Field Dependence Of Drift Velocity Research Articles

Electric field dependence of the electron drift velocity in n-type InxGa1-xAs1-yBiy epilayer

The effect of Bi incorporation into InxGa1-xAs lattice on the nanosecond pulsed electric field dependence of the drift velocity of electrons in n-type InxGa1-xAs1-yBiy alloys with various doping densities is investigated at room temperature. The electronic band structure of the alloys is calculated by Finite Element Methods (FEM). The electron temperature is determined from analytical modeling of the power dissipation mechanism. The drift velocity of the electrons (vdrift) does not saturate up to 5.4 kV/cm electric field for the lowest doping density sample. The sample is burned out at a higher electric field due to the impact ionization mechanism. However, the vdrift saturates at a high electric field region in the samples with higher doping densities, and the saturation of electric field values of vdrift depends on the doping density for these samples. The highest electron drift mobility (μdrift) is obtained as 6236 cm2/Vs for the sample with the lowest electron density. The heating of the only electrons through the applied electric field is not enough to initiate inter-valley transfer because of scatterings during transport. Hence, the electric field dependence on electron transport occurs only in the central valley. The effect of the scatterings on the electron transport is identified by considering ionized impurity and phonon scatterings.

Monte Carlo simulation of avalanche noise characteristics of type II InAs/GaSb superlattice avalanche photodiodes

A Monte Carlo model, which takes account of the stochastic nature of carrier scattering during transportation, including impact ionization, is presented here. To verify the model, it is used to simulate the field dependent drift velocity of electrons transporting in the bulk InAs material. The results are consistent with the experimental data. Then, the model is applied to type II InAs/GaSb superlattice (SL) avalanche photodiode (APD) structure and the avalanche noise characteristics at 77 K is calculated for different wavelengths. Our results reveal that the long wavelength (LW) APD has a higher excess noise factor (F) than the mid wavelength (MW) counterpart, probably due to the fact that holes in the LW SLs are easier to cause the impact ionization. Generally, the F decreases with increasing the device length, except that the device length is very thin for a LW APD.

Negative Differential Resistance Observation and a New Fitting Model for Electron Drift Velocity in GaN-Based Heterostructures

The aim of this paper is an investigation of electric field-dependent drift velocity characteristics for Al0.3Ga0.7N/AlN/GaN heterostructures without and with in situ Si3N4 passivation. The nanosecond-pulsed current–voltage ( ${I}$ – ${V}$ ) measurements were performed using a 20-ns applied pulse. Electron drift velocity depending on the electric field was obtained from the ${I}$ – ${V}$ measurements. These measurements show that a reduction in peak electron velocity from $\text {2.01} \times \text {10}^{\text {7}}$ to $\text {1.39} \times \text {10}^{\text {7}}$ cm/s after in situ Si3N4 passivation. Also, negative differential resistance regime was observed which begins at lower fields with the implementation of in situ Si3N4 passivation. In our samples, the electric field dependence of drift velocity was measured over 400 kV/cm due to smaller sample lengths. Then, a well-known fitting model was fitted to our experimental results. This fitting model was improved in order to provide an adequate description of the field dependence of drift velocity. It gives reasonable agreement with the experimental drift velocity data up to 475 kV/cm of the electric field and could be used in the device simulators.

Roles of voltage in semi-insulating GaAs photoconductive semiconductor switch**Project supported by the National Natural Science Foundation of China (Grant No. 31470822) and the Advanced Research Foundation of China (Grant Nos. 9140A05030114DZ02068, 9140A07030514DZ02101, and 9140A07010715DZ02001).

An experimental study of leakage current is presented in a semi-insulating (SI) GaAs photoconductive semiconductor switch (PCSS) with voltages up to 5.8 kV (average field is 19.3 kV/cm). The leakage current increases nonlinearly with the bias voltage increasing from 1.2×10 A to 3.6×10 A. Furthermore, the dark resistance, which is characterized as a function of electric field, does not monotonically decrease with the field but displays several distinct regimes. By eliminating the field-dependent drift velocity, the free-electron density n is extracted from the current, and then the critical field for each region of n(E) characteristic of PCSS is obtained. It must be the electric field that provides the free electron with sufficient energy to activate the carrier in the trapped state via multiple physical mechanisms, such as impurity ionization, field-dependent EL2 capture, and impact ionization of donor centers EL10 and EL2. The critical fields calculated from the activation energy of these physical processes accord well with the experimental results. Moreover, agreement between the fitting curve and experimental data of J(E), further confirms that the dark-state characteristics are related to these field-dependent processes. The effects of voltage on SI-GaAs PCSS may give us an insight into its physical mechanism.

On the nature of high field charge transport in reinforced silicone dielectrics: Experiment and simulation

The high field charge injection and transport properties in reinforced silicone dielectrics were investigated by measuring the time-dependent space charge distribution and the current under dc conditions up to the breakdown field and were compared with the properties of other dielectric polymers. It is argued that the energy and spatial distribution of localized electronic states are crucial in determining these properties for polymer dielectrics. Tunneling to localized states likely dominates the charge injection process. A transient transport regime arises due to the relaxation of charge carriers into deep traps at the energy band tails and is successfully verified by a Monte Carlo simulation using the multiple-hopping model. The charge carrier mobility is found to be highly heterogeneous due to the non-uniform trapping. The slow moving electron packet exhibits a negative field dependent drift velocity possibly due to the spatial disorder of traps.

