整合光柵結構與電晶體的室溫兆赫波輻射源之研究

Abstract

本論文研究電激發下的InGaAs/GaAs multi-finger pHEMT在兆赫波段的輻射特性與其背後物理機制。藉由改變結構參數，如元件尺寸、finger數目、電極的金屬覆蓋率以及散熱空間存在與否，量測並探討比較其輻射強度、輻射場型、偏振特性及頻譜的變化。我們發現元件操作於飽和區會有較高的輻射功率轉換效率。元件的輻射強度會因散熱空間的存在而降低。當元件尺寸變小時，其輻射場型大角度的成份會增加。此外，輻射訊號的偏振度與元件尺寸及金屬覆蓋率成正相關變化，且其偏振度會隨偏壓而改變。透過觀察上述現象與輻射頻譜，我們推論兆赫輻射來自於聲子，並且輻射特性與聲子激發的效率、聲子的數目及聲子的穿播方向息息相關。

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.