Hot Electron Drift 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.

Broadening the IF Band of a THz Hot-Electron Bolometer Mixer by Using a Magnetic Thin Film

To expand the intermediate frequency (IF) band and improve the sensitivity of a hot-electron bolometer mixer (HEBM), we proposed and examined a new HEBM structure using a magnetic thin film. We found that it was possible to suppress the superconductivity of the 5-nm-thick niobium nitride (NbN) thin film by the addition of a 1.8-nm-thick nickel (Ni) thin film. It was also confirmed that the superconductivity disappeared in the Au (70 nm)/Ni (1.8 nm)/NbN (5 nm) trilayer for forming the electrodes of the HEBM. By using the magnetic thin film for the electrodes, we suggested that the superconductivity of the HEBM strip would be affected and that hot spots would be formed near the electrodes. This approach is effective for shortening the hot-electron drift length and will lead to the expansion of the IF bandwidth. We think that the new structure lowers the required local oscillator power and improves the HEBM sensitivity by suppressing the proximity effect under the electrode. The IF bandwidth of the fabricated Ni-HEBMs was evaluated at 1.9 THz. We confirmed that the IF bandwidth expands, and the evaluated bandwidths were in the range of 5.1–5.7 GHz at 4 K. Ni-HEBMs with 0.1-μm strip length were also fabricated and evaluated. The IF bandwidth was about 6.9 GHz at 4 K.

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.

Statistical analysis of storm-time near-Earth current systems

Abstract. Currents from the Hot Electron and Ion Drift Integrator (HEIDI) inner magnetospheric model results for all of the 90 intense storms (disturbance storm-time (Dst) minimum < −100 nT) from solar cycle 23 (1996–2005) are calculated, presented, and analyzed. We have categorized these currents into the various systems that exist in near-Earth space, specifically the eastward and westward symmetric ring current, the partial ring current, the banana current, and the tail current. The current results from each run set are combined by a normalized superposed epoch analysis technique that scales the timeline of each phase of each storm before summing the results. It is found that there is a systematic ordering to the current systems, with the asymmetric current systems peaking during storm main phase (tail current rising first, then the banana current, followed by the partial ring current) and the symmetric current systems peaking during the early recovery phase (westward and eastward symmetric ring current having simultaneous maxima). The median and mean peak amplitudes for the current systems ranged from 1 to 3 MA, depending on the setup configuration used in HEIDI, except for the eastward symmetric ring current, for which the mean never exceeded 0.3 MA for any HEIDI setup. The self-consistent electric field description in HEIDI yielded larger tail and banana currents than the Volland–Stern electric field, while the partial and symmetric ring currents had similar peak values between the two applied electric field models.

Statistical analysis of the geomagnetic response to different solar wind drivers and the dependence on storm intensity

AbstractGeomagnetic storms start with activity on the Sun that causes propagation of magnetized plasma structures in the solar wind. The type of solar activity is used to classify the plasma structures as being either interplanetary coronal mass ejection (ICME) or corotating interaction region (CIR) driven. The ICME‐driven events are further classified as either magnetic cloud (MC) driven or sheath (SH) driven by the geoeffective structure responsible for the peak of the storm. The geoeffective solar wind flow then interacts with the magnetosphere producing a disturbance in near‐Earth space. It is commonly believed that a SH‐driven event behaves more like a CIR‐driven event than a MC‐driven event; however, in our analysis this is not the case. In this study, geomagnetic storms are investigated statistically with respect to the solar wind driver and the intensity of the events. We use the Hot Electron and Ion Drift Integrator (HEIDI) model to simulate the inner magnetospheric hot ion population during all of the storms classified as intense (Dstmin ≤ −100 nT) within solar cycle 23 (1996–2005). HEIDI is configured four different ways using either the Volland‐Stern or self‐consistent electric field and either event‐based Los Alamos National Laboratory (LANL) magnetospheric plasma analyzer (MPA) data or a reanalyzed lower resolution version of the data that provides spatial resolution. Presenting the simulation results, geomagnetic data, and solar wind data along a normalized epoch timeline shows the average behavior throughout a typical storm of each classification. The error along the epoch timeline for each HEIDI configuration is used to rate the model's performance. We also subgrouped the storms based on the magnitude of the minimum Dst. We found that typically the LANL MPA data provide the best outer boundary condition. Additionally, the self‐consistent electric field better reproduces SH‐ and MC‐driven events throughout most of the storm timeline, but the Volland‐Stern electric field better reproduces CIR‐driven events. Contrary to what we expect, examination of the HEIDI model results and solar wind data shows that SH‐driven events behave more like MC‐driven events than CIR‐driven storms.

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.

Is the storm time response of the inner magnetospheric hot ions universally similar or driver dependent?

