| Before the discovery of graphene in 2004,humans were able to fabricate and utilize three-dinensional,one-dimensional and zero-dimensional materials to construct devices with various functions.However,the preparation of two-dimensional materials was never able to make a breakthrough.It was generally believed that the two-dimensional material could not be stably existed under normal temperature and pressure due to the instability of its crystal lattice.Therefore,few research groups have targeted two-dimensional material preparation.The discovery of graphene is just like the last piece of the puzzle,opening the door to research on physics,materials and devices under the two-dimensional framework.The appearance of graphene indicates that it is possible to construct devices at the level of a single atomic layer or a polyatomic layer,and this represents the direction of human scientific research.As a result,graphene has set off a wave of research around the world,and many new two-dimensional semiconductors has been discovered.Graphene and two-dimensional semiconductors are an important part of the two-dimensional material family.Since Andre Geim and Konstantin Novoselov,have won the Nobel Prize for nine years,and graphene has been discovered for fifteen years,the research on the physical aspects of graphene and two-dimensional semiconductors is endless.There is an urgent need to explore its possible applications in actual production.So far,it is internationally recognized that graphene and two-dimensional semiconductors have unique advantages in the field of optoelectronic devices.Taking graphene as an example,it has high transparency,good electrical conductivity and high carrier mobility,and has broad application prospects in transparent conductive layers or high-speed photodetection.At the same time,graphene and two-dimensional semiconductor can be directly combined with traditional three-dimensional semiconductor materials to form a heterojunction with a junction region on the surface,thereby greatly expanding the application range of the device.Different two-dimensional semiconductors are also different in properties.A plurality of two-dimensional semiconductors can be used to construct optoelectronic devices,the two-dimensional semiconductors can be complemented to improve the performance of the device.The two-dimensional/three-dimensional heterostructure formed between graphene and two-dimensional semiconductor and three-dimensional semiconductor has unique physical connotation and application value.Taking graphene/GaAs gallium heterojunction as an example,from the perspective of carrier dynamics,graphene itself also has ultra-wideband light absorption and multi-exciton effect,which can participate in the process of carrier generation.The photo-generated carriers in the heterojunction can be transferred between graphene and gallium arsenide in the femtosecond scale,which can improve the collection efficiency of carriers.From the perspective of the spatial distribution of the carrier,the depletion layer and the light absorbing layer overlap in space,which reduces the loss of carriers during the drift and diffusion motion,and helps the carrier to be efficiently generated.Separation.These characteristics of two-dimensional/three-dimensional heterostructures break the physical basis of breaking the performance limitations of traditional optoelectronic devices.The performance optimization methods and effects of 2D/3D heterostructures are also quite different from those of traditional PN structures.Taking the local surface plasmon resonance enhancement method as an example,the hot spot energy generated by surface plasmon resonance is a near-field distribution,which rapidly decays with increasing distance,while the conventional PN junction region is located at a depth of several hundred nanometers or even several micrometers below the surface of the device.It is difficult to enhance plasmon resonance.However,since the two-dimensional/three-dimensional heterostructure has a structure on the surface,the enhanced electromagnetic field generated by the surface plasmon resonance spatially overlaps the depletion layer and the light absorbing layer,thereby greatly improving the performance of the device.At the same time,graphene and two-dimensional semiconductors in two-dimensional/three-dimensional heterostructures can be enhanced by means such as surface energy band adjustment,chemical doping and anti-reflection layer.Since graphene and two-dimensional conducting halves are applied to optoelectronic devices,problems such as low absorbance and inability to turn off the device exist,and in various fields of optoelectronic devices,there is an urgent need to improve the performance of existing devices.How to solve these problems?The hetero structure of graphene and two-dimensional semiconductors can be an effective solution.This thesis focuses on the practical application of heterostructures of graphene and two-dimensional semiconductors in the field of optoelectronic devices.Several different types of optoelectronic devices based on graphene and two-dimensional semiconductors are studied,involving graphene and two-dimensional hexagonal nitridation.Boron,two-dimensional molybdenum disulfide,and introduced methods to improve device performance through interface band adjustment,surface doping,local surface plasmon resonance enhancement,etc.,explored the physical mechanism behind performance improvement,further prompted graphite The physical content of the heterostructure of olefins and two-dimensional semiconductors,the specific content has the following parts:1)A graphene/hexagonal boron nitride/zinc oxide heterogeneous photodetector was proposed,and the role of boron nitride material in the heterojunction was investigated.Hexagonal boron nitride could increase the electron barrier of graphene/zinc oxide devices,further increase the responsiveness of the device at 365 nm to 1350 A W-1,and improve the on-off ratio of the device to 103.2)A graphene/gallium nitride light-emitting diode was manufacture by wet transfer technique,which could emit light in both the forward and reverse directions and have different wavelengths.The introduction of silver nanoparticles at the interface could enhance the luminous intensity.By fitting the spectrum,we believed that the surface plasmon resonance effect of silver nanoparticles could be coupled with excitons in the surrounding environment,increasing the proportion of the radiation recombination of the device in the carrier recombination process,thereby improving the luminescence of the diode.3)The gold nanoparticle-enhanced Graphene/GaAs solar cells were studied,and a conversion efficiency of 16.2%was achieved.By spin-coating a layer of chemically synthesized gold nanoparticles on the surface of a graphene/GaAs solar cell,the localized surface plasmon resonance effect of the nanoparticles could be used to constraint the incident light on the deplete layer of graphene/gallium arsenide,which accelerated the separation of photogenerated carriers,and increased the short-circuit current density of solar cells from 19.1 mA cm-2 to 24.9 mA cm-2.Combineing with doping and anti-reflection means,solar cell conversion efficiency could increase to 16.2%.The effects of the diameter and distribution density of gold nanoparticles on the conversion efficiency of the solar cell were investigated.4)The photoluminescence enhancement and photodetection enhancement of molybdenum disulfide in nano-gap structure were studied.Under suitable electromagnetic excitation,a gap-mode plasmon was produced in the metal nanogap,accompanied by an electromagnetic field enhancement effect.At this time,a single layer of molybdenum disulfide was inserted into the metal nano-gap,and 110 times of photo luminescence enhancement and 882%of photocurrent enhancement were obtained,which reached 287.5 A W-1. |
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