Hot-electron Conditions Research Articles

Hot-electron effects on AlGaAs/InGaAs/GaAs PHEMTs under accelerated DC stresses

The behavior of Schottky gate characteristics before and after hot-electron stress has been a relatively neglected topic. Thus, this paper discussed the effects of hot-electron accelerated stress on the DC characteristics of AlGaAs/InGaAs/GaAs PHEMTs as they relate to Schottky gate characteristics. It also presents studies of reverse Schottky gate characteristics before and after hot-electron stresses, as related to two major mechanisms: (1) the widening of the depletion region under the gate; and (2) the impact of the carriers trapped under the gate. The former induces a larger Schottky barrier height with a smaller reverse leakage current density than the latter, while the latter induces the opposite. Two hot-electron conditions are used to investigate the impact of the hot-electron stress on the gate leakage current. The gate leakage current decreases after a hot-electron stress, due the effect of hot-electron stress on the Schottky diode characteristics. Moreover, improvement in the noise performance is expected, due to the decrease in the gate leakage current. Both pre- and post-stress noise measurements have been done to demonstrate this.

A Drain Avalanche Hot Carrier Lifetime Model for n- and p-Channel MOSFETs

A simple and physical drain avalanche hot carrier lifetime model has been proposed. The model is based on a mechanism of interface trap generation caused by recombination of hot electrons and hot holes. The lifetime is modeled as /spl tau/(I/sub d//W)/sup 2//spl prop/(I/sub sub//I/sub d/)/sup -m/. The formula is different from the conventional /spl tau/I/sub d//W-I/sub sub//I/sub d/ model in that the exponent of I/sub d//W is 2, which results from the assumed mechanism of the two-carrier recombination. It is shown that the mechanism gives a physical basis of the empirical /spl tau/-I/sub sub//W model for NMOSFETs. The proposed model has been validated experimentally both for NMOSFETs and for PMOSFETs. Model parameters extracted from experimental data show that carrier critical energies for creating damage are lower than the interface potential barriers. It is supposed that oxide band edge tailing enables low-energy carriers to create the damage. The channel hot electron condition becomes the worst case in short channel NMOSFETs, because gate voltage dependence of the maximum channel electric field decreases.

Multiple level optimization for high frequency ac mobility in GaAs quantum wells under hot-electron condition

The basic intention of this work is to determine the optimum values of the system parameters of GaAs quantum wells under hot electron condition. The energy loss to LO phonons and the momentum loss through the interaction with LO phonons, deformation acoustic phonons and ionized impurities are incorporated in the calculations. The small-signal ac mobility is calculated on the basis of a heated drifted Fermi–Dirac distribution function for getting the desired ac mobility at a particular dc biasing field. The parameter optimization is done by employing the genetic algorithms to get the desired small-signal ac mobility. This will make feasible the fabrication of a variety of new quantum devices with desired properties.

Application of genetic algorithm to determine the optimized system parameters of GaAs quantum wells for better high-frequency performance under hot electron condition

A soft computing tool, Genetic Algorithm, is employed here to determine the optimized system parameters of GaAs quantum wells for better high-frequency performance under hot electron condition. For a particular DC biasing field, it is possible to predict the optimum values of the system parameters, like electron temperature, channel width, carrier concentration, for realizing a particular high-frequency response characterized by a cutoff frequency, a frequency at which AC mobility falls to 0.707 of its low-frequency value. The cutoff frequency decreases with the rise of both the channel width and the carrier concentration, whereas it enhances with the increase of lattice temperature and is found to be higher at higher DC biasing fields.

Hot carrier degradation for narrow width MOSFET with shallow trench isolation

We have investigated the hot carrier reliability characteristics of narrow width MOSFET with shallow trench isolation. In the case of maximum substrate current condition, the lifetime of nMOSFET is slightly degraded by decreasing the device width. However, a significant degradation of device lifetime of the narrow width device was observed under channel hot electron condition ( V g= V d). In the case of pMOSFET, we also found enhanced degradation of narrow width device under channel hot electron condition. Enhanced degradation of MOSFETs can be explained by both the current crowding and enhanced charge trapping at the shallow trench isolation edge. Considering pass transistor in DRAM cell, the degradation of lifetime for narrow width device under high gate bias condition causes a significant impact on circuit reliability.