The Hot Electron and Ion Drift Integrator (HEIDI) model was used to simulate all of the intense storms (Dstmin &lt; −100 nT) from solar cycle 23 (1996–2005). These storms were classified according to their heliospheric driving structure, namely, either an interplanetary coronal mass ejection (ICME) or a corotating interaction region and its trailing high‐speed stream (CIR/HSS). Five different HEIDI input combinations were used to create a large collection of numerical results, varying the plasma outer boundary condition and electric field description in the model. Statistical data‐model analyses were conducted on the total energy content, yielding error estimates on the correlation coefficients and root‐mean‐square error values for each run set. The accuracy of each run set depends on the method of comparison and classification of the driver. For the correlation coefficients, the simulations using a local‐time‐dependent outer boundary condition were consistently better than those using a local‐time‐averaged (but high‐time‐resolution) nightside boundary condition, with the simplistic electric field being better than the self‐consistent field description. For the root‐mean‐square error, the results are less conclusive. For the CIR/HSS‐driven storms, those with the high‐time‐resolution boundary condition were systematically better than those with the local‐time‐dependent (but lower‐time‐resolution) boundary condition. For the ICME‐driven storms, those run sets employing the self‐consistent electric field calculation were systematically better than those using the simplistic electric field. The implication, therefore, is that the inner magnetospheric physical response to strong driving is, at least to some degree, fundamentally different depending on the heliospheric structure impacting geospace. Specifically, for an accurate SYMH* comparison, it is found that CIR/HSS events respond strongly to transient spikes in the plasma outer boundary condition, while ICME passages exhibit a more highly structured electric field.

Dayside midlatitude ionospheric response to storm time electric fields: A case study for 7 September 2002

[1] With the storm of 7–8 September 2002 as a study case, we demonstrate that an ionospheric model driven by a suitable storm time convection electric field can reproduce the F region dayside density enhancements associated with the ionospheric storm positive phase. The ionospheric model in this case is the Utah State University Time Dependent Ionospheric Model (TDIM); the electric field model is the University of Michigan's Hot Electron and Ion Drift Integrator (HEIDI). Extensive ground truth is available throughout the study period from two independent sources: ground-based vertical TEC and ionosonde stations; our simulation results are in good agreement with these observations. We address the question of what is the source of the high-density plasma that is seen during the positive storm phase and show that in this case a magnetospheric electric field with an eastward component that penetrates to midlatitudes increases local production on the dayside to a degree that is sufficient to account for the storm time density increases that have been observed.

CIR versus CME drivers of the ring current during intense magnetic storms

Ninety intense magnetic storms (minimum Dst value of less than −100 nT) from solar cycle 23 (1996–2005) were simulated using the hot electron and ion drift integrator (HEIDI) model. All 90 storm intervals were run with several electric fields and nightside plasma boundary conditions (five run sets). Storms were classified according to their solar wind driver, including corotating interaction regions (CIRs) and interplanetary coronal mass ejections (ICMEs). Data-model comparisons were made against the observed Dst index (specifically, Dst*) and dayside hot-ion measurements from geosynchronous orbiting spacecraft. It is found that the data-model goodness-of-fit values are different for CIR-driven storms relative to ICME-driven storms. The results are also different for the same storm category for different boundary conditions. None of the CIR-driven events was overpredicted by HEIDI, while the dayside comparisons were comparable for the different drivers. The results imply that the outer magnetosphere is responding differently to the two kinds of solar wind drivers, even though the resulting storm size might be similar. That is, for ICME-driven events, magnetospheric currents inside of geosynchronous orbit dominate the Dst perturbation, while for CIR-driven events, currents outside of this boundary have a systematically larger contribution.

Ring current simulations of the 90 intense storms during solar cycle 23

All of the intense magnetic storms (minimum Dst value of &lt;−100 nT) from solar cycle 23 (1996–2005) were simulated using the hot electron and ion drift integrator (HEIDI) model. The simulations were run using a Kp‐driven shielded Volland‐Stern electric field, static dipole magnetic field, and nightside plasma data from instruments on the Los Alamos geosynchronous satellites. Of the 90 events, 79 had acceptable plasma boundary condition coverage (with main phase data gaps of 4 h or less) and are included in the analysis. Storms were classified according to their solar wind driver, and means and correlations were examined. It is found that for this model configuration, the HEIDI model was able to best reproduce the Dst time series for sheath‐driven events with an average minimum Dst* from the simulations at or below the observed minimum Dst* value. CIR‐driven events were the least reproducible class of storms, with simulated minimum Dst* values typically only half to two thirds of the observed minimum value. In general, there was a strong correlation between the observed and modeled minimums of Dst* and essentially no correlation between the observed minimum Dst* and the modeled‐to‐observed Dst* ratio. This implies that the size of the eventual storm is not a good indicator of whether this version of HEIDI will be able to accurately reproduce it; rather, a Kp‐driven HEIDI simulation is consistently on the low side of predicting storm intensity, except for sheath‐driven events.