A comparative study of transport properties of monolayer graphene and AlGaN-GaN heterostructure

The electronic transport properties of monolayer graphene are presented with an Ensemble Monte Carlo method where a rejection technique is used to account for the occupancy of the final states after scattering. Acoustic and optic phonon scatterings are considered for intrinsic graphene and in addition, ionized impurity and surface roughness scatterings are considered for the case of dirty graphene. The effect of screening is considered in the ionized impurity scattering of electrons. The time dependence of drift velocity of carriers is obtained where overshoot and undershoot effects are observed for certain values of applied field and material parameters for intrinsic graphene. The field dependence of drift velocity of carriers showed negative differential resistance and disappeared as acoustic scattering becomes dominant for intrinsic graphene. The variation of electron mobility with temperature is calculated for intrinsic (suspended) and dirty monolayer graphene sheets separately and they are compared. These are also compared with the mobility of two dimensional electrons at an AlGaN/GaN heterostructure. It is observed that interface roughness may become very effective in limiting the mobility of electrons in graphene.

Drift velocity of electrons in quantum wells of selectively doped In0.5Ga0.5As/Al x In1 − x As and In0.2Ga0.8As/Al x Ga1 − x As heterostructures in high electric fields

The field dependence of drift velocity of electrons in quantum wells of selectively doped In0.5Ga0.5As/AlxIn1 − xAs and In0.2Ga0.8As/AlxGa1 − xAs heterostructures is calculated by the Monte Carlo method. The influence of varying the molar fraction of Al in the composition of the AlxGa1 − xAs and AlxIn1 − xAs barriers of the quantum well on the mobility and drift velocity of electrons in high electric fields is studied. It is shown that the electron mobility rises as the fraction x of Al in the barrier composition is decreased. The maximum mobility in the In0.5Ga0.5As/In0.8Al0.2As quantum wells exceeds the mobility in a bulk material by a factor of 3. An increase in fraction x of Al in the barrier leads to an increase in the threshold field Eth of intervalley transfer (the Gunn effect). The threshold field is Eth = 16 kV/cm in the In0.5Ga0.5As/Al0.5In0.5As heterostructures and Eth = 10 kV/cm in the In0.2Ga0.8As/Al0.3Ga0.7As heterostructures. In the heterostructures with the lowest electron mobility, Eth = 2–3 kV/cm, which is lower than Eth = 4 kV/cm in bulk InGaAs.

Simulation and optimization of GaN-based metal-oxide-semiconductor high-electron-mobility-transistor using field-dependent drift velocity model

Undoped GaN-based metal-oxide-semiconductor high-electron-mobility-transistors (MOS-HEMTs) with atomic-layer-deposited Al2O3 gate dielectrics are fabricated with gate lengths from 1 μm up to 40 μm. With a two-dimensional numerical simulator, we report simulation results of the GaN-based MOS-HEMTs using field-dependent drift velocity model. A developed model, taking into account polarization-induced charges and defect-induced traps at all of the interfaces and process-related trap levels of bulk traps measured from experiments, is built. The simulated output characteristics are in good agreement with reported experimental data. The effect of the high field at the drain-side gate edge and bulk trap density of GaN on the output performance is discussed in detail for the device optimization. AlGaN/GaN/AlN quantum-well (QW) MOS-HEMTs have been proposed and demonstrated based on numerical simulations. The simulation results also link the current collapse with electrons spreading into the bulk, and confirm that a better electron localization can dramatically reduce the current collapse for the QW-MOS-HEMTs. Due to the large band edge discontinuity and effective quantum confinement of the AlGaN/GaN/AlN quantum well, the parasitic conduction in the bulk is completely eliminated.

Coupled energy-drift and force-balance equations for high-field hot-carrier transport

Coupled energy-drift and force-balance equations that contain a frictional force for the center-of-mass motion of electrons are derived for hot-electron transport under a strong dc electric field. The frictional force is found to be related to the net rate of phonon emission, which takes away the momentum of a phonon from an electron during each phonon-emission event. The net rate of phonon emission is determined by the Boltzmann scattering equation, which depends on the distribution of electrons interacting with phonons. The work done by the frictional force is included into the energy-drift equation for the electron-relative scattering motion and is found to increase the thermal energy of the electrons. The importance of the hot-electron effect in the energy-drift term under a strong dc field is demonstrated in reducing the field-dependent drift velocity and mobility. The Doppler shift in the energy conservation of scattering electrons interacting with impurities and phonons is found to lead to an anisotropic distribution of electrons in the momentum space along the field direction. The importance of this anisotropic distribution is demonstrated through a comparison with the isotropic energy-balance equation, from which we find that defining a state-independent electron temperature becomes impossible. To the leading order, the energy-drift equation is linearized with a distribution function by expanding it into a Fokker-Planck-type equation, along with the expansions of both the force-balance equation and the Boltzmann scattering equation for hot phonons.

