Hot Electron Noise Research Articles

Transverse tunnelling time constant estimated from hot-electron noise in GaAs-based heterostructure

Electric noise characteristics of a triple-heterojunction AlGaAs/GaAs/AlAs/GaAs structure are measured at 10 GHz frequency for the electric field (≤ 1.3 kV/cm) applied in the interface plane. The maximum in the dependence of the longitudinal diffusion coefficient (deduced from the spectral density of current fluctuations) is observed at 1 kV/cm and interpreted as being brought about by back-and-forth transverse tunnelling of hot electrons between the quantum wells separated by a thin AlAs barrier, the wells being characterized by different electron mobility. The tunnelling time constant is found from the height of the maximum and, independently, from the quenching of the maximum in short samples.

Gamma -X intervalley-scattering time constant for GaAs estimated from hot-electron noise spectroscopy data.

The technique to investigate hot-electron noise in doped semiconductors at electric fields over 25 kV/cm is developed. The intervalley noise temperature at room temperature is found to saturate in GaAs at 15 000 K at fields over 100 kV/cm. From electric-field dependence of noise temperature, the intervalley scattering time of high-energy electrons from the \ensuremath{\Gamma} valley into the X valleys is estimated to be 30 fs ${\mathrm{\ensuremath{\tau}}}_{\mathrm{\ensuremath{\Gamma}}\mathit{X}}$60 fs. \textcopyright{} 1996 The American Physical Society.

The effect of strain on hot-electron and hole longitudinal diffusion and noise in Si and Si0.9Ge0.1

Monte Carlo methods are used to model the electron and hole high-field transport in both unstrained and compressively strained silicon and silicon-germanium alloy. The data are analyzed to determine in what way the thermal noise properties of the carriers are affected by compressive, in-plane strain. Results include the longitudinal diffusion coefficient, the longitudinal noise temperature, and the longitudinal noise spectral density, for electric fields in the range of 0–20 kV/cm. The results are qualitatively similar for silicon with 1% compressive biaxial strain and for Si0.9Ge0.1/Si(001). The effects of strain are found to be more pronounced for electrons than for holes and are primarily related to changes in the conductivity effective mass.

Detection and evaluation of self-heating effects in n+nn+ AlxGa1-xAs devices by noise temperature measurements

We have investigated self-heating effects in AlGaAs devices influencing hot electron noise temperature measurements. A technique for estimating the temperature change of the structure under test submitted to a high pulsed electric field has been developed. Simulation (electrical and thermal) results are satisfactorily compared with experimental data.

High frequency noise and diffusion coefficient of hot electrons in bulk Al 0.25 Ga 0.75 As

We present experimental results of hot electron noise in Si doped Al 0.25 Ga 0.75 As test structures using pulsed high-frequency noise measurements. Noise temperature and longitudinal diffusion coefficient as functions of field strength are compared with those of Si doped GaAs. We find significant changes at high fields. Results are discussed in regard of electron scattering mechanisms.

Hot-electron noise and diffusion in AlGaAs/GaAs

The electric field dependence of the microwave noise temperature and the diffusion coefficient are found to be significantly different for two sets of AlGaAs/GaAs structures with different spacer thickness and aluminium mole fraction. In the samples with a 'wide' quantum well (QW), one maximum of the diffusion coefficient is observed at fields below the threshold for the intervalley diffusion, but two maxima are characteristic of a 'narrow' QW with an intersubband gap wider than the KBTO. A microscopic explanation of the observed noise spectra of AlGaAs/GaAs is given and used to determine kinetic parameters of the heterostructures.

Suppression of hot-electron fluctuations in submicrometre semiconductor layers

A physical model is proposed for limitation and suppression of spectral intensity of hot-electron fluctuations in submicrometre semiconductor layers, where the thickness 2d of the sample is comparable to the electron energy relaxation length Lepsilon . We suppose two identical layer surfaces, no space charge and surface charges at zero bias, the electron temperature approach, and the surface velocity approximation. Electric field E and dimension 2d dependences of spectral densities of fluctuations, small-signal conductivities and noise temperatures are investigated. A decrease of the spectral intensity of hot-electron fluctuations and noise temperature takes place when 2d<Lepsilon in the range of fluctuation frequencies omega tau epsilon <<1, where tau epsilon is the electron energy relaxation time.