An explanation for high‐frequency broadband electrostatic noise in the Earth's magnetosphere

A parametric study of high‐frequency nonlinear electrostatic oscillations in a magnetized plasma consisting of hot electrons, cool electrons, and cool ions has been conducted. The fluid equations have been used for each species, and the coupled system of differential equations in the rest frame of the propagating wave have been numerically solved to yield the electric field for parameters characteristic of the auroral region. The effect of the initial driving amplitude, cold and hot electron densities, propagation angle, hot electron drift, and cool electron and cool ion temperatures on the electric field structures have been investigated and, in particular, the frequency and the type of electric field structure (sinusoidal, sawtooth, or spiky). The initial driving amplitude as well as the cold and hot electron densities are shown to affect the nature (sinusoidal, sawtooth, or spiky) of the waveforms, with a transition from linear sinusoidal waveforms for low initial driving amplitude, to spiky, nonlinear waveforms for larger values of the initial driving amplitude. In addition, the drifts of the species are shown to play a crucial role in the periods of the waveforms, while the temperatures of the electron species are also shown to vary the periods of the waveforms but not as much as in the case of the drifts of the species. The results show a strong resemblance to satellite observations of the different types of broadband electrostatic noise reported, which are nonlinear, spiky structures of varying amplitude and period.

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.

Excitation of the centrifugally driven interchange instability in a plasma confined by a magnetic dipole

The centrifugally driven electrostatic interchange instability is excited for the first time in a laboratory magnetoplasma. The plasma is confined by a dipole magnetic field, and the instability is excited when an equatorial mesh is biased to induce a radial current that creates rapid axisymmetric plasma rotation. The observed instabilities appear quasicoherent in the lab frame of reference; they have global radial mode structures and low azimuthal mode numbers, and they are modified by the presence of energetic, magnetically confined electrons. The mode structure is measured using a multiprobe correlation technique as well as a novel 96-point polar imaging diagnostic which measures particle flux along field lines that map to the pole. Interchange instabilities caused by hot electron pressure are simultaneously observed at the hot electron drift frequency. Adjusting the hot electron fraction α modifies the stability as well as the structures of the centrifugally driven modes. In the presence of larger fractions of energetic electrons, m=1 is observed to be the dominant mode. For faster rotating plasmas containing fewer energetic electrons, m=2 dominates. Results from a self-consistent nonlinear simulation reproduce the measured mode structures in both regimes. The low azimuthal mode numbers seen in the experiment and simulation can also be interpreted with a local, linear dispersion relation of the electrostatic interchange instability. Drift resonant hot electrons give the instability a real frequency, inducing stabilizing ion polarization currents that preferentially suppress high-m modes.

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.

Does a Doppler shift in the plasmon frequency have to be accounted when evaluating the role of electron–plasmon scattering in gallium arsenide?

We study the effect of a Doppler shift in the plasmon frequency, which arises due to hot electron drift on electron–plasmon scattering rates in GaAs. We show that one must take the account of the Doppler shift when simulating the hot-electron transport in high-purity GaAs.

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.

Oxygen Ion Defect Generation in Insulated‐Gate Field‐Effect Transistors and X‐Radiation Susceptibility of Ion‐Damaged Gate Insulators

In the present paper, the residual electrical effects, before and after postmetal annealing, on insulated gate field‐effect transistor (IGFET) device characteristics due to implantation of oxygen at a dose of 1015 cm−2 into 36‐nm‐thick gate insulators following their growth have been studied. The primary defects detected via optically assisted injection of electrons into the gate insulators of the damaged IGFETs were neutral electron traps (NETs), present in concentrations as high as. Secondary types of defects found appear to be fixed negative charge (FNC), approximately in the worst case, and a smaller amount of fixed positive charge (FPC), less than 1010 cm−2 in the worst case. It is not surprising (unlike the case for silicon implantation under similar conditions) that a smaller number of defects is generated by oxygen implanted into gate insulators following its growth, since the device is subjected to a series of high‐temperature processing steps after the implantation. These high‐temperature processes appear to result in the redistribution and/or volatilization of most of the excess oxygen atoms; volatilization of silicon, on the other hand, is much less likely. Similar to what was observed with silicon‐implanted gate insulators, it was found that these defects could not be removed by employing conventional postmetal annealing (PMA) conditions in forming gas (10% , 90% ) at 400°C for 30 min. The defects created by ion implantation appear to be quite different from those created by x‐ray or electron irradiation, where large quantities of FPCs and NETs are generated, which can be annealed in PMA cycles. It is found that oxygen‐implanted gate insulators appear to be much more susceptible to x‐ray radiation than unimplanted devices. The residual defects in oxygen‐implanted devices, following x‐ray radiation and subsequent PMA annealing for up to 120 min, were found to be greater than that in unimplanted devices. The results with silicon ions earlier, and oxygen ions now, indicate that if the insulator is damaged by such species during processing, as might occur due to knock‐on from the gate electrode during source/drain formation, unannealable defects will form which would also tend to make the device structure more susceptible to radiation damage in a hostile environment, or to large hot electron drift, accompanying conventional use.

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.