Thermometer for the 2D Electron Gas using 1D Thermopower

We measure the temperature of a 2D electron gas in GaAs from the thermopower of a one-dimensional ballistic constriction, using the Mott relation to confirm the calibration from the electrical conductance. Under hot electron conditions, this technique shows that the power loss by the electrons follows a $T^5$ dependence in the Gruneisen-Bloch regime, as predicted for acoustic phonon emission with a screened piezoelectric interaction. An independent measurement using conventional thermometry based on Shubnikov-de Haas oscillations gives a $T^3$ loss rate; we discuss reasons for this discrepancy.

Low-dimensional electron transport properties in InAs/AlGaSb mesoscopic structures

We report on the successful fabrication and electrical transport properties of single quantum wires fabricated by using InAs/AlGaSb heterostructures. Magnetotransport and high electric field characteristics have been measured on the various size of quantum wires. From comparison with the channel length-dependence of I–V characteristics of the different size quantum wires, we try to develop a comprehensive understanding on the quasi-one dimensional electron transport in InAs from the nearly ballistic regime to the hot electron condition. The fabrication and characteristics of superconducting weak link InAs/Pb:In devices are also reported. The modulation of differential conductivity has been observed by the gate bias voltage between the superconducting Pb–In contacts.

Numerical solution of coupled steady-state hot-phonon-hot-electron Boltzmann equations in InP.

A matrix method for the numerical determination of steady-state hot-phonon and nondegenerate hot-electron distribution functions is presented. The coupled Boltzmann equations for the longitudinal-optical phonons and for the electrons, in the \ensuremath{\Gamma} and L valleys of III-V semiconductor compounds, are iteratively solved with high accuracy under typical hot-electron conditions. The phonon distribution is shown to be significantly disturbed from thermal equilibrium. In turn, nonequilibrium phonons induce a substantial disturbance of the hot-electron distribution. Computations are performed for InP at 300 K, taking into account all relevant scattering mechanisms. It turns out that the electron transport parameters are strongly affected in the field range from 0 to 10 kV/cm: the drift velocity is increased by about 42% at 2 kV/cm and the Ohmic mobility by 37%. These effects are shown to be due to the drag and reduced cooling of the carriers by the nonequilibrium LO phonons.

Hot magneto-phonon and electro-phonon resonances in heterostructures

When the energy separation of two quantum levels equals the energy of an LO phonon, resonant interaction occurs which leads to an enhancement of the scattering rate and consequently to a suppression of the conductivity. This effect is called magneto-phonon resonance (MPR) when the resonant scattering occurs between two Landau levels, and electro-phonon resonance (EPR) when the scattering occurs between two electrical subbands. The authors discuss both effects in GaAs/AlxGa1-xAs heterostructures under hot-electron conditions. The influence of the heating of the electrons on the resonant condition and the amplitude of the effect is studied.

Harmonic generation in II‐VI compound semiconductors under hot electron condition

AbstractThe second harmonic generation efficiency has been calculated in a number of II‐VI‐compound semiconductors under high‐field condition by approximating the velocity‐field characteristics by a power‐series relation. It is found that the second harmonic generation efficiency is much higher in these materials than in the elemental or IIIV compound semiconductors. Also, because the carrier relaxation times are lower in these materials, they can be used for efficient harmonic power generation in the infrared‐ and millimeter‐wavelength ranges.

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.

Velocity-fluctuation noise in semiconductor layers and in MESFET channels under hot-electron conditions

The power spectral density of velocity-fluctuation noise in a semiconductor layer, or in the channel of a MESFET device, in the presence of a biasing electric field creating hot-eletron conditions, is calculated from the nonlinear dc current-voltage characteristic of the semiconductor existing under those conditions, by the use of Gupta's nonlinear thermal noise theorem. The calculated results are shown to agree with measured noise temperatures for a variety of devices, at microwave frequencies and at moderately high electric fields. An empirical result relating the excess noise temperature in GaAs to the electric field is proposed.

