Hot-electron Drift Velocity Research Articles

Determination of hot-electron drift velocity in (Be)ZnMgO/ZnO 2DEG channels

Recent experimental study of electron transport in ZnO/ZnMgO and BeZnMgO/ZnO heterostructures containing two-dimensional electron gas (2DEG) channels of two polarities is reported where electrons are accelerated and become hot by a pulsed electric field. The measurements with electrical pulses ranging from 2 ns to 10 ns in duration ensure the control of self-heating effect. Electron transport in the ZnO 2DEG channels located in ZnO layers at the ZnMgO or BeZnMgO barrier or in ZnO 3DEG channels is treated mainly in terms of drift velocity. The highest values of 1.3 × 107 cm/s at 360 kV/cm, 2.0 × 107 cm/s at 270 kV/cm, and 2.5 × 107 cm/s and 320 kV/cm, respectively, are attained and explained by emphasizing the effect of hot phonons.

Hot electron transport in wurtzite-GaN: effects of temperature and doping concentration

The hot electron transport in wurtzite phase gallium nitride (Wz-GaN) has been studied in this paper. An analytical expression of electron drift velocity under the condition of impact ionization has been developed by considering all major scattering mechanisms such as deformation potential acoustic phonon scattering, piezoelectric acoustic phonon scattering, optical phonon scattering, electron-electron scattering and ionizing scattering. Numerical calculations show that electron drift velocity in Wz-GaN saturates at 1.44 × 105 m/s at room temperature for the electron concentration of 1022 m−3. The effects of temperature and doping concentration on the hot electron drift velocity in Wz-GaN have also been studied. Results show that the saturation electron drift velocity varies from 1.91 × 105–0.77 × 105 m/s for the change in temperature within the range of 10–1000 K, for the electron concentration of 1022 m−3; whereas the same varies from 1.44 × 105–0.91 × 105 m/s at 300 K for the variation in the electron concentration within the range of 1022–1025 m−3. The numerically calculated results have been compared with the Monte Carlo simulated results and experimental data reported earlier, and those are found to be in good agreement.

Hot Electrons in InxGa1–xN and InxAl1–xN Binary Solid Solutions

The nonlinear field dependences of the hot electron drift velocity have been calculated by means of numerical solution of the Boltzman kinetic equation in two families of nitride semiconductor solid solutions: InxGa1–xN and InxAl1–xN. The calculations have been carried out in the electric field up to 30 kV/cm at lattice temperatures of 77 and 300 K, and for electron concentrations of 1 × 1018 and 1 × 1019 cm–3. In the calculations, the composition x has been taken as 0, 0.25, 0.5, 0.75, and 1 for both alloys.

Electron transport in a coupled GaN/AlN/GaN channel of nitride HFET

Longitudinal hot-electron transport is investigated for the alloy-free AlGaN/AlN/{GaN/AlN/GaN} heterostructure at electric fields up to 380 kV/cm. The structure featured a coupled channel with a camelback electron density profile. The hot-electron drift velocity in the coupled channel is estimated as ~1.5×107 cm/s and is ~50% higher as compared with the standard AlN-spacer GaN 2DEG channel. The HFET with the pristine 2DEG density of 1.75×1013 cm–2 confined in the coupled channel demonstrates the optimal frequency performance in terms of electron velocity at a relatively low gate bias of VGS = –1.75 V. These results are consistent with the ultra-fast decay of hot phonons.

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 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.

Electron Transport and Microwave Noise in MBE- and MOCVD-Grown AlGaN/AlN/GaN

Microwave noise temperature, current, and dissipated power were investigated at room temperature in undoped AlGaN/AlN/GaN channels grown by molecular beam epitaxy and metal-organic compound vapour decomposition techniques. Samples with essentially the same electron density (1× 10 cm−2) and low-field mobility (1150 cm/(V s)) demonstrated considerably different behaviour at high electric fields. The effective hot-phonon lifetime, 300 fs and 1000 fs, respectively, was estimated for molecular beam epitaxy and metal-organic compound vapour decomposition samples. The expected anti-correlation of hot-phonon lifetime and hot-electron drift velocity was confirmed experimentally.

