| Summary: | 碩士 === 國立交通大學 === 電子研究所 === 100 === This paper investigates the characteristics and the underlying physics of radiation from electrically excited InGaAs/GaAs multi-finger pHEMTs at terahertz frequencies. We measured the radiation intensity, radiation pattern, the degree of polarization of the radiation, and the radiation spectra of pHEMTs as functions of structural parameters, such as device sizes, number of fingers, the filling factor of grating–like electrodes and the presence of a heat sink. Experimental results show that a pHEMT has higher radiation power conversion efficiency while operating in saturation region. A pHEMT has lower radiation intensity with the presence of a heat sink. The radiation pattern shows enhanced large-angle components while reducing the size of a pHEMT. The degree of polarization is directly proportional to the size of a pHEMT and the filling factor; it also varies with biases. By observing radiation spectra along with the above results, we infer that the terahertz radiation comes from phonons. Furthermore, radiation characteristics depend strongly on the excitation efficiency, the number, and the propagation direction of phonons.
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