Hot Electron Noise Research Articles

Experimental Investigation of Drain Noise in High Electron Mobility Transistors: Thermal and Hot Electron Noise

Experimental Investigation of Drain Noise in High Electron Mobility Transistors: Thermal and Hot Electron Noise

High-field transport and hot-electron noise in GaAs from first-principles calculations: Role of two-phonon scattering

The scattering of electrons by phonons in semiconductors has been assumed to be dominated by the lowest-order process involving a single phonon. Using a new numerical approach to incorporate the next-leading-order process involving two phonons into high-field transport calculations from first principles, the authors find here that the two-phonon process contributes nearly as much as the single-phonon process to high-field transport phenomena. This finding resolves a long-standing discrepancy regarding the strength of intervalley scattering in GaAs as determined from different experimental methods.

Self-formation of high-field domain in epitaxial ZnO and its suppression in ZnO/MgZnO heterostructure

Microwave noise is used to study high-electric-field electronic properties of ZnO channels with electron densities in the range from 1017 to 1019 cm–3. The strong source of noise is observed to superimpose onto the standard hot-electron noise governed by the hot-electron energy relaxation. At a given current, the excess noise temperature ΔTn increases with the channel length, and values up to and above 10 000 K are reached. The steep dependence ΔTn∝I12 on the current I approximately holds for the longest channels. The source of noise in question is suppressed in ZnO epilayers at high electron densities and in a ZnO/MgZnO heterostructure with two-dimensional electron gas. The observed results are evaluated and discussed in terms of the self-formation of high field domains. The estimated domain voltage Ud increases with the current; the dependence is close to Ud∝I6. The domain self-formation is additionally confirmed by measuring the spectral density of current fluctuations; the usual hot-electron noise turns into shot noise as the current increases. The Fano factor demonstrates an increasing number of nearly ballistic electrons that traverse the self-supporting domain.

Terahertz oscillations in gallium nitride quantum-well channels predicted by hot-electron noise temperature behavior at microwave frequency

The almost periodic streaming motion of accelerated electrons under moderate electric fields coupled with almost periodic emission of longitudinal optical (LO) phonons is studied in a gallium nitride quantum-well—a promising pathway for terahertz (THz) oscillations. The optimal conditions for the LO-phonon-terminated streaming depend, among others, on the density of the electron gas, the low-field electron mobility, the lattice temperature, and the electric field in a very specific way. The present manuscript exploited the electron noise temperature measured at an X band frequency as a marker for the oscillations at THz frequencies. The idea was tested on a deterministic model for a GaN two-dimensional electron gas (2DEG) through calculation of the electron noise temperature spectra in the Langevin approach for the frequency range from 1 GHz to 10 THz. The noise temperature at 10 GHz was found to be in a strong anticorrelation with the THz peaks in the noise temperature spectrum. In particular, a weaker dependence on the applied electric field at 10 GHz implies stronger THz oscillations. In an experiment, the microwave hot-electron noise measurements were carried out for AlGaN/AlN/GaN heterostructures with the 2DEG channel at 10 GHz under pulsed electric field conditions in order to mitigate the effect of Joule heating of the channel. The plateau-like behavior of the noise temperature, in its dependence on the electric field, was obtained for the 2DEG channels with rather low electron densities (2.5×1012 cm−2) in a good agreement with the model. The aforementioned plateau in the electron noise temperature observed at 10 GHz can be used as an indicator for the THz oscillations.

Hot-electron energy relaxation time in Ga-doped ZnO films

Hot-electron energy relaxation time is deduced for Ga-doped ZnO epitaxial layers from pulsed hot-electron noise measurements at room temperature. The relaxation time increases from ∼0.17 ps to ∼1.8 ps when the electron density increases from 1.4 × 1017 cm−3 to 1.3 × 1020 cm−3. A local minimum is resolved near an electron density of 1.4 × 1019 cm−3. The longest energy relaxation time (1.8 ps), observed at the highest electron density, is in good agreement with the published values obtained by optical time-resolved luminescence and absorption experiments. Monte Carlo simulations provide a qualitative interpretation of our observations if hot-phonon accumulation is taken into account. The local minimum of the electron energy relaxation time is explained by the ultrafast plasmon-assisted decay of hot phonons in the vicinity of the plasmon–LO-phonon resonance.

