Research On Hot Electron Devices Based On Two-dimensional Materials

The traditional Si based transistors will eventually encounter its physical limit as the transistors continuously scale down.There are extensive research on devices based on new materials and new structures,which are expected to be an alternative to the next generation of electronics.Two-dimensional?2D?materials draw lots of attention due to their superior property on electrical,optical and mechanics,and?opto-?electronics based on 2D materials show enormous potential on outperforming traditional devices.This thesis,focusing on the hot carriers in 2D materials,demonstrates the design of all-two-dimensional-material hot electron transistor?HET?and broadband charge-coupled device?CCD?based on hot electron injection mechanism.Firstly,we investigated the basic electrical and opto-electrical properties of two-terminal van der Waals heterojunction.We found that the mixed mechanism of thermal emission and tunneling dominate in the graphene?Gr?/WSe₂/Gr junction at room temperature,and FN tunneling dominate in the higher barrier Gr/hBN/Gr junction.Secondly,we prepared HETs based on the Gr/WSe₂/Gr/WSe₂/Gr symmetric structure,in which we realized the control of hot electron injection and collection.The device showed similar performance before and after exchange the role of emitter and collector,and background current was reduced by using thicker WSe₂ as the collector barrier.After optimization we achieved 90%collection efficiency.Thirdly,by replacing one WSe₂ layer with larger-bandgap hBN,we prepared asymmetric HETs based on the Gr/hBN/Gr/WSe₂/Gr.We found that using higher barrier to inject and lower barrier to collect carriers benefit to the high collection efficiency.But high injection energy may make the device difficult to turn off,which can be solved by using thinner hBN.A theoretical model was proposed to explain the output curves under positive and negative emitter bias.Record-high collection efficiency approaching theoretical limit and output current density of 400 A/cm² with good saturation were realized in the asymmetric HETs.Lastly,we fabricated charge-injection devices based on the single-layer graphene?SLG?/SiO₂/Si/multi-layer graphene?MLG?structure.We use MLG to absorb infrared?IR?light,and inject IR light excited hot carriers from the MLG into the deep-depletion well of Si.The photo-charges were integrated in the Si potential well similar to traditional CCD,and finally read-out by the SLG through field effect.We broaden the detection band of Si CCD to 4?m using the hot carrier injection function.A broadband detection covering visible to mid-IR was realized at room temperature in this device.Those results show that?opto-?electronics based on 2D materials could break the limits of traditional devices thanks to the unique properties of 2D materials.The integration of 2D materials with Si platform could combine the advantages of both.Those results explore the new generation of electronics and open new opportunities for the application of 2D materials.