Operation of resonant-tunnelling diodes (RTDs) beyond tunnel-lifetime limit and THz sources on the basis of the diodes

我们在过去已经从理论上预测，RTD的工作频率既不受其隧道寿命（tunnel life time）限制，也不受隧道弛豫时间（tunnel relaxation time）限制，并且适当设计的RTD在远远超过两个时间常数所施加的限制的频率处应该具有负微分电导，即，RTD振荡器应该可以实现超过这些限制。几年前，我们已经在12 GHz以上的频率上对理论预测进行了实验验证。在本项目的第一阶段，我们已经演示了RTD振荡器，在109 GHz的ω ε高达3.0和ω ε rel高达6.8，到目前为止，最高振荡频率为150 GHz。该项目第二阶段的目标是证明RTD振荡器也可以在太赫兹频率下工作，在ω rel> 1和ω> 1的范围内，甚至在ω rel>> 1和ω>> 1的范围内。基本上，目的是学习如何使RTD以尽可能高的频率（特别是在THz范围内）振荡，以及如何为此正确设计RTD。这也应该导致我们实现的太赫兹振荡器的工作频率超过目前的技术水平（831 GHz）。我们相信，这一目标将在项目第二阶段实现。一方面，我们项目的主题是围绕澄清RTD的基本限制的问题，它也与其他相关的电子器件，如多势垒结构，量子级联激光器，单电子晶体管等有关。另一方面，该主题具有很强的应用导向成分。作为我们项目的一个成果，一个非常紧凑的太赫兹源的关键技术出现。我们正在研究的太赫兹源的尺寸可能是亚毫米级，而且可能很便宜。这种类型的源可以彻底改变某些类型的THz应用。例如，在一个示例中，这种源的技术将是用于紧凑型THz传感器、光谱仪等的使能技术。不存在非常紧凑和简单的THz源。这对太赫兹技术可能应用的所有领域都很重要：汽车工业、医药、生物技术、产品质量控制、安全、军事、通信等。

We have predicted theoretically in the past, that the operating frequencies of RTDs are limited neither by their tunnel life time () nor by the tunnel relaxation time (rel) and that properly designed RTDs should have negative differential conductance at the frequencies far beyond the limits imposed by both time constants, i.e., the RTD oscillators should be realizable beyond those limits. The experimental demonstration of the theoretical predictions at the frequencies up 12 GHz has been done by us several years ago. In the first phase of the present project, we have already demonstrated the RTD oscillators with ω up to 3.0 and ωrel up to 6.8 at 109 GHz and the highest oscillation frequency was 150 GHz till now. The aim of the second phase of the project is to demonstrate that RTD oscillators can work also at THz frequencies in the regime ωrel >1 and ω>1 and even in the regime ωrel >>1 and ω>>1. Basically, the aim is to learn how to bring the RTDs to oscillations at their highest possible frequency (particularly in the THz range) and how to design the RTDs properly for that. That should also lead us to realization of the THz oscillators with the operating frequency beyond the present state of the art (831 GHz). We are convinced that this goal will be achieved in the second phase of the project. On one hand, the subject of our project is turning around the issue of clarifying the fundamental limitations of RTDs and it is relevant also to other related electronic devices, like, multi-barrier structures, quantum-cascade lasers, single-electron transistors, etc. On the other hand, the subject has a strong application oriented component. As an outcome of our project an enabling key technology for extremely compact THz sources emerges. The THz sources we are investigating could be sub-mm in dimensions and also potentially cheap. Such kind of sources can revolutionize certain types of THz applications. E.g., the technology of such sources would be an enabling technology for compact THz sensors, spectrometers, etc. No comparably compact and simple THz sources exist. That could be important for all the fields, where THz technology might find application: auto-industry, medicine, biotechnology, product quality control, security, military, communication, etc.