Research On Quantum Dot Based Vertical Field Effect Phototransistors

Recently,solution processed materials have been greatly investigated for the large area and easy integration infrared photo detectors due to their advantages in low cost,flexibility and easy processing.The improvement of the preparation process of the solution processed materials as quantum dots(QDs)and polymers have significantly improved the photo performance of the solution processed field effect photo transistors(FEp Ts).To further enhance the photo performance of the QD based FEp Ts,new architecture design and processing technology are required.The channel length of the lateral FEp Ts(LFEp Ts)is limited in micrometer scale by the standard photolithography process,which extends the carrier transit time.The carrier transit time can be reduced in short channel,which is benefit for high gain.Determined by the thickness of the photo sensitive layers,the channel length of the Vertical FEp Ts(VFEp Ts)can be downscaled to nanometer scale by the spin-casted method,which can reduce the complexity of the fabrication process.Unnecessary waste is avoided.In this paper,we have researched the photo performance of the solution processed QDs and P3HT/QDs hybrids VFEp Ts,in which the Au/Ag nanowire nets have been applied for the transparent source electrode.We have further studied the influence of the channel length on the photo performance of the QDs based VFEp Ts.The dissertation mainly includes the following three aspects.1.We have studied the photo performance of the short channel QDs based VFEp Ts,which apply situ self-assembed solution processed Au/Ag nanowires nets as transparent source electrode.The source drain current was modulated by the gate voltage through the perforations between the Au/Ag nanowires.The channel length was downscaled to 260 nm through the spin casted method.As a result,the device could be operated on the source-drain and gate voltages of-1 V and exhibited high photo performance.Under the illumination of the 808 nm laser with light irradiance of 1.25 m W/cm2,the device showed photo responsivity of 2×104 A/W and photo detectivity of 7×1012Jones.2.We have studied the influence of the channel length on the photo performance of the VQFEp Ts.We have fabricated five devices with different channel length by spin casted method.Through the photoelectric measurement,we found that the device with channel length of 980 nm shown best photo performance.Under the illumination of the 808 nm laser with light irradiance of 1 m W/cm2,the device exhibited high photo responsivity of 1 × 105 A/W and high photo detectivity of 1.2×1013 Jones.3.We have studied the photo performance of the P3HT/Pb S QDs layered heterjunction based VQFEp Ts.Combining the advantages of the layered heterojunction and the short channel length(500nm),the photo sensitivity of the vertical architecture device was improved remarkably.The device can be operated under the source drain and gate voltages of-1 V,and the photo response time was as short as 9 ms.Under the illumination of the 808 nm laser with light irradiance of 1 m W/cm2,the device exhibited high photo responsivity and high photo detectivity of 9×104 A/W and 2×1013 Jones respectivly.