are extracted. In the case of classical Si transistors, the excess noise is attributed to the current noise source ib. The effect of the base series resistance is shown on the white noise. For the HBTs, the white noise is not reached. The excess noise is attributed to the correlated current noise sources ib and ic. From the analysis of the current spectral densities with base current the increase of correlation with bias is revealed. The extracted current spectral densities provide the foundation ...

Low-frequency noise measurements were performed on heterojunction bipolar transistors (HBTs) and presented in part I of this article. These measurements revealed a partial correlation between base and collector noise current sources. With the help of the current spectral densities determined in part I, the coherence function is calculated and studied versus bias in this second part. Important values of the coherence function are obtained at the highest bias. Then the spectral densities Sc and Snc associated to the correlated and uncorrelated parts of the collector current noise source are extracted and analysed. All spectra exhibit excess noise. A difference in shape is clearly observed because of an important generation-recombination component occurring around 1 kHz on the correlated part only. To compare the behavior of different transistors a normalized coupling coefficient is introduced. The correlation is seen to increase with the scaling-down of devices. The investigation of the coupling coefficient...

The bulk low frequency noise has been investigated in the 4H silicon carbide polytype. In the temperature range of 300–550 K the noise spectral density S is proportional to f−1.5, where f is the measurement frequency. A very low noise level has been observed for the bulk noise. At 300 K, the Hooge constant α is as small as (2–4)×10−6 at f=20 Hz and α⩽5×10−7 at f=1300 Hz. At T⩾600 K, the generation-recombination noise of a local level makes the main contribution into the total low frequency noise. The electron capture cross section σ of this level depends very strongly on temperature. In the temperature range of 620–700 K, the temperature dependence of σ can be expressed as σ∼exp(−E1/kT), with an activation energy E1 as high as 2.7 eV.

According to a barrier photoconductance theory recently developed, two current noise sources can be envisaged, related respectively to the fluctuation of the barrier height (photoinduced noise component) and to the trapping–detrapping processes in shallow states within the photoconducting material (g–r and 1/f noise component). It is shown that the first noise component, which can be separated by the second one, gives information on the energy gap and on the photoionization cross section of the deep energy levels of the photoconducting material. In particular for thin films it will be shown that the photoionization cross section of the deep energy levels varies inversely to the total number of photons impinging on the photoconductor and proportionally to the noise power spectral density as the photon energy changes. Such relationship suggests that the wavelength dependence of the noise power spectrum provides the correction to be taken into account if the constant photocurrent method is used and the variations of the minority carrier lifetime with the photon energy cannot be disregarded. Results concerning the energy gap and its temperature dependence, in the interval ranging from the room temperature to 200 K, are reported and compared with the results found in the literature for CdS based samples. The photoionization cross section of the deep centers as a function of the photon energy, at room temperature, is reported for the same sample. Such quantities have been obtained by measuring the spectral density of the photoinduced noise vs wavelength at constant photoconductance value. As for the other kinds of noise spectroscopy, the main advantage of the present method is to work out in the operative condition of the semiconductor device.

A new model for the low frequency (LF) noise in the base current of polysilicon emitter bipolar junction transistors (BJTs) is proposed. This model is based on the carrier number fluctuation approach and satisfactorily accounts for the base current noise characteristics. The base current fluctuations are ascribed to surface and volume noise sources. The surface noise arises from the low frequency fluctuations of the surface generation–recombination base current component due to the dynamic trapping–detrapping of carriers into/from slow states located in the spacer oxide at the periphery of the emitter/base junction. The volume noise results from the intrinsic fluctuations of the diffusion base current due to the carrier number fluctuations in the emitter or at the emitter–base junction. This LF noise model has been applied to BJTs subjected to hot carrier stress after reverse biasing of the base–emitter junction. The evolution of the base current noise characteristics after stress clearly demonstrates tha...

The steady‐state Nyquist theorem for multi‐terminal semiconductor devices, which describes the short‐circuit thermal noise currents in arbitrarily shaped multi‐terminal semiconductor devices, is reinvestigated. The concept of the equipotential surfaces for small ac signals is found to be wrong, which forces us to introduce a new approach to find the equipotential surfaces for noise voltages. Using this new approach, we rederive the steady‐state Nyquist theorem with the same results as in the previous derivation, and extend it to the hot carrier regime. Using the extended theorem, we express the minimum noise figure for microwave field effect transistors as a function of the measurable device parameters with no fitting constant. The derived minimum noise figure is shown to reduce to a simple form, which can also be used as an empirical relation with one fitting constant. This simple form can explain the experimental results very well in wide frequency ranges, and gives through a clear mathematical relation...

Low-frequency noise measurements are performed on heavily doped p-type GaAs transmission line models. Excess noise exhibits 1/f noise and generation-recombination (GR) noise components. A study of the GR components vs device geometry shows the spectral densities due to contact resistances to be negligible. Thus the noise sources due to the volume resistances are predominant, and have to be located in the bulk layer or in the space-charge region of the devices. These two possibilities concerning the location of the GR noise sources are investigated. For both cases, expressions for the variance and the relaxation time associated to fluctuations in the charge carriers are given. The comparison between the experimental data with the theoretical results shows that the GR noise sources are located in all probability in the space-charge region.

This paper describes experimental results on low frequency noise in several types of polysilicon‐emitter NPN bipolar junction transistors. The experimental data were modelled using a combination of 1/f noise, generation‐recombination noise (g‐r), and shot noise, and good agreement between model calculations and experimental measurements were obtained. Observed differences in the experimental low frequency noise spectra of devices with similar geometry and under similar biasing conditions could be explained by the differences in the generation‐recombination (g‐r) noise contributions. Experiments were performed on devices with emitter areas varying from 1.6 to 144 μm2, and it was found that the magnitude of the flicker noise contribution KF varied inversely with emitter area AE or emitter perimeter PE. The fact that KF∼A−1E or KF∼P−1E is explained by the observation that AE∼PE within fabrication errors/tolerances. Using a set of 3.2 μm2 BJTs with pronounced g‐r noise, input current noise was measured at dif...

Effects of the gate dielectric nitridation on the flicker (1/f) noise characteristics of submicron metal oxide semiconductor field effect transistors (MOSFETs) are reported. Low‐frequency (1/f) noise measurements on nitrided and non‐nitrided gate oxide MOSFETs of the same geometry have been carried out, showing different noise behavior with respect to the flicker noise amplitude and bias dependence. It is found that gate oxide nitridation not only increases the flicker noise amplitude, but also enhances the correlated mobility noise mechanism. The two orders of magnitude higher noise measured in nitrided structures is consistent with the approximately two orders of magnitude increase of the nitrided gate conductance reported in the literature.