Research On Wide Spectrum Photodetector Based On Two-dimensional Material

Two-dimensional（2D）transition metal dichalcogenides（TMDCs）have attracted extensive attention in the fields of basic science and device fabrication due to their unique physical and chemical properties.In particular,with the reduction of the number of blocks to single layers,the 2D TMDCs have changed from indirect bandgaps to direct bandgaps,which provides new ideas for single-layer TMDCs in the application of electronics and optoelectronic devices.Band gap width is an important parameter that affects the performance of semiconductor devices such as field effect transistors,photodiodes,phototransistors,and solar cells.Bandgap engineering of 2D TMDCs has become one of the emerging research priorities,as the alloying of semiconductors has shown great promise for applications such as tuning photoluminescence,absorption,and mobility.Doping of TMDCs has been shown to be an effective method to tune such electrical and optical properties.To improve the performance of optoelectronic devices,tuning of the bandgap engineering plays an important role.In this paper,using chemical vapor deposition（Chemical Vapor Deposition,CVD）,and using sodium chloride（NaCl）as a growth aid,by adjusting the mass ratio of selenium powder and sulfur powder,the monolayer molybdenum sulfur selenide(Molybdenum Sulfide Selenide,MoS_2（1-x）Se_2x)grown under different ratios was compared.MoS_2（1-x）Se_2xalloys were characterized by a series of characterizations to investigate the effect of different Se/S on the growth size of monolayer MoS_2（1-x）Se_2xalloys,control of selenium doping concentration and band gap regulation.The study found that by adjusting Se/S,six kinds of monolayer MoS_2（1-x）Se_2xalloys with different compositions were successfully obtained on Si O₂/Si（300 nm）substrate,and the adjustment of the band gap was realized.The PL peak positions of the six monolayer MoS_2（1-x）Se_2xalloys vary from 678 nm（～1.83 e V）to 813 nm（～1.53 e V）.The lateral dimension of the continuously grown large-area monolayer MoS_2（1-x）Se_2x（x=0.25）reaches 200μm.In order to study the optoelectronic properties of MoS_2（1-x）Se_2xalloys,phototransistors were fabricated using large-area-grown monolayer MoS_2（1-x）Se_2x（x=0.25）alloys.The photoelectric test results show that the monolayer MoS_2（1-x）Se_2x（x=0.25）phototransistor has a responsivity of 940 m AW^-1,a detection rate of 5.32×10¹⁰Jones,and a response time of 8 ms under 520 nm laser irradiation.These results provide a new solution for bandgap engineering of2D materials and applications in alloy devices.On this basis,in order to further expand the spectral response range of MoS_2（1-x）Se_2x（x=0.25）alloy phototransistors and improve the responsivity of the device,a PbSe colloidal quantum with a diameter of 30 mg/m L and a diameter of about 10 nm was used.Monolayer MoS_2（1-x）Se_2xalloy devices were modified by colloidal quantum dots（Colloidal Quantum Dots,CQDs）,and the fabrication of zero-dimensional and two-dimensional hybrid photodetectors was completed by spin-coating PbSe quantum dots with a thickness of 40 nm.The fabricated photodetector achieves a wide spectral response from visible to short-wave infrared（405 nm-1940 nm）,the photoresponsivity is 85 m AW^-1under 405 nm laser excitation,the detection rate is 7.64×10~5Jones,and the rise and fall times are both are 200 ms.Compared with the monolayer MoS_2（1-x）Se_2xphototransistor,the photoresponsivity is increased by about 14times and the detection rate is increased by about 3 times.Therefore,the MoS_2（1-x）Se_2xalloy photodetector decorated with PbSe quantum dots not only realizes light detection in a wider spectral range,but also improves the overall responsivity and detection rate of the device.This study will provide new ideas for future research on wide spectrum photodetectors based on two-dimensional materials.