On stochastic switching of bistable resonant-tunneling structures via nucleation

We estimate the critical size of the initial nucleus of the low current state in a bistable resonant tunneling structure which is needed for this nucleus to develop into a lateral switching front. Using the results obtained for deterministic switching fronts, we argue that for realistic structural parameters the critical nucleus has macroscopic dimensions and therefore is too large to be created by stochastic electron noise.Comment: the extended version of the Comment on "Lifetime of metastable states in resonant-tunneling structures" to appear in Phys. Rev.

Experimental Study of Pressure Influence on Tunnel Transport into 2DEG

We present the concept and the results of pilot measurements of tunneling in a system {Al/$\delta_{Si}$-GaAs} under pressure up to 2 GPa at 4.2 K. The obtained results may indicate the following: the barrier height for {Al/$\delta$-GaAs} equals to 0.86 eV at P=0 and its pressure coefficient is $3 meV/kbar$; charged impurity density in the delta-layer starts to drop from $4.5\times 10^{12} cm^{-2}$ down to $3.8\times 10^{12} cm^{-2}$ at about 1.5 GPa; metal-insulator transition may occur in 2DEG at about 2 GPa

Lateral current density fronts in asymmetric double-barrier resonant-tunneling structures

We present a theoretical analysis and numerical simulations of lateral current density fronts in bistable resonant-tunneling diodes with Z-shaped current-voltage characteristics. The bistability is due to the charge accumulation in the quantum well of the double-barrier structure. We focus on asymmetric structures in the regime of sequential incoherent tunneling and study the dependence of the bistability range, the front velocity and the front width on the structure parameters. We propose a sectional design of a structure that is suitable for experimental observation of front propagation and discuss potential problems of such measurements in view of our theoretical findings. We point out the possibility to use sectional resonant-tunneling structures as controllable three-terminal switches.Comment: to appear in J.Appl.Phy

Time--delay autosynchronization of the spatio-temporal dynamics in resonant tunneling diodes

The double barrier resonant tunneling diode exhibits complex spatio-temporal patterns including low-dimensional chaos when operated in an active external circuit. We demonstrate how autosynchronization by time--delayed feedback control can be used to select and stabilize specific current density patterns in a noninvasive way. We compare the efficiency of different control schemes involving feedback in either local spatial or global degrees of freedom. The numerically obtained Floquet exponents are explained by analytical results from linear stability analysis.Comment: 10 pages, 16 figure

Operation of resonant-tunnelling oscillators beyond tunnel lifetime limit

The tunnel lifetime of the electrons in the quantum well of a resonant-tunnelling diode (RTD) is usually assumed to be imposing an inherent fundamental limitation on the operating frequencies of RTD oscillators. Here, we experimentally demonstrate that one can overcome the limitation by heavy doping of the RTD collector. We present RTD oscillators with the fundamental oscillation frequency up to a factor of 3 above the tunnel lifetime limitation. Our results indicate that the inherent frequency limitations of RTDs should lie far above the state-of-the-art frequency of the contemporary RTD oscillators

Spectral characterization of broadband THz antennas by photoconductive mixing: toward optimal antenna design

The spectral characterization of a broadband antenna using a pump-probe photomixing continuous-wave (CW) terahertz (THz) system is presented. The high dynamic range of the system, comparable to or better than that of similar pump-probe systems reported in the literature, provides an accurate means of antenna characterization. The planar antenna exhibits a log-periodic behavior at low frequencies, a bow-tie behavior at high frequencies, and a resonance characteristic in between, well in agreement with the antenna geometry. It is predicted that an improved geometry that extends the log-periodic behavior to higher frequencies would contribute significantly in enhancing the broadband performance of antenna-coupled photomixers

Operation of resonant-tunnelling-diode oscillators beyond tunnel-lifetime limit at 564 GHz

We present resonant-tunnelling-diode (RTD) oscillators, which are operating at frequencies up to 564 GHz. Due to heavy doping of the collector side of our diodes, the oscillators are operating beyond the tunnel-lifetime (τ) and relaxation-time (τrel) limits of RTDs. At 564 GHz we achieve ωτ≈1.2 and ωτrel≈2.6, the highest previously reported value of ωτ at frequencies >150 GHz was ≈0.6. Our study indicates that operating frequencies of RTD oscillators could be significantly increased and RTDs should be capable of operating at frequencies of several THz

THz Electronics

Several key topics in THz electronics are discussed. We describe the operating principles, limitations, and state-of-the-art of resonant-tunnelling diodes (RTDs) and THz RTD oscillators. Furthermore, THz fundamental or sub-harmonic flip-chip Schottky diode mixer configurations are described. Different measurement techniques are commented and their properties are outlined. The chapter also relates the use of advanced mixer configurations. Fabrication technologies for Schottky-diode based structures for THz wave applications are included together with the low-barrier Schottky diode characterization for millimeter-wave detector design. Finally, LNAs for sub-millimeter waves are discussed, including up-to-date design approaches and resulting performance, with emphasis on the necessary technological modification to extend MMIC approaches toward the THz region