Experiments on hot electron noise in semiconductor materials for high-speed devices

Experimental results on noise temperature and spectral density of current fluctuations (electron diffusion) at high electric fields in silicon, gallium arsenide, and indium phosphide are presented. The dominant noise sources are discussed in their relation to electron scattering mechanisms. Physical backgrounds of high speed-low noise performance (noise-speed tradeoff) are considered. Suppression in short samples of the fluctuations having long correlation time constant and (or) high threshold energy is discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Influence of Al content x on hot electron noise in Al/sub x/Ga/sub 1-x/As n/sup +/nn/sup +/ devices: comparison with GaAs

Hot electron noise measurements are performed in Si doped Al/sub x/Ga/sub 1-x/As n/sup +/nn/sup +/ devices, for three different Al concentrations: x=0.15, 0.2, 0.25. Noise temperatures are obtained using a pulsed measurement technique as functions of electric field and frequency. Longitudinal diffusion coefficients D(E) are deduced at 4 GHz. Results are analyzed through the scattering mechanisms which greatly affect the electron velocity properties of Al/sub x/Ga/sub 1-x/As materials. Comparisons with n/sup +/nn/sup +/ GaAs devices are made.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Effect of hydrogen on hot electron noise in short samples of GaAs

We present experimental results on hot electron noise in untreated and hydrogenated samples of silicon-doped GaAs. Short n+-n-n+ structures are used to resolve noise sources arising from different mechanisms which dominate electron scattering. Passivation of centres of impurity scattering by hydrogen and the resultant effect on noise temperature and spectral density of current fluctuations are clearly observed at intermediate hydrogen doses (1017 cm-2): low-field mobility of electrons increases, electron heating by electric field is favoured, noise sources due to Gamma -L and Gamma -X intervalley transfer and resonant scattering of hot electrons are better resolved, especially at low temperatures. The effects at a hydrogen dose of 1018 cm-2 suggest that the impurity passivation is accompanied by formation of new scattering centres.

Comparative analysis of microwave noise in GaAs and AlGaAs/GaAs channels

Hot electron noise at 10 GHz microwave frequency is investigated in an AlGaAs/GaAs heterostructure channel with two-dimensional electron gas (2DEG), and the results are compared to those for 3DEG channels of GaAs. An experimental evidence of noise due to 2DEG⇆3DEG transfer at 80 K is presented. The related longitudinal diffusion of hot electrons in long 2DEG channels is found to dominate at the intermediate fields which are well below the threshold field for intervalley diffusion in GaAs. A tendency to suppress the intervalley noise and diffusionby the 2DEG⇆DEG transfer is observed at the high fields. Possible suppression of the dominant sources of microwave noise in modulation-doped field-effect transistor channels is discussed.

Hot electron noise in III-V heterojunction field effect transistors

The knowledge of hot electron noise properties in FETs and the dependence on biasing conditions and frequency is essential in device optimization. The recent development of submicron gate MODFETs with epitaxial III-V semiconductor heterolayers has considerably complicated the problem of producing accurate device models able to predict at the same time the static and microwave characteristics and the noise results as well. Low cost and fast simulators that can be implemented on small computers are in high demand in the device industry. In this paper the authors try to describe the present state of this problem.

The Mott diode as a heterodyne receiver element

This paper considers a novel doping profile for Schottky barrier mixer diodes called the Mott barrier. The structure consists of a metal-semiconductor junction in which the semiconductor's epitaxial layer is very lightly doped and thin enough so that it remains depleted even under substantial forward bias. It has been proposed that Mott barrier diodes will generate less noise and have lower series resistance-junction capacitance products than standard Schottky diodes, thus increasing the sensitivity and cut-off frequency of heterodyne receivers. In this paper, the band structure and electron transport properties of the Mott diode are evaluated. This analysis shows that the Mott diode actually will have a large series resistance-junction capacitance product and excessive hot electron noise, making it a poor candidate for high-frequency applications. Experimental results are presented which substantiate these conclusions.

