| Summary: | 碩士 === 國立中央大學 === 電機工程研究所 === 96 === 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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