275 research outputs found
Current self-oscillations, spikes and crossover between charge monopole and dipole waves in semiconductor superlattices
Self-sustained current oscillations in weakly-coupled superlattices are
studied by means of a self-consistent microscopic model of sequential tunneling
including boundary conditions naturally. Well-to-well hopping and recycling of
charge monopole domain walls produce current spikes (high frequency modulation)
superimposed on the oscillation. For highly doped injecting contacts, the
self-oscillations are due to dynamics of monopoles. As the contact doping
decreases, a lower-frequency oscillatory mode due to recycling and motion of
charge dipoles is predicted. For low contact doping, this mode dominates and
monopole oscillations disappear. At intermediate doping, both oscillation modes
coexist as stable solutions and hysteresis between them is possible.Comment: 4 pages, 4 figure
Fin-array tunneling trigger with tunable hysteresis on (001) silicon substrate
We report the fabrication and characterization of a GaAs fin-array tunneling trigger monolithically integrated on an exact (001) silicon substrate. A Schmitt-trigger-like behavior was observed under double sweep condition by connecting the tunnel diode with an on-chip load resistor. The tunneling trigger circuit was studied using load line analysis. Critical parameters of the circuit were extracted. We found that the circuit hysteresis can be tuned by tailoring of the diode dimensions and load resistor value
Epitaxial designs for maximizing efficiency in resonant tunnelling diode based terahertz emitters
We discuss the modelling of high current density InGaAs/AlAs/InP resonant tunneling diodes to maximize their efficiency as THz emitters. A figure of merit which contributes to the wall plug efficiency, the intrinsic resonator efficiency, is used for the development of epitaxial designs. With the contribution of key parameters identified, we analyze the limitations of accumulated stress to assess the manufacturability of such designs. Optimal epitaxial designs are revealed, utilizing thin barriers, with a wide and shallow quantum well that satisfies the strained layer epitaxy constraint. We then assess the advantages to epitaxial perfection and electrical characteristics provided by devices with a narrow InAs sub-well inside a lattice-matched InGaAs alloy. These new structures will assist in the realization of the next-generation submillimeter emitters
Analytic Approach to the Operation of RTD Ternary Inverters Based on MML
Open Access.Multiple-valued Logic (MVL) circuits are one of the most attractive applications of the Monostable-to-Multistable transition Logic (MML), and they are on the basis of advanced circuits for communications. However, a proper design is not inherent to the usual MML circuit topologies. This paper analyses the case of an MML ternary inverter, and determines the relations that circuit representative parameters must verify to obtain a correct behaviour.This work has been funded by the Spanish Government under project NDR, TEC2007- 67245/MIC, and the Junta de AndalucÃa through the Proyecto de Excelencia TIC-2961.Peer Reviewe
Tristate memory cells using double-peaked fin-array III-V tunnel diodes monolithically grown on (001) silicon substrates
We demonstrate functional tristate memory cells using multipeaked GaAs/InGaAs fin-array tunnel diodes grown on exact (001) Si substrates. On-chip connection of single-peaked tunnel diode arrays produces I–V characteristics with multiple negative-differential resistance regions. We designed and fabricated two types of tristate memory cells. In one design, a double-peaked tunnel diode was used as the drive, and a reverse-biased single-peaked tunnel diode was used as the load. In the other design, the tristate memory cell was realized by the series connection of two forward-biased single-peaked tunnel diode
Simulation and Modeling of Novel Electronic Device Architectures with NESS (Nano-Electronic Simulation Software): A Modular Nano TCAD Simulation Framework
The modeling of nano-electronic devices is a cost-effective approach for optimizing the
semiconductor device performance and for guiding the fabrication technology. In this paper, we
present the capabilities of the new flexible multi-scale nano TCAD simulation software called NanoElectronic Simulation Software (NESS). NESS is designed to study the charge transport in contemporary and novel ultra-scaled semiconductor devices. In order to simulate the charge transport in
such ultra-scaled devices with complex architectures and design, we have developed numerous
simulation modules based on various simulation approaches. Currently, NESS contains a driftdiffusion, Kubo–Greenwood, and non-equilibrium Green’s function (NEGF) modules. All modules
are numerical solvers which are implemented in the C++ programming language, and all of them
are linked and solved self-consistently with the Poisson equation. Here, we have deployed some of
those modules to showcase the capabilities of NESS to simulate advanced nano-scale semiconductor
devices. The devices simulated in this paper are chosen to represent the current state-of-the-art and
future technologies where quantum mechanical effects play an important role. Our examples include
ultra-scaled nanowire transistors, tunnel transistors, resonant tunneling diodes, and negative capacitance transistors. Our results show that NESS is a robust, fast, and reliable simulation platform which
can accurately predict and describe the underlying physics in novel ultra-scaled electronic devices.European Union Horizon 2020 - 688101 SUPERAID7EPSRC UKRI Innovation Fellowship - EP/S001131/1 (QSEE), No.
EP/P009972/1 (QUANTDEVMOD)H2020-FETOPEN-2019 s-
No.862539-Electromed-FET OPEN.No. EP/S000259/1(Variability PDK for design based research on FPGA/neuro computing
Diode effect in Josephson junctions with a single magnetic atom
Current flow in electronic devices can be asymmetric with bias direction, a
phenomenon underlying the utility of diodes and known as non-reciprocal charge
transport. The promise of dissipationless electronics has recently stimulated
the quest for superconducting diodes, and non-reciprocal superconducting
devices have been realized in various non-centrosymmetric systems. Probing the
ultimate limits of miniaturization, we have created atomic-scale Pb--Pb
Josephson junctions in a scanning tunneling microscope. Pristine junctions
stabilized by a single Pb atom exhibit hysteretic behavior, confirming the high
quality of the junctions, but no asymmetry between the bias directions.
Non-reciprocal supercurrents emerge when inserting a single magnetic atom into
the junction, with the preferred direction depending on the atomic species.
Aided by theoretical modelling, we trace the non-reciprocity to quasiparticle
currents flowing via Yu-Shiba-Rusinov (YSR) states inside the superconducting
energy gap. Our results open new avenues for creating atomic-scale Josephson
diodes and tuning their properties through single-atom manipulation
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