Length dependent hot electron noise in doped GaAs

Hot electron microwave noise is studied in 0.2 … 7.5 micron-long samples of GaAs at strong electric fields at 80 K and 293 K ambient temperatures. A new noise source is observed in doped (3·10 17 cm −3 samples. This source is related to the impurity levels lying 0.2 eV above the principle edge of the conduction band. At a given electric field the doped short samples show a higher noise temperature as compared to pure samples of the same length. Onset of the resonance impurity scattering gives rise to efficient transformation of the drift energy into the chaotic one and stimulates the intervalley noise sources. The threshold voltages of these sources are determined. The enhanced hot electron diffusion is observed in the vicinity of the threshold voltages. The critical length is less than one micron in doped GaAs.

Hot-electron noise in two-valley semiconductors: An analytic model.

We present results for the hot-electron noise in two-valley semiconductors, such as GaAs, where intervalley transfer plays an important role. The noise is calculated by a Boltzmann--Green-function method. We obtain an analytic solution for a model with two valleys and three relaxation times. Using the measured low-field mobility, lower-valley mass, and valley separation energy \ensuremath{\Delta}, while adjusting three upper-valley parameters, we obtain good agreement with both experimental time-of-flight measurements and microwave noise measurements. We find that the hot-electron noise is very sensitive to the transport parameters, much more so than the velocity-field curve. In particular, the noise is very sensitive to the \ensuremath{\Gamma}-to-L scattering rate and our results indicate that experimental noise measurements might be used for determining this parameter.

Nonequilibrium current fluctuations in semiconductors: A Boltzmann-equation-Green-function approach.

We present a method for calculating nonequilibrium current fluctuations (i.e., hot-electron noise) in semiconductors based on the Green function to the time-dependent Boltzmann equation. The method is valid for nondegenerate semiconductors for which the Boltzmann equation describes the normal (i.e., time-independent) transport properties. We illustrate the method in uniform systems within the relaxation-time approximation. We find that the noise can either increase or decrease from its equilibrium value, depending on the band structure and the energy dependence of the relaxation time.

Comments on van der Ziel's “a generalized expression for diffusion noise and hot-electron noise at arbitrary drift velocities”

Comments on van der Ziel's “a generalized expression for diffusion noise and hot-electron noise at arbitrary drift velocities”

Supplementary remarks on “a generalized expression for diffusion noise and hot-electron noise at arbitrary drift velocities”

Supplementary remarks on “a generalized expression for diffusion noise and hot-electron noise at arbitrary drift velocities”

Analysis and Optimization of Millimeter-And Submillimeter-Wavelength Mixer Diodes

An analysis of the noise of millimeter- and submillimeter-wavelength mixers with GaAs Schottky diodes is presented. This analysis accounts for the correlation of the downconverted components of the time-varying hot-electron noise in the series resistance, and is thus accurate even for cryogenically cooled mixers operated at submillimeter wavelengths. This paper shows that the terms of the series-resistance noise correlation matrix are functions of the Fourier coefficients of the squared diode current F(I/sup 2/) rather than the square of the Fourier coefficients of the diode current [F(I)]/sup 2/, as has been previously presented in the literature. The analysis is used to evaluate the optimization of cryogenic mixer diodes. It is shown that minimization of the diode's I-V slope parameter V/sub 0/ is more critical than reduction of the parasitic elements for millimeter-wavelength operation, while at frequencies above 600 GHz (Lambda<0.5 mm), the junction capacitance is the most crucial parameter. Experimental results from several research groups working with a variety of mixers are presented to substantiate these results.

High-frequency noise and current-voltage characteristics of mm-wave platinum n–n+–GaAs Schottky barrier diodes

The noise power spectral density from 100 MHz to 88 GHz has been measured for forward-biased platinum n–n+–GaAs Schottky barrier diodes at room temperature. There appear to be five sources of noise: shot noise, Johnson noise, hot-electron noise, intervalley scattering noise, and trap noise. The magnitudes of these sources are dependent on the bias condition, frequency, and structural parameters as well as the quality of the material. A trap mechanism that may explain the frequency-dependent noise is suggested. The relative importance of each source is investigated for different diodes versus forward bias and frequency. The current-voltage characteristics were also investigated, and show features at high forward bias which are not predicted from simple theories.