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Electron wave tunneling through a rectangular heterostructural emitter barrier is considered in the case of a homogeneous high-frequency (hf) alternating electric field directed normal to the barrier interfaces. This hf field leads not only to the well-known increase in a stationary tunnel current through the emitter barrier, which is proportional to EB2 (where EB is the electric-field amplitude) but also to a linear (∼EB) increase in an alternating current (ac) through this barrier with the same frequency ω as the electric-field frequency. The ac is a sharp function of ω, which grows significantly with an increase in ω (typically in the terahertz range). In a certain intermediate current and frequency region, the above-mentioned increase in the ac is the dominating effect of the alternating field. Such an effect can be used to optimize tunnel barrier emitters for ballistic transit-time terahertz-range oscillators. [ABSTRACT FROM AUTHOR]

We develop an analytic theory based on an earlier model of the admittance of a ballistic transit time diode terahertz oscillator with tunnel emission of electrons into a transit space. The focus of this work is on the actual case when electrons are injected with high enough energy to move from the start with maximal (saturated) ballistic velocity (∼1×10[sup 8] to 2×10[sup 8] cm/s). On the one hand, such diodes have maximal oscillation frequencies and, on the other hand, a simple analytic theory describes them and allows us to avoid a cumbersome numerical procedure, which characterizes the general case. Such a description is analogous to the description of oscillatory diodes with diffusive transport and saturated drift velocity. We have also considered a special case when a small part of the ballistic electrons crossing the transit space scatter into a diffusive subsystem with a small drift velocity. The appearance of such slow-drifting electrons substantially increases space charge in the transit space and influences the static JV-characteristic but the high-frequency admittance is almost invariable. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have considered interactions between ballistic (or quasiballistic) electrons accelerated by a dc electric field in an undoped transit space (T space) and a small ultrahigh frequency ac electric field and have calculated the linear admittance of the T space. Electrons in the T space have a conventional, nonparabolic dispersion relation. After consideration of the simplest specific case when the current is limited by the space charge of the emitted electrons, we turned to an actual case when the current is limited by a heterostructural tunnel barrier (B barrier) separating the heavily doped cathode contact and the T space. We assumed that the B barrier is much thinner than the T space and both dc and ac voltages drop mainly across the T space. The emission tunnel current through the B barrier is determined by the electric field E(0) in the T space at the boundary B barrier/T space. The more substantial is, the tunnel current limitation the higher the electric field E(0) becomes. We have shown that for a space-charge limited current the change from parabolic dispersion to the nonparabolic branch induces narrowing and closing of the frequency windows of transit-time negative conductance starting with the lowest-frequency windows. These narrowing and closing frequency windows become effective only for very high voltages U across the T space: U>mV[sub S][sup 2]/2e, where m is the effective mass for the parabolic branch and V[sub S] is the saturated velocity for the nonparabolic branch. For moderate voltages U, the effects of nonparabolicity are not very substantial. The tunnel current limitation decreases the space-charge effects in the T space and diminishes the role of the detailed electron dispersion relation. As a result, restoration of the frequency windows of transit-time negative conductance and an increase in the value of this negative conductance occur. The implementation of the considered tunnel injection transit time oscillator diode promises to lead to... [ABSTRACT FROM AUTHOR]

Discusses a study on the Wigner function simulations of structures of resonant tunneling diodes with high peak-to-valley ratios. Methods and equations; Device structure and direct current simulation results; Small-signal analysis and estimated power generation.

Discusses a study which presented a boundary condition method to simulate the interaction with ideal particle reservoirs at the device boundaries. Factor that impeded the numerical solution of the time-dependent Schrödinger equation for resonant-tunneling diodes; Way in which the transient and small-signal behavior of resonant-tunneling diodes were calculated; Requirement of the open nature of the semiconductor device problem.

A figure-of-merit expression is derived for resonant tunneling diodes being used as millimeter-wave sources. It is found that for very high-frequency applications the most important parameter is the ratio of the peak current to the device capacitance. Results for lattice-matched and pseudomorphic InP-based resonant tunneling structures that have a high figure-of-merit are presented. [ABSTRACT FROM AUTHOR]

A self-consistent quantum mechanical simulation is used to study the effect of spacer layer thickness on such resonant tunneling diode properties as the peak current and peak-to-valley current ratio. It is found that with a low cathode doping the peak current is insensitive to the commonly used spacer layer thickness. However, for higher cathode doping the peak current decreases with increasing spacer layer thickness. This phenomenon is explained on the basis of the junction potential between the heavily doped cathode contact region and the undoped double-barrier region. Thus, for device applications where a high current density is desired the cathode spacer layer should be designed as thin as possible. [ABSTRACT FROM AUTHOR]

The effect of incorporating a spatially variable effective mass in the Schrödinger equation method of resonant tunneling device modeling is investigated. It is shown that inclusion of this effect can produce an order of magnitude difference in the calculated peak current density of the static current voltage (I-V) curve for the resonant tunneling diode. Results for a particular In0.53Ga0.47As-AlAs structure show that much better agreement between theory and experiment is obtained by including this effect. Also, comparison of transient results for an In0.53Ga0.47As-In0.52Al0.48As structure shows a significant change in the diode switching transients. [ABSTRACT FROM AUTHOR]

Intrinsic bistability has been observed experimentally and attributed to the effect on the potential profile from stored charge in the quantum well through Poisson’s equation. This effect leads to two possible current states corresponding to a single voltage within the negative resistance region. In this letter a simulation method is presented which clearly shows bistability in the current-voltage curve of a resonant tunneling diode. This method self-consistently combines a Thomas–Fermi equilibrium model for the electron concentrations outside the double-barrier structure with a quantum calculation for the concentration inside the structure. [ABSTRACT FROM AUTHOR]