In 1947, the first transistor, a bipolar junction transistor (BJT), was invented in the Bell Laboratory and has since led to the age of information technology. In recent decades, there has been a persistent demand for higher frequency operation for a BJT, leading to the inventions of new devices such as heterojunction bipolar transistors (HBT) and hot electron transistors (HET). The HBTs have enabled terahertz operations, but their cut-off frequency is ultimately limited by the base transit time; for the HETs, the demand of a thin base without pinholes and with a low base resistance usually causes difficulties in material selection and fabrication.
Recently, researchers have proposed graphene as a base material for transistors. Because of the atomic thickness, the graphene base is almost transparent to electron transport, leading to a negligible base transit time. At the same time, the remarkably high carrier mobility of graphene will benefit the base resistance compared with a thin bulk material. Graphene-based transistors (GBTs) generally use a tunnel emitter that emits an electron through an insulator. However, the emitter potential barrier height seriously limits the cut-off frequency. Theoretical study has indicated that a Schottky emitter may solve this potential barrier limitation.
A team of researchers at the Institute of Metal Research, Chinese Academy of Sciences, has built the first graphene-based transistor with a Schottky emitter, which is a silicon-graphene-germanium transistor. Using a semiconductor membrane and graphene transfer, the team stacked three materials including an n-type top single-crystal Si membrane, a middle single-layer graphene (Gr) and an n-type bottom Ge substrate.
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