Metal-glass contacts in high electric fields

In the presence of high electric fields, the region adjacent to a metallic anode of an ionic conducting glass quickly becomes depleted of mobile ionic carriers. At the cathode, however, electrons are injected into the glass from the metal electrode and cause the effective conductivity of this region to increase.     

Negative electron diffusivity in high electric fields

The prediction that the electron diffusivity may be negative in high electric fields under some conditions has been examined starting from the Boltzmann equation and assuming a Maxwellian distribution function. It is found that the diffusion constant is positive for predominant acoustic phonon, polar optical phonon or impurity atom scattering. But the constant may be negative when effects of nonparabolicity are important and energy relaxation is limited by non-polar optical phonon scattering but the momentum relaxation is dominated by impurity atom scattering. Calculations with the parameter values of InSb, silicon and germanium show that only in materials like germanium at low temperatures of about 27 K the diffusion constant may be negative for impurity concentrations of 10¹⁷–10¹⁸ cm^?3.     

Transient space-charge phenomena in semiconductors at high electric fields

The transient response of trap-free semiconductors subjected to a voltage step function and unipolar injection of charge is analyzed for the case that the velocity of the carriers is a non-linear function of the electric field. The method of characteristics is used to evaluate current, density and field profiles as functions of time. Numerical results are presented for the case of n-Si. These results show that there is a sharp bunching of charge accompanying the cusp. This bunching of charge is shown to be a consequence of the decreased differential mobility at high fields.These results are compared with the previously published results for a constant mobility case. A simple model is used to derive exactly the results for a saturated-velocity transient. It is shown that the numerical results for the actual case of non-linear velocity fit well between the results for these two limiting behaviors for the velocity-field curve.Effects of a finite rise-time in the voltage pulse are also studied. It is shown that a significant rise time can considerably reduce the sharpness of the current cusp.     

Electrical characterization and reliability study of HEMTs on composite substrates under high electric fields

The electrical characterization, in DC and pulsed regime, and reliability analysis of T-gate high electron mobility transistors built on SiCopSiC and SopSiC composite substrates under high electric fields are here presented. The impact of different gate–drain overhang lengths on the electrical behavior of SiCopSiC devices is also investigated. We will demonstrate that devices can be efficiently realized over the proposed composite substrates, and that performances and robustness are comparable to devices processed on SiC or sapphire. The sensitivity to ESD-like events is also reported, using emission microscope for the failure analysis investigation.     

Electron velocity in n GaAs at high electric fields

The velocity of electrons in n GaAs has been measured for electric fields in the range 20?55 kV/cm by the time-of-flight technique. The velocity was found to decrease slowly wlth increasing electric field, and is 8.09×106 cm/s at 55 kV/cm.     

Electron transport properties in GaAs at high electric fields

Electron distribution function, drift velocity, mean energy, valley population fractions and diffusion coefficient were calculated at high, up to 100 kV/cm, electric fields. Calculations were carried out by the Monte Carlo method. The three-valley model of GaAs conduction band was used. The obtained results were compared with the experimental data.     

Far-infrared radiation from n-InGaAs/GaAs quantum-well heterostructures in high lateral electric fields under injection conditions

The infrared radiation emitted by hot electrons in n-InGaAs/GaAs quantum-well heterostructures subjected to a lateral electric field is investigated under conditions of carrier injection from the current contacts. In structures with double tunneling-coupled wells one of which is δ-doped, a pronounced increase in the intensity of far-infrared radiation upon the onset of carrier injection is observed. At the same time, this effect is lacking in single-quantum-well structures with doped wells or barriers. The observed increase in the radiation intensity is associated with the direct intersubband transitions of electrons which contribute to emission upon the real-space transfer of charge carriers between wells. The intensity of these transitions increases due to compensation of the space charge existing between the wells by the injected holes.     

