Saturation Of Electron Drift Velocity Research Articles

The influence of saturation of electron drift velocity on photorefractive effect in GaAs/AlGaAs quantum wells structures

The structures of the semi-insulating quantum wells based on GaAs/AlGaAs material composition are photorefractive materials of high sensitivity and short time of response. An important factor affecting the course of the photorefractive phenomenon in these materials is the nonlinear relationship between the velocity of electrons and the intensity of the electric field. The article compares two most frequently used models of nonlinear transport of electrons in GaAs: a classic two-valley model and an empirical model accounting for the saturation of the dependence of electron velocity on electric field intensity. It has been shown how the selection of the model influences the predicted distribution of space-charge field during the photorefractive two-wave mixing, which allows evaluating the correctness of the use of these models.

Parameters of pulse generators based on 4H : SiC sharp-recovery drift diodes: The influence of electron drift velocity saturation

The generation of high-voltage electrical pulses by generators based on 4H : SiC sharp-recovery drift diode is demonstrated. It is shown that the electron drift velocity saturation influences the shape of output pulses.

Effects of Self-Heating on Performance Degradation in AlGaN/GaN-Based Devices

A self-consistent electrothermal transport model that couples electrical and thermal transport equations is established and applied to AlGaN/GaN device structures grown on the following three different substrate materials: 1) SiC; 2) Si; and 3) sapphire. Both the resultant I-V characteristics and surface temperatures are compared to experimental I -V measurements and Raman spectroscopy temperature measurements. The very consistent agreement between measurements and simulations confirms the validity of the model and its numerical rendition. The results explain why the current saturation in measured I-V characteristics occurs at a much lower electric field than that for the saturation of electron drift velocity. The marked difference in saturated current levels for AlGaN/GaN structures on SiC, Si, and sapphire substrates is directly related to the different self-heating levels that resulted from the different biasing conditions and the distinctive substrate materials.

Monte Carlo evaluation of an analytical model for nonequilibrium-phonon-induced electron velocity saturation in GaN

The ensemble Monte Carlo method is used to solve the Boltzmann equation for electrons together with the equation for phonons treated in the relaxation-time approximation. The effect of nonequilibrium longitudinal optical phonons on hot-electron energy distribution, mean energy, drift velocity and power dissipation is considered for bulk GaN subjected to electric fields in a range up to 100 kV cm−1. In particular, the suppression of the high-energy tail of the hot-electron distribution due to the phonon accumulation is resolved. The results of the simulation are compared with those obtained within the recently proposed analytical model for the saturation of electron drift velocity at high electric fields. The saturated velocity decreases as the electron gas density increases. Values around 107 cm s−1 are reached at an electric field of 100 kV cm−1 for an electron gas density of 1018 cm−3. The analytically obtained results are in a better agreement with those of Monte Carlo simulation if the electron gas density is higher and the electric field is stronger.

Sub-quarter-micrometer n-channel MOSFET's fabricated with direct ion-beam Nitridation

N-channel MOSFET's with physical gate lengths as short as 0.19 µm were fabricated with direct e-beam writing and high resolution pattern transfer techniques. The gate oxide thickness was 8.3 nm with a channel doping level of 1 × 1018cm-3. An ion beam nitridized film was used as a selective oxidation mask during the growth of the field oxide. The resulting lateral encroachment of the field oxide was 0.25 µm per device edge which was much less than that of the conventional LOCOS process. The transport mechanism in the 0.19 µm gate length transistor was limited by the electron drift velocity saturation. The rough surface created by the ion beam nitridation step limited the value of the saturation velocity. Intrinsic transconductance of 140 mS/ram was measured. The oxide fields needed to produce 10-6A/cm2leakage current through the gate oxide was about 7 MV/cm for the positively biased gate and 8.8 MV/cm for the negatively biased gate.

A Possible Explanation of the Observed Electron Drift Velocity Saturation in Solid Ar, Kr, and Xe

The recently published drift velocity measurements of excess electrons in solid Ar, Kr, and Xe show a complete saturation of the drift velocity with applied field between ${10}^{4}$ and ${10}^{5}$ V ${\mathrm{cm}}^{\ensuremath{-}1}$. In this paper it is suggested that the interaction of the conduction electrons with the periodic structure is the basic velocity-limiting mechanism in these solids. The model is supported by a simple calculation in which an energy-dependent effective mass is included in the Shockley hot electron theory. The computed field dependence of the drift velocity, involving one adjustable parameter, is in good agreement with the observed curves for solid Ar, Kr, and Xe over the complete range of applied fields.

High-speed current limiters

Current limiters based on the high-field saturation of electron-drift velocity in germanium have been fabricated by making two closely spaced ohmic contacts to a surface n-layer diffused into Ge. In operation, current flows from contact to contact through the n-layer. Current saturation begins at a voltage V_{s} = E_{s} d , where d is the contact spacing and E s is the field for saturation of electron drift velocity. Generally, in order to work at reasonable signal levels (volts and milliamperes) a structure small in all dimensions is required. A diffused-layer structure provides a convenient way of meeting this requirement and, at the same time, has, first, a high surface-to-volume ratio which facilitates heat removal and, second, a p-n junction which minimizes conductivity modulation by removing avalanche-generated holes. Limiters with d \cong 2 µ, and 10 µ × 10 µ contacts, were fabricated on Sb-diffused layers of 103-Ω sheet resistance and ∼1017cm-3surface concentration. Limiting current was ∼2.5 mA and limiting extended from ∼2 to 16 V. The conductance in the limiting range was ∼40 µmho and a contact-to-contact capacitance was ∼0.1 pF.