Effect of alloy scattering on the longitudinal hot electron drift velocity in n-Hg0.8Cd0.2Te in the extreme-quantum-limit magnetic fields at low temperatures

Longitudinal hot electron drift velocity in n-Hg0.8Cd0.2Te in the extreme quantum limit has been investigated at low temperatures using displaced Maxwellian approximation. The model includes various complexities such as band nonparabolicity, quantum screening due to magnetic quantization, and Landau level broadening due to impurity fluctuations. The influence of alloy scattering on the drift velocity has been examined. The field dependences of hot electron drift velocity in n-Hg0.8Cd0.2Te have also been studied.

Theoretical and experimental investigation of the drift velocity in AlGaAs/GaAs heterostructures

The drift velocity of hot electrons in AlGaAs/GaAs heterostructures is measured at different temperatures by a pulsed I-V technique up to electric fields of 1.2 kV/cm. The experimental results are compared with theoretical drift velocities deduced from the Boltzmann integral equation and a balance equation method. The calculations are carried out with selfconsistent and Stern–Howard wave functions taking into account polar optical phonon and ionized impurity scattering as well as electron-electron collisions. At low field strengths both theoretical methods lead to drift velocities which are in good agreement with the experimental data. It is shown that for higher lattice temperatures and higher electric field strengths intersubband scattering has to be taken into account in the theoretical models.

Numerical investigation of the intersubband and intervalley drift velocity by the Boltzmann integral equation method

The influence of intersubband and intervalley scattering onto the drift velocity of hot 2D electrons in n-GaAs quantum wells and heterostructures is investigated numerically for the first time by means of the Boltzmann integral equation method. The dependence of the subband energy separation onto the drift velocity is analyzed systematically. The drift velocity in quantum wells having a thickness larger than 100 Å is found to be significantly reduced by intersubband transitions if the external electric field exceeds 1 kV/cm.

Measurement of the hot-electron conductivity in semiconductors using ultrafast electric pulses

Semiconductor response to ultrafast electric pulses was investigated both theoretically and experimentally. The possibilities for hot-electron drift velocity estimation from a pulsed electric conductivity measurement were analysed. An optoelectronic arrangement with time resolution of 20 ps was used to perform such measurements on then-InSb andn-InAs single crystals. Negative differential mobility (n.d.m.) was observed in both semiconductors at high electric fields.

Theoretical analysis of the intrasubband drift velocity of hot electrons in n-GaAs quantum wells

The drift velocity of hot electrons in an n-GaAs quantum well is calculated with the exact distribution function deduced from the Boltzmann integral equation. The interaction of the charge carriers with surface and bulk polar optical phonons and ionized impurities is considered in the calculation. The influence of intercarrier collisions as well as the quantum-well width on the distribution function and on the drift velocity is analyzed systematically. The theoretical results are compared with recent experimental data deduced from pulsed Hall measurements.

The effect of electrostatic interactions on hot electron transport in n-GaAs

Hot electron transport in bulk n-GaAs is investigated in a three dimensional numerical simulation. An emphasis is placed on understanding the effect of the electrostatic interaction and, in particular, that of the ionized impurity scattering on drift velocity vs electric field characteristics. In order to account for the spatial correlations between electrons and scattering centers, the numerical model combines molecular dynamics and Monte Carlo techniques. A major result is that the impurities enhance the drift velocity of hot electrons. This emphasizes the inappropriateness of the concept of a phenomenological mean free flight time when the interaction potential is long range. An explanation of the effect is proposed which applies to a general multi-valley semiconductor; and the model is compared to the traditional Brooks-Herring treatment of electron-ionized impurity scattering.

Hot-electron conduction in Hg0.8Cd0.2Te in the extreme magnetic quantum limit at low temperatures