Electronic properties of BN nanocones under electric fields

The electronic properties of BN nanocones with 240° disclination under electric fields are investigated using first-principles calculations based on the density-functional theory. The cones are studied under the influence of electric fields, up to 1.13 V/Å, applied along the cone axis. The densities of states (DOS) of these BN nanocones show different patterns depending on the termination two atoms (BN, BB or NN) and the electric field strength. A decreasing of the gap is observed with increasing field. The field emission properties are very sensitive to the DOS and we show that the termination atoms, as well as the electric field, contribute to enhance the electron field emission.     

Drift velocity of electrons in quantum wells in high electric fields

It is experimentally found that the maximum drift velocity of electrons in quantum wells of differently arranged AlGaAs/GaAs heterostructures and pseudoamorphous Al_0.36Ga_0.64As/In_0.15Ga_0.85 As heterostructures is higher than the maximum drift velocity of electrons in bulk materials. It is established that no negative differential conductivity is exhibited by the field dependence of the drift velocity of two-dimensional electrons in GaAs and In_0.15Ga_0.85As. The drift velocity in the GaAs quantum well is saturated in fields several times higher than the field corresponding to the Γ-L intervalley transitions of electrons in bulk GaAs.     

Electron drift velocity in n-GaAs at high electric fields

Measurements have been made on the drift velocity of electrons in n-GaAs by the time-of-flight technique. The method of determining the $\text{ν}\text{E}$ characteristics from the transit time across the non-uniform field depletion region of the sample is described. Velocity/field curves are presented in the field range 20 to 113 kV/cm at various temperatures from 130 to 400°K. All curves show the velocity to decrease slowly as the field is increased and velocity saturation is approached at the highest field values used. The characteristics match up well with the generally accepted experimental curves at the lower fields, and a simple theory is described which predicts well the saturation velocity.     

Transport of electrons in a GaAs quantum well in high electric fields

The rates of intrasubband and intersubband scattering of electrons by polar optical and intervalley phonons are determined in relation to the electron energy and width of a deep rectangular quantum well in GaAs. The Monte Carlo method was used to calculate the field dependences of the electron’s drift velocity in quantum wells with the width of 10, 20, and 30 nm. It is shown that the drift velocity in high electric fields in a quantum well vastly exceeds the maximum drift’s saturation velocity in the bulk material.     

Electrical conductivity of amorphous films of chalcogenide compounds in high electric fields

Effect of the electric field’s strength and temperature on the electrical conductivity of amorphous thin films of chalcogenide compounds has been studied. It is demonstrated that, at strengths of the electric field exceeding 10⁴ V cm^?1, the current increases exponentially as the voltage is increased. The activation energy of the temperature dependence of the conductivity decreases as the strength of the electric field is increased. A model that satisfactorily describes the experimental data is suggested on the basis of the assumption that the increase in the carrier concentration with the field strength has a dominant effect on the conductivity. The effective carrier’s mobility of ～10^?2 cm² V^?1 s^?1 and the activation length of ～(10–30) nm, which represents the influence of the electric field, are used as characteristic parameters of the model.     

Electron and hole ionization rates in epitaxial silicon at high electric fields

Ionization rates for electrons and holes are extracted from photomultiplication measurements on silicon p⁺n mesa diodes for electric fields of 2·0 × 10⁵?7·7 × 10⁵ V/cm at temperatures of 22, 50, 100 and 150°C. These results are particularly pertinent to the analysis of high-frequency (～ 100 GHz) silicon IMPATT diodes.The rates obtained here are in reasonable agreement with previously published data of van Overstraeten and DeMan, although slightly larger in magnitude. Calculated curves of breakdown voltage vs background doping level are presented using the room temperature ionization rates. Also a comparison is made to previously reported rates. The new rates provide a closer agreement between predicted and measured breakdown voltages for breakdown voltages less than 70 V.     

Noise in silicon and FET's at high electric fields

The noise temperature of n-type silicon was measured on an epitaxial layer up to a field strength of 10 KV/cm from 1 to 20 MHz at 77°K. The result was applied to obtain an approximate form for the drain noise of an FET in the high electric field. We found that the noise increases in proportion to the product of the drain current and voltage in high electric fields. The noise of the FET was also measured and the experimental data show reasonable agreement with the theoretical expressions.     