Electric field dependence of drift velocity and electron temperature of GaAs/AlGaAs 2DEG in the low electric field region

Experimental and theoretical results on low electric field transport of two-dimensional electron gas (2DEG) in AlGaAs/GaAs high electron mobility transistor (HEMT) channel are reported at lattice temperature T L=1.7 K under zero magnetic field. The electron temperature ( T e) and the drift velocity ( υ d) dependence on the electric field ( F) and the electron density in the 2DEG channel are presented. In addition, the variation of the electron temperature with the drift velocity is obtained. The results are obtained for the electric field in the region of 0.01–100 V/cm and in the electron temperature range of 1.7–60 K. It is shown that the electron temperature of 2DEG is a non-monotonous function of the electric field. The results also indicate that electron heating is seen to occur for the electric field F>0.1 V/cm which corresponds to the electron temperature T e=2 K. A sharp increase in the electron temperature T e and in the drift velocity υ d with the electric field below electron temperature of 40 K is seen. The variation of electron temperature with drift velocity is very slow in the same electron temperature range where acoustic phonon emission due to deformation potential is the dominant energy loss mechanism of electronic system. When F>5 V/cm and T e>40 K, where the optic phonon emission is a dominant relaxation mechanism, the electron temperature changes linearly with electric field and the drift velocity increases very rapidly with electron temperature. Also, the drift velocity starts to saturate in this regime. The experimental results are compared with theoretical results and a good agreement is obtained at the electron temperatures of T e<50 K. Above the electron temperature of 50 K, a disagreement is observed between the experimental and the theoretical results which indicates that additional scattering mechanisms should be taken into account and the accuracy of the assumptions concerning the electrons and phonons made in the theory should be questioned.

Unified quantum approach for the electric field-dependent drift velocity and the diffusion coefficient

Based on the Wannier–Stark picture, a unified microscopic approach for the field-dependent drift velocity and diffusion coefficient is derived. This single-particle theory, which is exact for all finite electric field strengths, is applied to study electro-phonon resonances in superlattices.

Monte Carlo calculation of electron drift characteristics and avalanche noise in bulk InAs

Field dependent drift velocity results are presented for electron transport in bulk indium arsenide (InAs) material based on a Monte Carlo model, which includes an analytical treatment of band-to-band impact ionization. Avalanche multiplication and related excess noise factor (F) are computed as a function of device length and applied voltage. A decrease in F with increases in device length is obtained. The results suggest an inherent utility for InAs-based single-photon avalanche detectors, particularly around the 2 μm region of interest for atmospheric remote sensing applications.

Calculations of hole transport characteristics in bulk GaSb with comparisons to GaAs

Field dependent drift velocity results are presented for hole transport in bulk gallium antimonide material based on a Monte Carlo model which includes energy band warping. Transient drift velocities are demonstrated to be higher than for gallium arsenide. The steady-state characteristics are also shown to be superior. The material appears to have potential for high-speed photodetection.

Field dependence of drift velocity and electron population in satellite valleys in gallium arsenide

We present, for the first time, simple explicit expressions for the drift velocity and the electron population in the many-valley band structure of n-type gallium arsenide. It is shown that all the experimentally observed features could be well explained if mean-free-path values of 150 nm and 700 nm in the two sets of valleys are assumed. It is indicated that the mobilities of high-mobility valleys are rapidly degraded with the increase in the electric field. The novel results so obtained could be usefully applied in the design and development of semiconducting devices with two or more energy level structures.

High‐field transport and low‐field mobility in tellurium single crystals

AbstractThe Hall effect and the conductivity in a low electric field and the conductivity in a pulsed high electric de‐field were investigated on carefully prepared and long‐time annealed samples. The reproducible experimental findings obtained at largely undistorted crystals were compared with calculated values. The calculations were carried out for a simple isotropic but non‐parabolic energy band model and for different scattering mechanisms. The result, which states that the temperature dependence of the mobility within the range extending from 65 to 180 K as well as the field dependence of drift velocity up to approximately 1.5 kV/cm, can be explained only by means of polar optical scattering for a parabolic energy band structure, can serve as a starting point for more detailed analyses.

Wave Instabilities in Bulk Semiconductors with Field-Dependent Drift Velocity and Carrier Temperature

Wave instabilities are studied considering the field dependencies of the drift velocity and the carrier temperature. Wave instabilities caused by negative dependency of the carrier temperature on an external field are derived. These instabilities are associated with the energy (transport) equation. The diffusion instability is derived for an extrinsic semiconductor, and it is shown that a negative value of the effective diffusion coefficient does not always lead to wave instability. The analysis in this paper is equally valid for a collision-dominated, weakly ionized gas plasma although it is presented with reference to semiconductors.

Field dependence of drift velocity of the &amp;#9001;100&amp;#9002; electrons in GaAs

Field dependence of drift velocity of the &amp;#9001;100&amp;#9002; electrons in GaAs