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Vorträge und Posterpräsentationen (ohne Tagungsband-Eintrag):

M. Feiginov:
"Physics of THz resonant-tunneling diodes";
Vortrag: THz Electronics Workshop, Glasgow, Scotland (eingeladen); 23.04.2018 - 24.04.2018.



Kurzfassung englisch:
Resonant-tunneling diodes (RTDs) have reemerged in the last years as a promising and viable technology for sub-THz and THz radiation sources. RTD oscillators working above 1 THz have been demonstrated for the first time in 2010-2011. Presently, their operating frequencies are getting close to 2 THz. The contemporary RTD oscillators can deliver ~0.5 mW at sub-THz frequencies and ~10 μW at THz frequencies. It was demonstrated that RTD oscillators could be as small as a fraction of mm^{2}, they consume low DC power and operate at room temperature. RTD oscillators have been used in high-speed wireless data-transmission experiments recently. In meanwhile, we understand better the physics of RTD limitations at very high frequencies, we could find the ways, how to overcome the limitations and novel types of RTD oscillators have been suggested.
We were concerned with the investigation of inherent limitation of RTDs and of relaxation tunnel processes (described by a time constant τ_{rel}) inside them. We have predicted that τ_{rel} is not limited by the tunnel lifetime (τ) of electrons in the quantum well of RTDs. It turns out that depending on the operating regime of RTDs, the relaxation processes could be much faster, as well as much slower than τ. We have also predicted that RTDs with unusually high doping in collector, should exhibit negative differential conductance at frequencies far beyond τ and τ_{rel} limits, i.e., when τω>>1 and τ_{rel}ω>>1. We have proved the effects experimentally up to ~600 GHz. Following further along this line of development, we could demonstrate oscillators working at ~1.1 THz in the regime τ_{rel}ω≈1 relying on RTDs with heavily doped collector and rather low current density. The analysis of the oscillators suggests that multi-THz frequencies should be achievable with RTD oscillators and the RTD oscillators have much room for further optimization.
Further on, we have brought the concept of an RTD with heavily doped collector to its logical limit: we have increased the collector doping to the extend, that the lowest quantum-well subband of the RTD stays immersed under collector Fermi level. In such RTDs, the electrons are injected into the quantum well not only from the emitter side (which is usual for RTDs), but also from the collector. The oscillators with such RTDs were demonstrated to be working at ~1.5 THz.
We have also analyzed theoretically the travelling-wave microstrip RTD oscillators. Such oscillators could be seen conceptually similar to THz quantum-cascade lasers (QCLs) with the metal-metal waveguide and with a single cascade period (an RTD) as their active core. However, contrary to THz QCLs, microstrip RTDs should be working at room temperature. Assuming realistic parameters of RTD layers (we took them from our past experimental studies) we show that microstrip RTD oscillators could be working up to ~1.5 THz. We expect that RTD layers specifically optimized for microstrip oscillators should extend the operating frequency even further.
In conclusion, there is much room for further development of RTDs and RTD oscillators, that should enable operation of RTD oscillators at multi-THz frequencies and increase their output power. RTD oscillators have potential to evolve into enabling technology for real-world THz applications

Erstellt aus der Publikationsdatenbank der Technischen Universität Wien.