Research On Memory Performance And Hysteresis Mechanism Of Novel MoS₂/GeSe₂ Heterojunction

Since graphene was successfully prepared,two-dimensional materials have been widely studied due to their excellent properties.Due to the surface sensitivity of two-dimensional materials,the hysteresis phenomenon caused by many factors,such as surface adsorbate,dielectric layer and its own defects,are commonly observed.Although the hysteresis reduces the performance of the device in most of cases,it is favored in the field of memory applications.Through some methods like surface modification,defect regulation and structure design,the hysteresis could be enhanced and provides new vitality for the application of two-dimensional materials in the memory field.And according to these methods,a variety of memory structures,such as surface-modified transistor memory,resistive random access memory,ferroelectric memory and floating gate memory,have gradually demonstrated the excellent performance and application potential of two-dimensional memories.In this context,this paper used the MoS2 and new binary ?-? chalcogenide GeSe2 to fabricate a novel type of memory device with MoS2/GeSe2 vertical heterojunction,and then explored its hysteresis effect and working mechanism deeply.At first,we successfully grew high-quality MoS2 and GeSe2 bulk crystals by the chemical vapor transport method.Then,using PDMS-assisted mechanical exfoliation method,we obtained thin layers of MoS2 and GeSe2 with the lateral size of tens of microns.We also confirmed the good lattice structure and electrical properties of the obtained MoS2 and GeSe2 materials through the characterization of X-ray diffraction,Raman spectroscopy and MoS2 field effect transistor.After that,we fabricated the novel memory device based on MoS2/GeSe2 vertical heterojunction on a thin HfO2 substrate by the PDMS-assisted dry transfer method.The device shows a huge memory window of about 10V under the gate range of+/-10V.And in the tests of time stability and cycle stability,the device still maintained a write/erase ratio of more than 102 after 2× 103s and 103 cycles,which indicates the good performance of the device.Next,we designed two different structures of MoS2/hBN/HfO2 and MoS2/GeSe2/hBN for comparison to explore the source of enhanced hysteresis,and drew a preliminary conclusion that it mainly lies in the MoS2/GeSe2 vertical heterojunction.In order to obtain a futher understanding of the hysteresis and working mechanism,we have conducted a deep research and analysis of MoS2/GeSe2 heterojunction from many perspectives such as gate dependence,scan rate,time constant,temperature dependence and photo response.According to the above results,we propose a model that the hysteresis is caused by gate induced charge transfer process which is dominated by thermal emission.And it gives a reasonable explanation for the working cycle of the device and the obtained experimental phenomenon.In summary,we have proposed a new structure of two-dimensional memory device which is based on MoS2/GeSe2 vertical heterojunction,and it showed good memory performance.Through further exploration,we proposed a reasonable hysteresis model to deeply understand and explain the experimental phenomenon and working mechanism.It is thought that this will provide new ideas and help for the improvement of memory performance and the design and exploration of other new memory structures.