Research Of Molybdenum Disulfide Phototransistor Based On Schottky Gate

Two-dimensional transition-metal dichalcogenides?2D TMDs?are considered to be a high potential candidate to apply in consumer electronics due to their atomic thickness,proper bandgap and ultra-high transport mobility.For typical wearable consumer electronics,they are eager to develop low threshold,fast operation and simplified fabrication process strategies.As the dielectric layer sacrifices the applied gate voltage and introduces interface defect,the reported 2D TMD metal-insulator-semiconductor field-effect transistors?MISFETs?usually suffer from high operating voltages and interfacial trap induced scattering.In order to avoid above problems,herein we developed 2D MoS₂-based Schottky-gated?SG?metal-semiconductor field-effect transistors?MESFETs?.Such devices highly relied on our new developed MoO_x/Au gate electrode.It also exhibited superior electrical performance and photodetection performance.The main work of the full thesis was summarized as follows:?1?In order to construct a reliable and stable Schottky-barrier,the gate materials of the MoS₂-MESFET optoelectronic device were selected and verified.At the beginning,the pure Au gate MESFET was fabricated,and then a high work function MoO_x was selected,but the results were not satisfactory.Finally,those two materials were combined to construct a MoO_x/Au Schottky-gate,and the resulting Schottky junction obtained a high On/Off ratio of10⁴.As a result,we have fabricated a reliable and stable Schottky barrier,which played a pivotal role in the MESFET devices.The built-in potential in the Schottky junction also has a unique role in separating photogenerated carriers.In this regard,the device was periodically irradiated by using a monochromatic LED laser with a wavelength of 530 nm.It was found that the Schottky built-in potential can effectively separate the photogenerated carriers,reduce their recombination probability,and accelerate the photodetection speed of the Schottky photodiode.?2?Then,the MoO_x/Au Schottky-gate 2D MESFET was tested and analyzed.In the dark condition,the On/Off ratio of MESFET reached 10⁵.The channel electron mobility was 160cm²V^-1s^-1 while the same channel back-gated?BG?MISFET only reached 6.9 cm²V^-1s^-1.The operating voltage of MESFET was in the range of few volts and the subthreshold swing was145 mV/dec,both of them were an order magnitude lower than MISFET ones.In the light condition,the photoresponse speed of the MESFET was 50 ms,while the photoresponse speed of MISFET was 200 ms.Finally,we implemented an inverter based on above MESFET as integrated prototype device.Its output exhibited a faster switching behavior and reached ten times voltage gain comparing to the mirrored inverter driven by MISFET.?3?Furthermore,we utilized the back electric field to tune the On-Off current,subthreshold swing and threshold voltage(V_th)of MESFET to adapt to different operation requirements.The subthreshold swing was tuned from 160 mV/dec to 130 mV/dec.And the threshold voltage was tuned from-3.5 V to-0.5 V.In addition,from the transfer curves,the SG and BG tuning demonstrated synergistic effects to further improve its on/off ratio by simultaneously sweeping V_SG and V_BG.When both the V_SG and V_BG were negative,the DG-FET device was more depleted and the off-state current reached to 10 pA.On the contrary,when both of them are positive,the channel is more active and the on-state current reached to 1.7?A.Besides of On/Off ratio improvement,the DG-FET had further improved its key SS value comparing with MESFET.Therefore,the synergistic effects from the SG and BG could be widely applied in various kinds of electronics to further enhance their performances.