A theoretical analysis of hot-electron transport in narrow-gap semiconductors under a large magnetic field is developed at low temperatures. The energy relaxation time and the electric-field dependence of the drift velocity of hot electrons in Hg0.8Cd0.2Te at 1.5 K in the extreme quantum limit, i.e., when all the electrons occupy the lowest Landau subband, are calculated. The model includes scattering by the acoustic phonons and other complexities such as the band nonparabolicity, free-carrier screening, nonequipartition of phonons, and the level broadening due to electron-impurity interactions. The theoretical results are compared with the experimental data on the energy relaxation time in Hg0.8Cd0.2Te for magnetic flux densities of 4 and 6 T. When the equilibrium phonon distribution is considered, the theoretical values are found to be several times less than the experimental values. The discrepancy is attributed to the nonequilibrium phonons or ‘‘hot phonons’’ that exist under hot-electron conditions. Including the hot-phonon effects, the theoretical results are in satisfactory agreement with the experimental data, giving a reasonable estimate of the phonon life time. The model has been applied to calculate the electric field dependence of the drift velocity of hot electrons in Hg0.8Cd0.2Te at 1.5 K in the extreme quantum limit by assuming scattering by the nonequilibrium acoustic phonons and ionized impurities, and a satisfactory agreement with the experimental results is obtained.

Monte Carlo calculations of transport parameters of one-dimensional hot electrons in quantum-well wires.

Monte Carlo calculations of hot-electron drift velocity, average energy, and diffusion coefficient are reported for the one-dimensional electron gas in a GaAs quantum-well wire of square cross section with side length L. Electron scattering by acoustic and longitudinal polar optic phonons is included. The transport parameters are found to rise more rapidly with electric field for L=160 A\r{} than for L=40 A\r{}, particularly at a lower ambient temperature. Einstein's relationship is shown to underestimate the hot-electron diffusivity for r=160 \AA{}.

Electric field dependence of the hot-electron drift velocity in Hg 0.8Cd 0.2Te under magnetic quantisation at low temperatures

The electric-field dependence of the drift velocity of hot electrons in Hg 0.8Cd 0.2Te at a lattice temperature of 1.5 K is studied theoretically in the extreme magnetic quantum limit considering electron scattering by acoustic phonons and ionised impurities. Band non-parabolicity, free carrier screening, non-equipartition and non-equilibrium condition of acoustic phonons, and Landau level broadening due to electron-impurity interactions are included in the calculations. The agreement with recent experimental data is found to be satisfactory.

Hot-electron drift velocity in III?V semiconductors under the condition of impact ionization

A calculation has been carried out for the drift velocity of electrons in the highfield region under the condition of impact ionization in III–V semiconductor compounds.

High frequency application of hot electrons in superlattices

Abstract The properties of lateral surface superlattices (LSSLs) as high frequency devices are investigated. The two most interesting possibilities are the use of a negative differential mobility as the basis for oscillators and amplifiers similar in nature to those obtained using Gunn devices, and the possible direct interaction between high frequency electric fields and electrons undergoing Bloch oscillations. Both of these possibilties will be discussed. The possible negative resistance device applications are investigated using standard computer simulations of Gunn-like device elements. First, Monte Carlo techniques are used to estimate the hot electron drift velocity and diffusion coefficients of a prototype LSSL. These transport coefficients are then incorporated into a device simulation. By using this simulation we illustrate the possible advantages of these structures over standard GaAs Gunn devices. These advantages stem from the substantially lower diffusion coefficients, the absence of a high field saturated drift velocity and the lack of any intervalley transfer processes. The possibility that an incident high frequency electric field can interact with electrons undergoing Bloch oscillations has been previously noted. Here we extend these discussions to include scattering mechanisms by including time-varying fields in a Monte carlo simulation of hot electron transport in a LSSL.

Drift Velocity of Hot Electrons in Liquid Ar, Kr, and Xe

The drift velocity of hot electrons in liquid Ar, Kr, and Xe near their triple points ia studied using a Cohen-Lekner equation in which an inelastic depolarized electron scattering process is newly considered. The saturation of the drift velocity at the high field strength is appropriately explained. The magnitude and onset energy of the effective inelastic cross section are compared with the experimental data of inelastic light scattering spectra.

Negative differential mobility in PbTe and PbSnTe at high electric fields

Monte Carlo calculations of hot-electron drift velocity in PbTe and Pb 0.8Sn 0.2Te at 77 K are reported. The relevant scattering mechanisms together with band-structure nonparabolicity and anisotropy are included in the calculations. A negative differential mobility (NDM) does not appear when the electrons are assumed to remain confined within the L valleys of the conduction band. On the contrary, allowing for electron transfer into the W valleys and taking suitable values of the parameters related to these valleys, an NDM appears and the threshold field for the same agrees well with the experimental data. Alloy scattering in PbSnTe is found to reduce the NDM.