Hot-electron noise properties of graphene-like systems

We study the hot-electron noise properties of two-dimensional materials with a graphene-like energy dispersion under a strong applied electric field which drives the system far from equilibrium. Calculations are based on a Boltzmann--Green-function method within a two-relaxation-time approximation that allows for both inelastic scattering coming from electron-phonon scattering and elastic scattering coming from electron-impurity scattering. The steady-state distribution function is used to calculate the average current and the low-frequency spectral density for current fluctuations (noise) in the nonequilibrium steady-state. We find that as the electric field strength increases, the noise decreases from its equilibrium thermal noise value. This is in contrast with semiconductors with a quadratic energy--wave-vector dispersion where the noise increases in a constant-relaxation-time model with the square of the electric field due to the Joule heating of the electron gas by the electric field. We have also studied these properties for an electronic dispersion with a gap introduced into the Dirac spectrum. The inclusion of the gap in the electronic dispersion causes an initial increase in the noise as a function of external electric field due to the heating of the electron gas for large gap values. At high electric fields, the noise decreases with increasing electric field as in the case of gapless dispersion at higher fields.

Monte-Carlo simulation of microwave noise in n-type InSb

Numerical Monte Carlo calculations of the electron noise temperature dependence on the electric field strength in n-type InSb are presented. It is established that hot electron noise temperature in strongly compensated InSb increases with the increase of electron density due to more intensive electron–electron scattering stimulating delocalization of electrons from the bottom of the conduction band. For low electron density, when the electron–electron scattering is negligibly small, the electron noise temperature is found to become close to the lattice temperature in a wide range of electric field strength in which the electron gas cooling effect takes place. Satisfactory agreement between calculations of the electron noise temperature and available experimental data has been obtained.

Hot-phonon lifetime in Al0.23Ga0.77N/GaN channels

Hot-phonon effects on hot-electron noise and transport are investigated in nominally undoped two-dimensional Al0.23Ga0.77N/GaN channel with electron density of 7.4 × 1012 cm−2. The electrons are subjected to electric field applied in the channel plane. The dependence of noise temperature on supplied electric power yields hot-phonon lifetime of (370 ± 100) fs at low levels of power (<1 nW/electron). Monte Carlo simulation of hot-electron drift velocity with the same lifetime value as a model parameter confirms the experimental findings. The lifetime decreases as the supplied power increases until the values below 50 fs are deduced at high level of power (>10 nW/electron). These values are substantially lower than the plasmon-free lifetime, and the experimental data are interpreted in terms of plasmon-assisted conversion of hot phonons into acoustic phonons and to other vibration modes.

Hot-electron noise features in silicon crystals operating under periodic signals

We study the intrinsic noise in n-type Si crystals operating under high-frequency periodic electric fields. To simulate the dynamics of electrons in the bulk, by taking into account the main details of band structure, scattering processes, as well as heating effects, a Monte Carlo approach is used. The noise properties are investigated by computing the velocity fluctuations correlation function, its spectral density, and the total noise power for different values of the amplitude and frequency of the driving field. We show that the noise features are significantly affected by the electric field amplitude and frequency and discuss their peculiarities in comparison with those exhibited in the static field case. We find the integrated spectral density, i. e. the total noise power, monotonically reducing its value with the increase of the field frequency, for each amplitude of the applied field. These results can be considered a first step towards a full understanding of the physical characteristics of electronic noise in Si devices, driven by periodic electric fields, relevant, for example, for harmonic generation purposes.

Hot-electron noise features in silicon crystals operating under periodic signals

We study the intrinsic noise in n-type Si crystals operating under high-frequency periodic electric fields. To simulate the dynamics of electrons in the bulk, by taking into account the main details of band structure, scattering processes, as well as heating effects, a Monte Carlo approach is used. The noise properties are investigated by computing the velocity fluctuations correlation function, its spectral density, and the total noise power for different values of the amplitude and frequency of the driving field. We show that the noise features are significantly affected by the electric field amplitude and frequency and discuss their peculiarities in comparison with those exhibited in the static field case. We find the integrated spectral density, i. e. the total noise power, monotonically reducing its value with the increase of the field frequency, for each amplitude of the applied field. These results can be considered a first step towards a full understanding of the physical characteristics of electronic noise in Si devices, driven by periodic electric fields, relevant, for example, for harmonic generation purposes.

Noise temperature spectrum of hot electrons in semiconductor superlattices

The small signal response and thermal noise spectra in miniband superlattice are investigated. The properties of hot electron differential mobility, velocity fluctuation, and noise temperature are determined around a stationary condition. The field and frequency dependent drift velocity, electron energy, effective mass, and electron temperature are obtained. At low frequencies, noise temperature increases rapidly with the electric field. Our calculated noise temperatures for miniband superlattice are in good agreement with the experimental results, with the sample thickness estimated to be around 4 μm.

