在發展THz 電晶體時，藉由能帶結構設計以提高元件的電流密度及電流增益截止頻率是一個重要的方式。本實驗室在前年提出一種以銻砷化銦鎵(InGaAsSb)為基極的新型異質接面雙載子電晶體，此種電晶體不但具有超低的開啟電壓，亦有優秀的高頻特性。本論文專注於探討此種電晶體中，銻砷化銦鎵基極材料對於元件電流增益截止頻率，最大電流密度，以及載子傳輸特性的影響。
本研究成功地製作了射極面積為1×10 μm2 的小元件，其電流增益截止頻率為222 GHz，最大電流密度為576 kA/cm2，與傳統的砷化銦鎵單異質接面雙載子電晶體比較(217 GHz，372 kA/cm2)，有明顯的優勢。經由小訊號參數分析，可萃取得到此電晶體基極的電子擴散係數(Dn)約為95.7cm2/s，其集極平均速度高達3.2×107 cm/s，約為傳統砷化銦鎵單異質接面雙載子電晶體的1.28 倍，證實了此電晶體之優越性。
此研究也包含了觀察不同銻含量之銻砷化銦鎵基極對元件的影響。利用順向與逆向Gummel-plot 量測可以得知，增加銻含量所造成基-集極接面能帶的改變，能夠更進一步提高元件之最大電流密度與集極平均速度，而獲得更優秀的高頻特性。
總之，此研究不但成功地完成1 μm 射極元件之製作，並且利用各種直流及交流量測技術，深入分析載子傳輸特性，為InP/InGaAsSb 異質接面雙載子電晶體之設計與應用提供了重要的指引。

Bandgap engineering is an important and effective way to increase thecurrent density and current gain cut-off frequency (fT) in the development of THz transistors. The year before last, a new heterojunction bipolar transistor
(HBT) with InGaAsSb base was proposed and demonstrated by our group. This novel transistor has not only ultra-low turn-on voltage but also excellent high-frequency performance. In this work, efforts are focused on systematicstudy on the effects of this InGaAsSb base on the current gain, cut-off frequency,maximum current density, and carrier transport of the transistor.
Devices with 1x10 μm2 emitter finger are fabricated in this work. Their fTand maximum current density is 222 GHz and 576 kA/cm2, which is superiorthan the 217 GHz and 372 kA/cm2 observed on the conventional InP/InGaAssingle HBTs. Through detailed analysis on the measured small signal parameter,the electron diffusion coefficient (Dn) is determined to be 95.7 cm2/s and the average electron velocity in collector is 3.2x107 cm/s, which is 1.28 times that of the conventional InP/InGaAs single HBTs and confirms the superiority of this novel transistor.
In this work, the effect of Sb composition in the base on the device performance is also investigated. Through forward and reverse Gummel plot measurements, it is concluded that higher Sb content leads to higher current
density and collector average velocity for the devices studied.
In conclusion, 1 μm devices have been fabricated and characterized by both dc and ac measurements, which reveal the carrier transport properties of InP/InGaAsSb HBTs. The results obtained in this work provide several critical
guidelines for the design and application of this novel transistor.

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