Study On Two-dimensional α-In₂Se₃ Ferroelectric Tunnel Junction

The rise of van der Waals ferroelectrics not only provides a new platform for the study of ferroelectricity in two-dimensional scale,but also has great potential in fields such as information storage and neural synapses.In known two-dimensional ferroelectrics,α-In₂Se₃is widely used in ferroelectric functional devices because of its semiconductor characteristics and unique in-plane and out of plane coupling ferroelectricity such as ferroelectric diodes,ferroelectric field effect transistors,ferroelectric semiconductor transistors and multi-channel memristors.However,the in-plane ferroelectric tunnel junction with low power consumption,non-destructive reading and multi-channel reading and writing characteristics is still in the stage of theoretical research.Limited by the micron-level in-plane resolution of electron beam exposure technology,this topic uses laser irradiation to fabricateβ/α/βIn₂Se₃in-plane ferroelectric tunnel junctions provides a new method for flexible multi-terminal nonvolatile ferroelectric memory.The main research contents are as follows:1.The phase transition regulation ofα-In₂Se₃by laser irradiation was explored.We studied the effects of laser power,substrate type and atmosphere on the laser irradiation ofα-In₂Se₃.We found that with the increase of laser power,In₂Se₃will gradually transform fromαphase toα,βmixed phase,pureβphase and amorphous phase.Combined with Raman spectroscopy,second harmonic and fluorescence spectroscopy,it is verified that high-qualityβ-In₂Se₃can be obtained in the 3m W power window.In addition,the substrate with low thermal conductivity is conducive to the phase transition,but the metal substrate may reduce the phase transition temperature and make the transition easier due to the effect of charge transfer.Therefore,,the phase transition mechanism also has the contribution of photogenerated carriers contribute in addition to Joule heating effect.2.Based on the above mild photoinduced phase transition scanning technology,we found that the conductivity of the same device improved with the increase of theβ-In₂Se₃volume through the step-by-step phase transition experiment.When the device was completely transformed into theβphase,The current value is increased by three orders of magnitude,demonstrating the good electrical conductivity ofβ-In₂Se₃.In addition,the nonlinear output curve ofα-In₂Se₃in direct contact with metal proves that theα-phase/metal interface is Schottky contact,while the linear output curve in theα-phase/β-phase/metal device indicates that ohmic contact is achieved.Therefore,it is proved that theβphase can be used as the electrode of theα-In₂Se₃in-plane device.3.In order to realize the in-plane tunneling effect,we fabricated high-precisionβ/α/βin-plane hetero-junctions by photoinduced phase transition.The unique in-plane structure can eliminate the resistance change caused by out of plane polarization antiparallel arrangement or polarization induced moving charge.We found that the conductivity of the device is related to in-plane polarization.The on-off ratio at room temperature exceeds 40 and increases to 270 when the temperature drops to 10 K,indicating that hot electron tunneling is the dominant conduction mechanism.Retention（10³seconds）and fatigue resistance（10³times）tests show that the device can be used as a non-volatile memory unit.Finally,we repeatedly fabricated several devices with good memory properties,which proves that photoinduced phase transition is a stable and precise means to fabricate high-qualityα/βIn₂Se₃in-plane heterojunctions.