Hot-Electron Transport, Noise and Power Dissipation in GaN Channels at High Density of Electrons

The experimental results on transport, noise, and dissipation of electric power for voltage-biased Si-doped GaN channels are compared with those of Monte Carlo simulation. The measured dissipated power shows a stronger hot-phonon effect than the simulated one. On the other hand, the experimental results on the electron drift velocity at high electric fields show a weaker hot-phonon effect as compared with the simulated one. The misfit can be reduced if a conversion of the friction-active nonequilibrium longitudinal optical phonons into the friction-passive longitudinal optical phonons is considered.

Frequency Influence on the Hot-Electron Noise Reduction in GaAs Operating under Periodic Signals

A Monte Carlo study of the role of the frequency on the hot-electron intrinsic noise reduction in an n-type GaAs bulk driven by two mixed cyclostationary electric fields is presented. Previous numerical results showed the possibility to reduce the diffusion noise under specific wave-mixing conditions. In this work the variations of the noise properties are investigated by computing and integrating the spectral density of the velocity fluctuations. We found that the effect of reduction of the noise level due to the addition of a second field at twice frequency is almost independent of the frequency.

Hot-Electron Transport and Noise in GaN Two-Dimensional Channels for HEMTs

Accumulation of non-equilibrium longitudinal optical (LO) phonons (termed hot phonons) is considered as a possible cause for limitation of frequency of operation of GaN-based high-electron-mobility transistors (HEMTs). The experimental data on noise temperature of hot electrons at a microwave frequency as a function of supplied electric power is used to extract information on hot phonons: the hot-phonon lifetime, the equivalent hot-phonon temperature, the effective occupancy of hot-phonon states involved into electron-LO-phonon interaction. The possible ways for controlling the hot-phonon effect on electron drift velocity through variation of electron density, channel composition, and hot-phonon lifetime are discussed. The expected dependence of hot-electron drift velocity on hot-phonon lifetime is confirmed experimentally. A self-consistent explanation of different frequency behaviour of InP-based and GaN-based HEMTs is obtained from a comparative study of hot-phonon effects.

Hot electron noise in n-type GaAs in crossed electric and magnetic fields

A Monte Carlo analysis of hot electron noise properties of bulk n-type GaAs in crossed electric and magnetic fields is presented. Effects due to the nonparabolicity of the conduction band are properly taken into account by means of a local parabolic approximation. Stochastic properties of electron transport are investigated by computing the velocity autocorrelation function as well as the spectral density of its fluctuations. It is found that these functions are significantly affected by the presence of the magnetic field and exhibit signatures of nonparabolicity and of occurrence of intervalley scattering between nonequivalent valleys. At suitable electric field strengths noise is lowered in a wide range of frequencies with a simultaneous decreasing of its total power.

Hot‐electron microwave noise and power dissipation in AlGaN/AlN/GaN channels for HEMTs

Dependence of hot-electron noise temperature on supplied electric power is measured at room temperature for an AlGaN/AlN/GaN channel with a two-dimensional electron gas (1 × 1013 cm–2). The results are interpreted in an electron-temperature approximation for a 5-subband model with electron-gas degeneracy taken into account. The fitting is obtained when non-equilibrium (hot) longitudinal optical (LO) phonons are taken into account. The estimated effective occupancy of the involved LO-phonon states exceeds the equilibrium one more than 30 times at 2000 K electron temperature. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

High-Frequency Noise Sources in Quantum Wells

Hot-electron noise is investigated for InGaAs and InAs quantum wells containing a two-dimensional electron gas channel in a pulsed electric field applied parallel to the interfaces. Noise sources resulting from hot-electron thermal motion, electron temperature fluctuations, and real-space transfer are observed. The experimental results on hot-electron thermal noise are used to estimate energy relaxation time in the field range where other sources do not play any important role. Measurements of noise anisotropy in the plane of electron confinement are used to discuss real-space-transfer noise. High-frequency noise technique is used to study hot-electron trapping, and trap location in InAlAs/InGaAs/InAlAs heterostructure channels is determined.

Hot-electron energy relaxation, noise, and lattice strain in InGaAs quantum well channels

Energy loss by hot electrons in lattice-matched and strained InGaAs layers is estimated from experimental data on microwave noise obtained for InP-based quantum well channels containing two-dimensional electron gas. A strong correlation of the energy relaxation time and the lattice strain is observed.

Hot-Electron Noise in a GaAs Planar-Doped Barrier Diode: Experiment and Monte Carlo Simulation

Hot-Electron Noise in a GaAs Planar-Doped Barrier Diode: Experiment and Monte Carlo Simulation

Competition of shot noise and hot-electron noise in GaAs planar-doped barrier diode

Microwave noise in GaAs planar-doped barrier diodes is investigated over a wide range of bias. Suppression of shot noise at intermediate densities of current and an onset of hot-electron noise at high densities are evidenced by experimental data and Monte Carlo simulation.