Polariton Condensate Transistor Switch

A polariton condensate transistor switch is realized through optical excitation of a microcavity ridge with two beams. The ballistically ejected polaritons from a condensate formed at the source are gated using the 20 times weaker second beam to switch on and off the flux of polaritons. In the absence of the gate beam the small built-in detuning creates potential landscape in which ejected polaritons are channelled toward the end of the ridge where they condense. The low loss photon-like propagation combined with strong nonlinearities associated with their excitonic component makes polariton based transistors particularly attractive for the implementation of all-optical integrated circuits

Quantum reflections and the shunting of polariton condensate wave trains: implementation of a logic AND gate

We study the dynamics of polariton condensate wave trains that propagate along a quasi one-dimensional waveguide. Through the application of tuneable potential barriers the propagation can be reflected and multiple reflections used to confine and store a propagating state. Energy-relaxation processes allow the delayed relaxation into a long-living coherent ground state. Aside the potential routing of polariton condensate signals, the system forms an AND-type logic gate compatible with incoherent inputs.Comment: 9 pages, 5 figures, 2 table

High Power Self-Aligned, Trench-Implanted 4H-SiC JFETs

The process technology for the fabrication of 4H-SiC trenched-implanted-gate 4H–SiC vertical-channel JFET (TI-VJFET) has been developed. The optimized TIVJFETs have been fabricated with self-aligned nickel silicide source and gate contacts using a process sequence that greatly reduces process complexity as it includes only four lithography steps. A source-pillars sidewall oxidation and subsequent removal of the metallization from the top of the sidewall oxide ensured isolation between gate and source. Optimum planarization of the source pillars top has been performed by cyclotene spin coating and etch back. The effect of the channel geometry on the electrical characteristics has been studied by varying its length (0.3 and 1.2μm) and its width (1.5-5μm). The voltage blocking exhibits a triode shape, which is typical for a static-induction transistor (SIT) operation. The transistors exhibited high ON current handling capabilities (Direct Current density >1kA/cm2) and values of RON ranging from 6 - 12 mΩ•cm2 depending on the channel length. Maximum voltage blocking was 800V limited by the edge termination. The maximum voltage gain was 51. Most transistors were normally-on. Normally-off operation has been observed for transistors lower than 2μm channel width (mask level) and deep implantation

Electrical tuning of nonlinearities in exciton-polariton condensates

S. T. acknowledges the financial support of the Stavros Niarchos Foundation within the framework of the project ARCHERS, P. S. acknowledges support form the bilateral Greece-Russia Polisimulator project cofinanced by Greece and the EU Regional Development Fund, A. T. acknowledges the Russian-Greek support from the project supported by the Ministry of Education and Science of The Russian Federation (Project No. RFMEFI61617X0085).A primary limitation of the intensively researched polaritonic systems compared to their atomic counterparts for the study of strongly correlated phenomena and many-body physics is their relatively weak two-particle interactions compared to disorder. Here, we show how new opportunities to enhance such on-site interactions and nonlinearities arise by tuning the exciton-polariton dipole moment in electrically biased semiconductor microcavities incorporating wide quantum wells. The applied field results in a twofold enhancement of exciton-exciton interactions as well as more efficiently driving relaxation towards low energy polariton states, thus, reducing condensation threshold.PostprintPeer reviewe

Stress-corrosion mechanisms in silicate glasses

The present review is intended to revisit the advances and debates in the comprehension of the mechanisms of subcritical crack propagation in silicate glasses almost a century after its initial developments. Glass has inspired the initial insights of Griffith into the origin of brittleness and the ensuing development of modern fracture mechanics. Yet, through the decades the real nature of the fundamental mechanisms of crack propagation in glass has escaped a clear comprehension which could gather general agreement on subtle problems such as the role of plasticity, the role of the glass composition, the environmental condition at the crack tip and its relation to the complex mechanisms of corrosion and leaching. The different processes are analysed here with a special focus on their relevant space and time scales in order to question their domain of action and their contribution in both the kinetic laws and the energetic aspects.Comment: Invited review article - 34 pages Accepted for publication in J. Phys. D: Appl. Phy

A study of hopping transport during discharging in SiNx films for MEMS capacitive switches

A more realistic approach of the discharging process in MEMS capacitive switches is presented with the introduction of the effective temperature in order to determine the behavior of the microscopic parameters of hopping conduction, which dominates the process. The use of Kelvin Probe method in MIM capacitors that simulates the discharging process in MEMS switches during up-state revealed that both the increase of temperature and stressing field intensity results the decrease of mean hopping length. This result arises from the simultaneous contribution of the transport energy levels associated with the impact of the stressing field and temperature. Also, a correlation was found experimentally between the stretched exponential decay and the hopping process. The proposed method was also applied in MEMS switches where a similar behavior of the hopping parameters was found, providing evidence that the control of the hopping length to an optimum value can provide fast discharging and low leakage currents, increasing the device lifetime. © 2020 Elsevier Lt

Electrical properties of SiNx films with embedded CNTs for MEMS capacitive switches

The present paper aims to provide a better insight on the electrical properties of silicon nitride (SiNx) dielectric films with embedded carbon nanotubes (CNTs) that can be used in RF MEMS capacitive switches. The effect of the embedded CNTs on the leakage current density and on the discharging processes of the films has been probed with the aid of metal-insulator-metal (MIM) capacitors and it has been found that the presence of CNTs results in an increase of leakage current density as well as to an acceleration of the charge displacement through the bulk of the dielectric films. Finally, the charging and discharging processes have been investigated in MEMS capacitive switches and it has been found that the use of CNTs in SiNx films results in an enhancement of charging processes but it also accelerates the discharging process. © 2017 Elsevier Lt

Thermally activated discharging mechanisms in SiNx films with embedded CNTs for RF MEMS capacitive switches

In the present work, we investigate thermally activated processes in nanostructured SiNx films with embedded CNTs, which can be used in RF MEMS capacitive switches. Nanostructured films have been fabricated with a simple process, in order to incorporate CNTs on the lower SiNx layer and a reference SiNx material has been also fabricated with the same method (without CNTs), in order to compare the properties of the nanostructured films with the pristine material. Thermally stimulated depolarization currents (TSDC) assessment and a single-point Kelvin Probe (KP) system have been used in MIM capacitors, in order to investigate the electrical properties of the utilized films. The nanostructured material is found to exhibit lower charging and smaller discharging time, which makes it a promising candidate for RF MEMS capacitive switches. Thermally activated discharging mechanisms have been identified and the presence of CNTs is found to diminish a discharging mechanism with a characteristic time larger than five days at room temperature. Different discharging mechanisms are identified and distinguished for the first time, to the best of our knowledge, between a reference and a nanostructured SiNx dielectric film. Charge displacement in the bulk material during discharge takes place through hopping processes and larger mean hopping distance and zero field conductivity has been found in the nanostructured films. The reduction of the discharge characteristic time and the simultaneous suppression of trapping centers in the films with embedded CNTs indicate a direct relation between the macroscopic electrical properties and the microscopic defects in the dielectric material. © 2020 Elsevier B.V