Anwendung von Resonanz-Tunnel-Dioden oberhalb des Tunnellebensdauer-Limits und THz-Quellen auf der Basis der Dioden
Zusammenfassung der Projektergebnisse
Before the project has started, the highest reported fundamental frequencies of RTD oscillators were 712 GHz and 651 GHz. The record frequency (712 GHz) has been published in 1991 and no one could overcome the frequency in the subsequent ~20 years. It was not clear at that time, whether this is possible at all. Additionally, it was generally accepted that the tunnel electron lifetime (tau) in the quantum well between the barriers of an RTD determines the time scale of the relaxation processes inside RTDs and imposes a fundamental limitation on the operating frequencies of RTDs and RTD oscillators. Indeed, all RTD oscillators at that time were operating at frequencies below 1/tau. We have shown theoretically in the past that the relaxation processes inside RTD are determined by a different time constant, namely by a relaxation time (tau_rel), rather than tau. Due to Coulomb interaction between electrons, tau_rel deviates substantially from tau. Additionally, we have shown that it is possible to achieve negative differential conductance (NDC) at frequencies, which are far beyond the limits imposed by tau_rel and tau, i.e. at frequencies >>1/tau_rel and >>1/tau. NDC at so high frequencies is achievable in special RTDs with heavily doped collector. Before the project, we have also demonstrated the above effects experimentally at relatively low frequencies up to 12 GHz. The objectives of the project were, first, to demonstrate that the same effects are working at much high frequencies. Second, we wanted to demonstrate that RTD oscillators can also operate at frequencies >>1/tau_rel and >>1/tau. Third, we wanted to overcome the record frequency of 712 GHz and to demonstrate THz RTD oscillators. All these objectives have been achieved in the course of the project. In the first phase of the project, we have realized a set of RTD oscillators with frequencies ranging from 18 GHz to 150 GHz. The oscillations have been achieved at the frequencies 3 times higher than1/tau and 10 times higher than 1/tau_rel. In the second phase of the project, we have realized and investigated several RTD oscillators operating at frequencies 388-564 GHz. Our oscillators were working at the frequencies 1.2 times higher than1/tau and 2.6 times higher than 1/tau_rel at 564 GHz. Theoretical analyses of the measurement results shows that RTDs should be capable of oscillating up to approximately 800 GHz. Then the frequency would be 1.7 times higher than1/tau and 3.7 times higher than 1/tau_rel. The frequency closest to 1/tau reported in the literature in the past was still a factor of 0.7 below 1/tau at 38 GHz. Therefore, the above results are the first ever reports of RTD oscillators operating at frequencies above 1/tau. We prove experimentally, that it is possible to overcome the tunnel-lifetime limit of RTDs. Additionally, operation of an RTD oscillator at a certain frequency is a direct proof that the RTD has NDC at the given frequency. In such a way, we prove that our RTDs with heavily-doped collector have NDC at frequencies >1/tau and >>1/tau_rel. These experimental results fully support our previous theoretical predictions. Further, we have increased the operating frequency of our RTD oscillators above 1.1 THz and have set a new world record for the operating frequencies of RTD oscillators. Our RTDs set also a record operating frequency for all kinds of active semiconductor devices nowadays. Additionally, we show, that much higher operating frequencies of RTDs and RTD oscillators should be achievable. The frequency of 1.1 THz is approximately equal to 1/tau_rel for our RTD oscillators, but our study shows that operation of RTDs beyond the relaxation-time and tunnel-lifetime limits at THz frequencies should be possible. We expect the frequencies of 2 - 3 THz to be achievable with RTD oscillators. The size of our THz RTD oscillators is extremely small: it is only 0.5 x 0.5 mm^2. Additionally, such THz sources are relatively simple, they work at room temperature and just a simple voltage source is required for their operation. There is no other THz source nowadays, which can combine such properties. Such THz sources should enable plenty of applications.
Projektbezogene Publikationen (Auswahl)
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Demonstration of RTD oscillations beyond tunnel-lifetime limit. 35th Workshop on Compound Semiconductor Devices and Integrated Circuits, WOCSDICE 2011, Catania, Italy, May 29 - June 1, 2011, pp. 47-48.
C. Sydlo, M. Feiginov, O. Cojocari, P. Meissner
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High-frequency nonlinear characteristics of resonant-tunnelling diodes. Appl. Applied Physics Letters, Vol. 99. 2011, Issue 13, 133501.
M. Feiginov, C. Sydlo, O. Cojocari, P. Meissner
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On the Inherent Limitations of RTD Oscillators: Operation Beyond Tunnel-Lifetime Limit. 17th Int. Conf. on Electron Dynamics in Semiconductors, Optoelectronics and Nanostructures, EDISON17, Santa Barbara, California, USA, August 8-12th, 2011.
M. Feiginov, C. Sydlo, O. Cojocari, P. Meissner
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Operation of resonant-tunnelling oscillators beyond tunnel-lifetime
EPL (Europhysics Letters), Vol. 94. 2011, Number 4, 48007.
M. Feiginov, C. Sydlo, O. Cojocari, P. Meissner
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Resonant-tunnelling-diode oscillators operating at frequencies above 1.1 THz. Applied Physics Letters, Vol. 99. 2011, Issue 23, 233506. (Selected as a research highlight by APL and belongs to 20 most-read articles in December 2011)
M. Feiginov, C. Sydlo, O. Cojocari, P. Meissner
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Operation of resonant-tunnelling-diode oscillators beyond tunnel-lifetime limit at 564 GHz. EPL (Europhysics Letters), Vol. 97. 2012, Number 5, 58006.
M. Feiginov, C. Sydlo, O. Cojocari, P. Meissner
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RTD-based THz-MIC by Film-Diode Technology. IMS2012 International Microwave Symposium, Montréal, Canada, June 17-22, 2012.
O. Cojocari, C. Sydlo, M. Feiginov, P. Meissner
