Study Of Interface Control And Optoelectronic Performance Based On MoS₂ Transistors

With the continuous improvement of chip integration,it becomes more and more difficult to downsize the traditional silicon-based transistors.On one hand,the thickness of traditional silicon-based transistors have approached their physical limits,and the technology is hard to break through the difficulties.On the other hand,the resulting short channel effect and dielectric tunneling increase static power consumption and calorific value of the chip,which affect the reliability and stability of the device.It is urgent to find new materials to replace the silica-based material to further reduce the characteristic size of the transistors and improve the integration of the chips.Compared with traditional silicon-based semiconductor materials,two-dimensional semiconductor materials have an atomic-level thickness,which is easier to realize the transport and regulation of carriers by the applied electric field.Besides,their smooth surface can effectively alleviate the short-channel effect of transistors and facilitate the high-speed development of small-size semiconductor devices.MoS₂,as a typical two-dimensional semiconductor material,has a suitable bandgap and has an excellent application prospect in low power consumption and high switching ratio devices.Therefore,as the semiconductor devices in the post-silicon era,MoS₂-based electronic devices and photoelectric devices have been widely studied.MoS₂field-effect transistors(FETs)have many disadvantages,such as high hysteresis,high operating voltage,high contact resistance,which limit its development in the field of electronic devices and photoelectric devices.To improve the performance of MoS₂FETs,the study works on the optimization of gate/channel interface and metal electrode/channel interface of MoS₂ FETs,as well as the construction of MoS₂heterojunction,which is as follows.(1)To solve the problems of the instability for the transistors with high-k dielectrics and the hysteresis and high operation voltage for the transistors with low-k dielectrics,we prepared MoS₂ FET with high-k/low-k(P(VDF-Tr FE)/PMMA)dielectrics.This device shows free hysteresis for the interface state density of the device as low as 7.0×10¹¹ cm^-2·e V^-1 and can switch on/off state under the operating voltage of less than 4V.Moreover,the performance of the device can remain stable in the gate bias stress test and 101-cycle stability tests.The bilayer dielectric engineering strategy provides a potential method to realize the free-hysteresis and low power consumption operation of two-dimensional transistors with high stability.(2)Ni and Cr,as common metal electrodes,not only have high work function but also can cause MoS₂crystal structure distortion when they were deposited on the surface of MoS₂.This deposition process could introduce unnecessary defects in MoS₂and lead to the serious Fermi level pinning effect,thus greatly reducing MoS₂ device performance.Therefore,liquid-metal Ga and Sn with low work function were used as contact metal electrodes of MoS₂ FET,contributing to prepare MoS₂ transistors with excellent performance.Due to Ga with a low work function of 4.32 e V,the Schottky barrier in the Ga/MoS₂ interface is only 36.7 me V,resulting in reducing contact resistance of the MoS₂ transistor.The minimum contact resistance of the MoS₂transistor is about 1.84 K??m.Besides,the surface of MoS₂ was not damaged after depositing Sn on the surface of MoS₂,enabling its mobility up to 81.9 cm²/V S.The work explored the electrical properties of MoS₂ FFT with low-work-function liquid-metal contact and broadened the selection of metal electrode suitable for MoS₂ FFT.(3)To reduce the distance of transverse transmission channel in MoS₂/WSe₂heterojunction and improve the efficiency of absorbing photon-generated carrier by electrodes,black phosphorus was inserted into the MoS₂/WSe₂ heterojunction to build the MoS₂/BP/WSe₂ vertical heterojunction,and graphene was used as the electrode to place the upper and lower ends of the vertical heterojunction.The research results show that the structure destroys the original PN structure and fails to form the built-in electric field,and its action mechanism is the photoconductivity effect,not the photovoltaic effect,resulting in the photoelectric performance of the heterojunction device far from reaching the expected level.Under the light source with the wavelength of 532 nm and the light intensity of 421 m W/cm²,the maximum photoresponsivity and photo detectives are 58.1 m A/m V and 6.9×10⁸ Jones,respectively,and the rising current time is 5.7 ms,which were superior to the photoelectric property of the devices with a single two-dimensional material.