| Summary: | 碩士 === 國立臺灣大學 === 光電工程學研究所 === 107 === One of the most important high frequency device is bipolar transistors (BJTs). The cut-off (fT) is limited for the thickness of base region so 2D materials is a great candidate as a material for base region for its ultra-thin thickness. Theoretically, vertical 2D material Hot Electron Transistors is seen to be a high potential device for potential Terahertz applications. It is like a bipolar transistor and there are regions, emitter, base and collector, too. Furthermore, there are two potential barriers. One is between base and emitter, tunneling oxide, and the other one is between collector and base, filtering oxide. The carriers can tunnel from emitter to base and then tunnel from base to collector. The carrier we use is hot electron which has high kinetic energy and high speed.
In this experiment, we use highly doped n-type silicon substrate as emitter, about 3 nm thickness native silicon dioxide (SiO2) as tunneling oxide, graphene as base, TiO2 (10 nm) and HfO2 (30 nm) as double layer filtering oxide and Titanium (Ti) as collector.
We are the first team to successfully demonstrate a graphene-based hot electron transistor with high frequency response. The device we fabricated remains high common-base current gain (α~0.96), high common-emitter current gain (β~18), high current density JC (~7 A/cm2) and the cut-off frequency (fT) achieves ~5.5 GHz.
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