Research Of Electrical And Photoelectronic Properties Of Monolayer MoS₂ Back Gate Field-Effect Transistors

The technology of semiconductor integrated circuit based on Si material developed rapidly,during the past half century.The transistors based on Si is gradually closing to the physical limited and “Post Moore Era” is coming.Two-dimensional layered crystalline materials with atomic-scale thickness have received intense interest in recent years.Bulk molybdenum disulfide?MoS₂?is a semiconductor with an indirect bandgap of 1.2 eV,while a monolayer of MoS₂ has a direct bandgap of 1.8 eV.Therefore,MoS₂ is a promising alternative to Si material to use in semiconductor devices.Besides,the photoelectric sensors,gas sensors and flexible devices based on MoS₂ are valuable in medical,environmental protection,mechanical and agriculture.The electronic and photoelectronic properties of supported and suspended MoS₂ FETs were studied with the supported of NSFC?No.51675246?.The monolayer MoS₂ films was fabricated by CVD method and transferred to the substrate with electrode,and the field effect transistors based on MoS₂ were performed.The optical microscope was used for the observation of the interconnection between MoS₂ and electrode,Raman spectrum for the representation of the layer and quality of MoS₂,and AFM for the representation of the surface and thickness of the samples.The transfer curves supported that the electron mobility of suspended MoS₂ FETs exhibited much higher than that of the supported devices at ambient temperature.The electron mobilities of both types of FETs increased at higher temperatures.The carrier mobility range of suspended FETs was much higher than that of supported devices.Coulomb scattering from charged impurities plays a crucial role in limiting charge transport.The mobility within the device was limited by Coulomb scattering at ambient temperature and surface/interface phonon scattering at higher temperatures.During the electrical measurement,large hysteresis was observed in the dual sweep test mode.The hysteresis of suspended device was much larger than that of supported device at room temperature,and the hysteresis increased with the rise of temperature.The adsorption of oxygen and water molecular on the surface of MoS₂ plays a crucial role in leading to the hysteresis,since the adsorbed molecular can capture charge carriers from the conduction band of the MoS₂ channel.Thermal annealing effect increased the injection of electrons via quantum tunneling through the Schottky barrier at the contact point,which caused higher hysteresis.The breakdown phenomenon was observed in the suspended devices as exist of the thin gate oxide.Many strained Si-O bonds exist in the interfacial layer and were easily broken,especially under high electric field.So the percolatio path formed at the moment of breakdown may consist of more traps near the substrate interface and the device was breakdown.The theory study of MoS₂ FETs has great guidance to practical application of transistors based on the MoS₂ films.