The Study Of Radio Frequency And Optoelectronic Devices Based On "Graphene On Germanium(GOG)" Substrates

The post-Moore era requires smaller,faster transistors,as well as more functional devices,such as radio frequency and optoelectronics.For RF transistors,it has always been the goal to continuously improve its cut-off frequency;optoelectronic devices need to continuously improve their detection performance before they can be applied to more precise detection occasions.Two-dimensional material electronic device is a new type of semiconductor device that is very promising to break through the limit of Moore’s Law.However,it is very difficult to fabricate large-area semiconductor devices based on two-dimensional materials,and it is difficult to integrate with mainstream silicon technology.The process of constructing large-area devices is the basis for the practical application of two-dimensional materials.In this paper,large-area silicon/graphene/germanium electron emission transistors and graphene-intercalated germanium electron emission transistors are fabricated based on graphene-ongermanium substrates.A large-area Si-Gr-Ge high-frequency transistor was fabricated by using grapheneon-germanium substrate,and the device performance was studied.The device can work in two different operating modes under different external bias conditions.When it works in thermionic emission transistor mode,the common base current gain of the device can reach 30%,which increases 30 times when it compared with the performance of previously reported Si-Gr-Ge transistors prepared from graphene grown by chemical vapor deposition method and then transferred.When it works in chargeemitting transistor mode,the common-emitter current gain of the device can reach about 1000 due to the quantum capacitance effect of graphene.This paper systematically studies the preparation and performance characteristics of Si-Gr-Ge transistors,which provides a new idea for the development of graphene transistors in the field of high-frequency devices.On the other hand,metal/germanium Schottky junction photodetectors have limited Schottky potential barrier height of the metal/germanium junction due to the small bandgap of germanium and the Fermi level pinning effect between metal and germanium,resulting in metal/germanium photodetectors have large dark currents with low sensitivity and signal-to-noise ratio.In this paper,graphene was inserted between germanium and metal to reduce the Fermi level pinning effect using a graphene-ongermanium wafer.A gold/graphene/germanium photodetector was fabricated.The wafer-scale graphene intercalation layer significantly increased the Schottky junction potential barrier height,resulting in a decrease in dark current to 1.6 mA/cm2 and a photodetector responsivity of 1.82 A/W,which is the best result for a metal/germanium Schottky junction photodetector.This excellent gold/graphene/germanium photodetector is expected to play its role in the field of optical communication.These results provide new ideas for the realization of high-performance RF devices and photodetectors,and a new method for the fabrication of large-area and silicon-based 2D material devices.