Theoretical Analysis of Terahertz Detection of Resonant Tunneling Diodes

We analyze the terahertz detection characteristics of resonant tunneling diodes (RTDs) using a set of simple equations that covers three detection modes; (i) direct detection, (ii) amplified detection, and (iii) self-homodyne (coherent) detection. (i) and (ii) are based on the square-law detection, and (iii) is on the homodyne detection with the RTD used as an injection-locked local oscillator. The calculated results exhibit small- and large-signal areas depending on irradiation power. In the small-signal area, the detection current is proportional to irradiated power for (i) and (ii), and to square root of irradiated power for (iii). The detection current has a peak at the bias voltage at the boundary between (ii) and (iii). Effect of frequency fluctuation of irradiated wave is analyzed for (iii), and it is shown that the detection current is proportional to irradiated power if the fluctuation becomes wider than injection-locking range. The analytical results in this paper reasonably explain the reported experiments.Comment: 6 pages, 5 figure

Simple model for frequency response of a resonant tunneling diode caused by potential change of quantum well due to electron charge

The frequency dependence of negative differential conductance (NDC) is an important property for the resonant-tunneling-diode terahertz source. Among several phenomena determining the frequency dependence, this paper shows that the effect of potential change of the quantum well due to electron charge can be analyzed with a simple and tractable model based on the tunneling admittance and capacitance. The result is identical to that of Feiginov's analysis based on more fundamental equations, showing a one-to-one correspondence between the parameters of the two analyses. Similar to Feiginov's analysis, our analysis also shows that NDC remains finite even at infinitely high frequency. It is shown in our model that this result is attributed to neglecting the tunneling time at the emitter barrier. Comprehensive analysis of the frequency dependence of NDC will be possible by incorporating the tunneling time into the present model.Comment: 5 pages, 2 figure

Novel resonant-tunneling-diode terahertz oscillators and applications

The recent progress in resonant-tunneling diode (RTD) THz oscillators and applications is reviewed. For high-frequency and high output power, RTD oscillators integrated with cylindrical and rectangular cavities have been developed. Structure simplified RTD oscillators for easy device fabrication and good uniformity were proposed and fabricated. This simple structure has an extensibility for large-scale array, active metamaterial, and beam forming function. Novel THz radar systems using RTD oscillators were proposed, and a precise distance measurement and a three-dimensional imaging were demonstrated

Terahertz Emitter Using Resonant-Tunneling Diode and Applications

A compact source is important for various applications utilizing terahertz (THz) waves. In this paper, the recent progress in resonant-tunneling diode (RTD) THz oscillators, which are compact semiconductor THz sources, is reviewed, including principles and characteristics of oscillation, studies addressing high-frequency and high output power, a structure which can easily be fabricated, frequency tuning, spectral narrowing, different polarizations, and select applications. At present, fundamental oscillation up to 1.98 THz and output power of 0.7 mW at 1 THz by a large-scale array have been reported. For high-frequency and high output power, structures integrated with cylindrical and rectangular cavities have been proposed. Using oscillators integrated with varactor diodes and their arrays, wide electrical tuning of 400–900 GHz has been demonstrated. For spectral narrowing, a line width as narrow as 1 Hz has been obtained, through use of a phase-locked loop system with a frequency-tunable oscillator. Basic research for various applications—including imaging, spectroscopy, high-capacity wireless communication, and radar systems—of RTD oscillators has been carried out. Some recent results relating to these applications are discussed