Non-equilibrium cyclotron resonances in GaInAs/InP two-dimensional electron gas

Non-equilibrium cyclotron resonances under hot electron conditions are studied for a two-dimensional electron gas in GaInAs/InP heterojunctions. Several novel peaks observed in the higher field are attributed to the transitions between higher-order Landau subbands. Their field splittings from the fundamental transitions are consistent with those of equilibrium resonances and the 2DEG splittings yield larger values than those in GaInAs bulk electrons. This is in contrast to the result in the GaAs/AlGaAs system. Calculations taking into account non-parabolicity and polaron pinning effect explain only a part of the splittings. If the non-parabolicity is assumed to remain constant in the heterojunction, the experimental results would then suggest enhanced polaron coupling in this system.

Longitudinal Magnetophonon Resonance inn-Type InP in Ohmic and Hot Electron Region

Longitudinal magnetophonon resonance in epitaxially grown n-type InP was studied in Ohmic and hot electron conditions using pulsed high magnetic fields up to 30 T. In the temperature range between 140 and 240 K, it was found that in the Ohmic region the longitudinal magnetophonon peaks with integer harmonic numbers showed a considerable phase shift whereas those with half-integer harmonic numbers are in good agreement with the theoretically predicted positions. In hot electron conditions at low temperatures 10-40 K, new structure was observed in high magnetic field range.

Nonlinear FIR magnetoabsorption under laser-induced hot electron conditions in semiconductors

Nonlinear FIR magnetoabsorption under laser-induced hot electron conditions in semiconductors

Polaron cyclotron resonance in n-CdTe and n-InP

The interaction of electrons and polar-optical phonons is investigated for CdTe and InP in cylotron resonance (CR) emission and absorption experiments. Under hot electron conditions three different Landau level transitions are observed. From the positions of the fundamental transition and the CR line splittings the nonparabolicity and the polaron contribution to the effective mass are analysed using a variational approach for the polaron shifts. The bare band edge masses and the polaron coupling constants are determined to be m ∗ 0 = 0.0900±0.0005 , α=0.35+-0.03 for CdTe and m ∗ 0 = 0.0765±0.0005 , α=0.15±0.01 for InP.

Magnetophonon resonance recombination of hot carriers with emission of two TA-phonons in LPE-HgTe

Magnetophonon oscillations of longitudinal magnetoresistance of LPE-HgTe were investigated at 4.2 K under hot electron condition by using a second derivative method. Oscillations with 3–5 peaks were observed in 2–9T under electric field of about 1–4V cm -1. These peaks are interpreted as the first observation of magnetophonon resonance recombination of hot carriers accompanied by two TA-phonon emission. It is deduced for the first time that at low temperatures TA-phonon density of states has two peaks at 2.6 and 3.1 meV respectively.

Ga0.47 In0.53 As—The material for high-speed devices

Electron transport properties of Ga0.47In0.53As are reviewed. The available physical constants of the material and results on electron mobility in bulk materials, 2deg systems and under hot-electron conditions are presented. Applications of the material in the construction offet’s and photo-conductive detectors are briefly discussed.

Cyclotron resonance study of polarons in GaAs

Cyclotron resonance absorption and emission experiments have been performed under hot-electron conditions. Four different Landau-level transitions are observed. From the splitting of the cyclotron-resonance lines, polaron effects are determined. Different polaron theories are applied and their validity is discussed. An accurate treatment of polaron effects is found to be necessary for the determination of the band-edge effective mass, which is determined to be ${m}_{0}^{*}=0.0650m$.

Cyclotron resonance studies of polarons and screening effects in GaAs

Polaron effects are studied in bulk n-GaAs by cyclotron resonance measurements under hot electron conditions. Good agreement between calculations and experiments is obtained. The Fröhlich parameter determined is close to the literature value. An accurate treatment of polaron effects is necessary for the determination of the bandedge effective mass. In GaAsGa xAl 1−xAs heterojunctions the influence of the free carrier concentration on the cyclotron resonance linewidth is investigated and screening is found to be ineffective. Polaron effects are weaker than determined in bulk samples.