Tunneling Transit Time Research Articles

Self-consistent surface charges and electric field in p-i-n tunneling transit-time diodes based on single- and multiple-layer graphene structures

We develop a device model for p-i-n tunneling transit-time diodes based on graphene single- and multiple-layer structures operating at the reverse bias voltages. The model of the graphene tunneling transit-time diode (GTUNNETT) accounts for the features of the interband tunneling generation of electrons and holes and their ballistic transport in the device i-section, as well as the effect of the self-consistent electric field associated with the self-consistent charges of propagating electrons and holes. Using the developed model, we calculate the dc current-voltage characteristics and the ac frequency-dependent admittance as functions of the GTUNNETT structural parameters, in particular, the number of graphene layers.

Effect of self-consistent electric field on characteristics of graphene p-i-n tunneling transit-time diodes

We develop a device model for p-i-n tunneling transit-time diodes based on single- and multiple graphene layer structures operating at the reverse bias voltages. The model of the graphene tunneling transit-time diode (GTUNNETT) accounts for the features of the interband tunneling generation of electrons and holes and their ballistic transport in the device i-section, as well as the effect of the self-consistent electric field associated with the charges of propagating electrons and holes. Using the developed model, we calculate the dc current-voltage characteristics and the small-signal ac frequency-dependent admittance as functions of the GTUNNETT structural parameters, in particular, the number of graphene layers and the dielectric constant of the surrounding media. It is shown that the admittance real part can be negative in a certain frequency range. As revealed, if the i-section somewhat shorter than one micrometer, this range corresponds to the terahertz frequencies. Due to the effect of the self-consistent electric field, the behavior of the GTUNNETT admittance in the range of its negativity of its real part is rather sensitive to the relation between the number of graphene layers and dielectric constant. The obtained results demonstrate that GTUNNETTs with optimized structure can be used in efficient terahertz oscillators.

Negative terahertz dynamic conductivity in electrically induced lateral p–i–n junction in graphene

We analyze a graphene tunneling transit-time device based on a heterostructure with a lateral p–i–n junction electrically induced in the graphene layer and calculate its ac characteristics. Using the developed device model, it is shown that the ballistic transit of electrons and holes generated due to interband tunneling in the i-section results in the negative ac conductance in the terahertz frequency range. The device can serve as an active element of terahertz oscillators

Diamond Schottky Contact Transit-time Diode for Terahertz Power Generation

A diamond mixed tunneling and avalanche transit-time diode is designed in this letter. Schottky contact is used in this kind of diode to reduce the contact resistance. Electrical characteristics of n-type diamond Schottky contact have been accurately investigated. Total output power of such transit-time diode is evaluated using an accurate large-signal model. The results indicate that the new type transit-time diode can operate with the frequency up to several terahertzes. The output power density is more than 1.185 MW/cm2 from 1.07 to 2.12THz. About 17% improvement in efficiency is found at 2.12THz.

Rapid tunneling transit times for electrons and photons through periodic fragments

The complex band-structure method is used to examine tunneling transit times and velocities through periodic fragments. The analysis applies equally well to both electron tunneling through chainlike molecules and evanescent light passing through periodic dielectric photonic crystals. Analytic properties of the complex band structure produce branch points where the speed of (nonrelativistic Schrodinger) electron tunneling is unbounded, and evanescent light travels faster than c. The analysis is general, can be applied to very complex periodic systems, and produces a simple result for the tunneling transit time τ for both electrons and photons. In the limit of a very thick periodic tunneling region of thickness L, the transit time for electrons is τ =L/ν* g , where v* g is the generalized complex band-structure transmission group velocity, 1/v* g = ∞‖∂β/∂E‖, where β is the imaginary part of the complex wave vector. The derivative ∂β/∂E vanishes at the branch point of the complex band structure producing unbounded (or ultrafast) speeds. Analogous results are also found for photons.

Stable and efficient numerical method for solving the Schr�dinger equation to determine the response of tunneling electrons to a laser pulse

The form Ψ(x, t)=[F0(x)+F1(x, t)e−iωt+F−1(x, t)eiωt]e−iEt/ℏ is used for the wave function in the transient solutions. This expression is similar to the three dominant terms in the steady-state solution from the Floquet theory, except that now F1 and F−1 depend on t as well as x. The function F0 is the static solution, and separate partial differential equations are given for F1 and F−1. Polynomial extrapolation is used to satisfy boundary conditions at the ends of the grid. The numerical solutions are shown to converge and to be numerically stable even for simulated times exceeding 2000 cycles of the radiation field. The examples show delays corresponding to the semiclassical tunneling transit time, the classical time for traversing the inverted barrier. A resonance is seen when electrons promoted above the barrier by absorbing quanta from the radiation field have the closed line integral of momentum between the turning points equal to an integral multiple of Planck's constant. A second resonance occurs when the period of oscillation for the radiation equals the semiclassical tunneling transit time for electrons that absorb one photon from the radiation but are still below the barrier. This resonance decays at a rate corresponding to the tunneling dwell time, and, thus, it is not present in the steady state. These observations suggest a semiclassical picture of the tunneling process. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 703–710, 1998

Experimental analysis of resonant tunneling transit time using high-frequency characteristics of resonant tunneling transistors

We systematically estimate the resonant tunneling transit time from the high-frequency characteristics of resonant tunneling transistors. It is found that the transit time across an InGaAs/InAlAs resonant tunneling structure is more than one order of magnitude shorter than that for GaAs/AlAs with the same barrier layer thickness. In addition, the obtained times agree reasonably well with calculated phase time. It is probably the elastic resonance width and not the inelastic scattering effect that mainly determines the resonant tunneling transit time.