Graphene And Molybdenum Disulfide Based Infrared Photodetectors

With the development of modern information technologies,there are more requirements to put forward in optoelectronic applications,especially in photodetectors.The traditional semiconductor photodetectors based on thin films of silicon or III-V family are hard to meet the increasing practical application requirements due to the limitations of complex manufacturing process,high cost,and low operating temperature.With the discovery of graphene and other two-dimensional?2D?materials,they are widely studied in photodetectors application due to their abundant species,excellent mechanical flexibility,unique electrical and optical properties,easy processing and integration.These merits are expected to address the shortcomings of traditional semiconductor photodetectors.However,the design and fabrication of photodetectors based on 2D materials still face some scientific or technical challenges.First,although the two-dimensional materials have a wide light response range,the absolute values of their absorption are still too low to detect the infrared lights.The present researches show that the surface plasmons and heterostructures can effectively enhance the interactions between incident lights and two-dimensional materials.However,the main challenge of these photodetectors is the patterned materials using the complicated process may damage their inherent electrical or optical characteristics.In this dissertation,we focus on the fabrication and enhancement of the infrared detection performance of the photodetectors based on graphene and ultra-thin molybdenum disulfide.We systematically describe the materials preparation,device design,micro-nano fabrication,and device performance.We further investigate the internal relations among the intrinsic bandgap,carrier transport behavior,interface electric field distribution,device detection modulation,and related physical mechanisms.The details are listed as follow:Firstly,the 2D materials preparation and photodetector fabrication are investigated.High-quality single-layer graphene using wet transfer onto different substrates was obtained,which provides a general method to transfer CVD growth 2D materials without ripples and damage-free.Employing a special transfer platform with micro-distance control optical microscope,2D materials can be easily obtained and stacked in various ways using dry transfer technique,laying the foundation for the heterostructure stack and device fabrication.Moreover,using direct writing lithography and reactive ion etching technologies,we can fabricate a variety of electronic films and 2D materials with desired patterns.Combined with the above-mentioned 2D material preparation and accurate transfer technologies,we built a platform for systematic processing of 2D material-based optoelectronic devices.Secondly,the tunable infrared photodetector with monolayer graphene/periodic ferroelectric striped domains hybrid structure is studied.We propose a novel periodic ferroelectric striped domain array to effectively excite and modulate the graphene surface plasmons.This approach does not need of the patterned graphene or the introduction of a nano-metal array.When the periodic ferroelectric domain array matches the incident light wavelength,the excited graphene surface plasmons wave resonates with the incident light,which greatly enhances the optical response to the wavelength.Using the finite element method to simulate our designed device,the optical absorption reaches up to 38%in graphene/periodical ferroelectric domain structure,while the absorption in graphene/single ferroelectric domain is less than 1.5%.The theoretical detection rate of the device is as high as 10¹³ Jones at room temperature,which is comparable to the order of the present commercial low-temperature infrared photodetectors.Meanwhile,due to reversible ferroelectric domains,we can simply rewrite the graphene carrier patterns to modulate the position of the selective absorption peak in the range of 5²0?m.Further,the experimental results confirm our simulation for the tunable infrared photodetection using graphene/periodical ferroelectric domain structure.When the graphene carrier-density patterned at nanoscale?1?m to 200 nm?by periodically striped domains in BiFeO₃ thin film,the position of graphene selective response can be tuned from 8.5?m to 7.2?m without gate voltage,or patterned graphene.As well,the photoresponsivity and detectivity of the device can reach³0 mA W^-1 and 1.67×10⁹ Jones respectively,under⁸.5?m illumination,which is equivalent to the performance of the existing graphene plasmonic photodetectors.Thirdly,the enhanced photodetection of molybdenum disulfide by Au surface plasmons in the near-infrared region is studied.Firstly,the Au nanoparticles with uniform distribution and controllable size are prepared by template-free magnetron sputtering on ultra-thin molybdenum disulfide.When the surface plasmons excited by the introduced Au nanoparticles resonate with the incident light,the local electric field at the interface between the gold particles and molybdenum disulfide is greatly enhanced,and the photoresponse of the device is effectively improved in the band of 700¹600 nm.Under980 nm illumination,the responsivity of the device can reach 64 mA W^-1.Fourthly,the broadband photodetector with an ultra-fast response based on vertical stage-liked molybdenum disulfide/silicon heterostructure is studied.By using rapid annealing technology,the ultra-thin molybdenum disulfide transferred on the heavily doped p-type silicon is patterned as a vertical stage.The heterojunction of this special structure is equivalent to that of molybdenum disulfide with different thicknesses and sizes stacked on a silicon wafer for many times,and the morphology and thickness can be simply controlled by the rapid annealing time.When it used as photodetectors,it has a strong light response in the range of 405-980 nm,which effectively broadens the light response range,compared with the bare molybdenum disulfide.Under 808 nm illumination,the photoresponsivity of the device can reach 746 mA W^-1,which is higher than that of MoS₂-Si lateral heterojunction.Moreover,the response time of the device with this structure is ultra-fast,and the rise time and fall time of the response is¹78?s and¹98?s,respectively,which is superior to the other type detectors based on MoS₂.