Abstract
Graphene-base transistors have been proposed for high-frequency applications because of the negligible base transit time induced by the atomic thickness of graphene. However, generally used tunnel emitters suffer from high emitter potential-barrier-height which limits the transistor performance towards terahertz operation. To overcome this issue, a graphene-base heterojunction transistor has been proposed theoretically where the graphene base is sandwiched by silicon layers. Here we demonstrate a vertical silicon-graphene-germanium transistor where a Schottky emitter constructed by single-crystal silicon and single-layer graphene is achieved. Such Schottky emitter shows a current of 692 A cm−2 and a capacitance of 41 nF cm−2, and thus the alpha cut-off frequency of the transistor is expected to increase from about 1 MHz by using the previous tunnel emitters to above 1 GHz by using the current Schottky emitter. With further engineering, the semiconductor-graphene-semiconductor transistor is expected to be one of the most promising devices for ultra-high frequency operation.
Highlights
Graphene-base transistors have been proposed for high-frequency applications because of the negligible base transit time induced by the atomic thickness of graphene
For a bipolar junction transistor (BJT), a main figure of merit is the alpha cutoff frequency fα, which is used to represent the upper frequency limit when a BJT is biased in the common base mode. fα is inversely proportional to the delay time, which includes the emitter charging time τe, the base transit time τb, and the collector delay time τc[2,3,4,5]
For the hot electron transistors, when an electron is emitted into the base, the energy difference between the electron and the Fermi energy level of the base is transformed into electron kinetic energy
Summary
Graphene-base transistors have been proposed for high-frequency applications because of the negligible base transit time induced by the atomic thickness of graphene.
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