Effects of high electric fields and temperature on conductivity of a-Si

At high electric fields the Poole-Frenkel effect and thermally-assisted tunneling give rise to an enhanced electric conductivity of amorphous silicon (a-Si). The occupancy of states in the gap, free, and trapped charge carrier concentrations and electric conductivity of a homogenous a-Si in steady-state conditions are calculated on the basis of space-charge neutrality and with time-unchangeable concentrations of charge carriers. Simplifying approximations are introduced, thus enabling easier calculations of carrier concentrations and conductivity. The theory of capture-emission dynamics in a-Si at high fields is further extended by expressing occupancy functions and nonequilibrium quasi-Fermi levels. Effects of the density of states distribution in a-Si and added impurities upon carrier concentrations and conductivity are revealed.     

Current-voltage characteristics of electric contacts on p-type ZnSe

The current-voltage characteristics of electric contacts made of different materials on p-type ZnSe that form Schottky barriers from 0.3 to 1.2 eV are studied theoretically using the formula $$J = \frac{{A^* T}}{k}\int_0^\infty {T(E)[F(E) - F(E - eV)]dE,} $$ where T(E) is the energy-dependent quantum tunneling probability and F(E) is the Fermi distribution function. The contribution to the total current of both the thermionic emission and the tunneling are therefore included. The net doping concentrations under study range from 1.0×10¹⁷ cm^?3 to 1.0×10¹⁹ cm^?3. The reverse bias voltage across the barrier at a current density of 200 A/cm² is used to assess whether the barrier is reduced to an ohmic contact. A barrier of 0.3 eV is already an ohmic contact at doping concentration p=1.0×10¹⁷ cm^?3, while a barrier of 1.2 eV still behaves like a diode event at p=1.0×10¹⁹ cm^?3.     

Tunneling emission of electrons from semiconductors’ valence bands in high electric fields

Tunneling emission currents of electrons from semiconductors to vacuum (needle-shaped GaAs photodetectors) and to a metal (silicon metal-insulator-semiconductor diodes with a tunneling-transparent insulator layer) are studied in high and ultrahigh electric fields. It is shown that, in semiconductors with the n-type conductivity, the major contribution to the emission current is made by the tunneling emission of electrons from the valence band of the semiconductor, rather than from the conduction band.     

Impact of high tunneling electric fields on erasing instabilities in NOR flash memories

Experimental data and analysis show that overerase effects in NOR Flash memories increase with the electric field used during erasing. We found that the electric field is an accelerating factor for cell degradation during cycling. Tunnel oxide degradation reaches a critical level above which the cell starts showing erased threshold voltage instabilities possibly leading to single bit failure. Experimental data show that cell degradation during erasing has to be ascribed to hole injection rather than to electron injection and that both hole trapping and detrapping increase with the electric field. The total stress time required to reach the critical degradation level has been found to follow a 1/E/sub ox/ exponential dependence which is similar to the oxide breakdown phenomena thus establishing a physical link between the two phenomena. Anode Hole Injection has been suggested as hole generation and injection mechanism occurring during erasing and it is shown to be consistent with the experimental data.     

Extension of impact-ionization multiplication coefficientmeasurements to high electric fields in advanced Si BJT's

Measurements of the impact-ionization multiplication coefficient M-1 in advanced Si BJTs up to values in excess of 10 (corresponding to a peak electric field at the base-collector junction of about 9×10⁵ V/cm) are presented. The intrinsic limitations affecting M-1 measurements at high electric fields are discussed. In particular, the fundamental role played by the negative base current and the parasitic base resistance in determining instabilities during M-1 measurements is pointed out. An accurate theoretical prediction of the M-1 coefficient on collector-base voltages close to BV_CBO requires that the contribution of holes to impact ionization be properly accounted for