Emerging Non-layered Two-dimensional Material In₂S₃:Material Growth,Device Fabrication And Photo-response Characteristics

In the information age,photodetectors operating in a photovoltaic mode with fast response speed and low power consumption make them superior candidates for applications in extensive fields,such as optical communications,environmental monitoring and industrial safety.Mo S₂-like nanomaterials have become an emerging research direction in the past decade due to their unique material properties.When one dimension of a material is below 100 nm and carriers can move freely in the space of two dimensions,many excellent properties are distinguished from the bulk material.Such materials are called two-dimensional materials.To date,the mainstream research of two-dimensional materials is two-dimensional layered materials,which have good application prospects in the field of micro-nano processing.Its low dark current and faster transmission channel break through the bottleneck of traditional three-dimensional materials which exhibit poor responsivity.In contrast,the emerging non-layered two-dimensional materials in recent years have extremely high compatibility with the current mature semiconductor micro-nano processing technology due to the existence of dangling bonds on the surface.The research and application of this kind of materials have been paid lots of attention.As an emerging IIIA-VIA semiconductor,In₂S₃ exhibits great potential for application in optoelectronics.In this thesis,the physical vapor phase epitaxy of two-dimensional non-layered material In₂S₃ is studied,and a series of high-performance photodetectors are fabricated based on the excellent optical properties of In₂S₃.The specific work is as follows:1.Large-scale and high-crystalline In₂S₃ flakes were prepared by physical vapor phase epitaxy(PVE).Herein,the thickness of ultrathin non-layered In₂S₃ nanoflake is about 20 nm with lateral size up to 161?m.Moreover,the optical microscopy,Raman,PL,XRD,TEM,XPS,atomic force microscope and other tests are introduced to proved the high crystallinity of the In₂S₃ nanoflake.2.Stacking n-type In₂S₃ and p-type graphene to form a van der Waals heterostructure.The stacking of these two materials can produce an atomically sharp interface with van der Waals interaction,which may lead to high performance in(opto)electronics.In this study,we fabricated a van der Waals heterostructure composed of In₂S₃ and graphene via the dry transfer method.Scanning Kelvin probe force microscopy revealed a significant potential difference at the interface of the heterostructure,thereby endowing it with good diode characteristics.The back-gate field effect transistor based on the graphene/In₂S₃ heterostructure exhibited excellent gate-tunable current-rectifying characteristic with n-type semiconductor behavior.A photodetector based on the graphene/In₂S₃ heterostructure showed excellent response to visible light.Particularly,an ultrahigh responsivity of 795 A/W and an external quantum efficiency of 2440%are recorded under the illumination of 405 nm light and can be further increased to 8570 A/W and 26200%with a positive gate voltage of 60V.The excellent optical responsive performance is attributed to the synergy of photoconductive and photogating effects.These intriguing results suggest that the graphene/In₂S₃ heterostructure has prospective applications in future electronic and optoelectronic devices.3.In₂S₃/Si heterojunction photodetector was prepared by combining n-type In₂S₃ and p-type Si.Owing to the strong light-matter interactions of In₂S₃ and the built-in potential at In₂S₃/Si interface,which accelerates the separation of photoexcited electron-hole pairs,the device exhibits a broadband sensitivity covering the visible to near-infrared.The responsivity,detectivity and rise/decay time are 579.6A/W,2×10¹¹ Jones and 9/0.131 ms,respectively.These performance metrics are among the best values comparing with reported layered 2D materials/Si heterojunction photodetectors.Notably,the In₂S₃/Si photodetector suffers negligible performance degradation even after 1050 cycles of operation or 6 months exposure to air.These findings broaden the scope of 2D materials and highlight that In₂S₃nanoflakes hold great potentials for further optoelectronic applications.4.A novel strategy for coupling 2D In₂S₃ with Gr/Si PDs is demonstrated.The introduction of double-heterojunctions design not only strengthens the light absorption of graphene/Si,but also combines the advantages of photogating effect and photovoltaic effect,which suppresses the dark current,accelerates the separation of photogenerated carriers and brings photoconductive gain.As a result,the In₂S₃/graphene/Si device presents ultrahigh photoresponsivity of 4.53×10⁴ A/W and fast response speed less than 40?s,simultaneously.These parameters are an order of magnitude higher than pristine Gr/Si PDs and among the best values comparing with reported 2D materials/Si heterojunction photodetectors.Furthermore,the In₂S₃/graphene/Si photodetector expresses outstanding long-term stability,with negligible performance degradation even after one month in air or 1000 cycles of operation.These findings highlight a simple and novel strategy for constructing high-sensivity and ultrafast Gr/Si PDs for further optoelectronic applications.