Optimization of Photodetector Performance in MoTe2/MoS2 Heterojunctions Based on Surface Engineering Regulation
This study aims to improve the performance of MoTe2/MoS2 heterostructure-based optoelectronic devices by utilizing surface engineering techniques,specifically organic molecule doping and annealing.The focus is on optimizing the electronic properties of these heterostructures to enhance their optoelectronic performance,making them more suitable for applications in various photodetectors and other optoelectronic devices.MoTe2 and MoS2 thin layers were prepared using mechanical exfoliation,ensuring high-quality samples.The MoTe2/MoS2 heterostructures were then fabricated using a dry transfer method.To improve the properties of the heterostructures,the samples were doped with organic molecules,including 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane(F4-TCNQ)and rhodamine 6 G(R6G).After doping,the samples underwent an annealing process to further optimize their electronic properties.These devices were characterized using Keithley instruments for current-voltage measurements and photocurrent testing,while structural and morphological observations were carried out with a Leica DM2700 optical microscope.The performance of the devices was analyzed under different bias and illumination conditions to assess the effects of surface engineering on their optoelectronic properties.The experimental results revealed that the surface-engineered MoTe2/MoS2 heterostructures exhibited significant improvements in their optoelectronic performance.Under a-2 V bias and 637 nm illumination,the photocurrent increased substantially from 8.23×10-8 A at zero bias to 7.12×10-7 A,while the photoresponse time decreased from 4.12×10-8 s to 7.49×10-9 s.These improvements correspond to a significant increase in sensitivity,conversion efficiency,and response speed,indicating that surface engineering,including organic molecule doping,plays a critical role in enhancing the performance of MoTe2/MoS2 heterostructure-based optoelectronic devices.Among the doping agents tested,F4-TCNQ was found to be particularly effective,as it significantly modified the electronic structure of MoS2,contributing to the formation of a potential barrier at the MoTe2/MoS2 interface.This barrier,resulting from the difference in Fermi levels between MoTe2 and MoS2,induced band bending at the heterojunction interface,which played a crucial role in improving carrier transport and reducing recombination losses of charge carriers,leading to better device performance.The photoresponse characteristics of the device also exhibited significant improvement after doping.Due to the material thickness and the risk of device breakdown under prolonged high-power illumination,the experiments were conducted within a power range of 57.67 µW to 207.1 µW.Compared to the intrinsic MoTe2/MoS2 heterostructure's photoresponse time under zero bias,the doped MoTe2/MoS2 device with a coplanar electrode structure demonstrated a reduction in photoresponse time from 2.27×10-4 s to 1.42×10-4 s under illumination at λ=637 nm with an incident power of 18.94 μW.Additionally,a power-dependent response was observed,indicating the existence of an optimal power level at which the photodetector achieved peak response speed,likely due to saturation effects.When the incident power exceeded a certain threshold,the photodetector entered a saturation state,although the exact threshold power range could only be approximately estimated due to the precision limitations of the measurement equipment.These findings emphasize the importance of considering power factors in the design of optoelectronic devices to balance photo response time and rectification ratio.On the other hand,R6G doping had a relatively smaller effect on improving performance compared to F4-TCNQ,likely due to its weaker electron-withdrawing properties.In addition,to study the effect of surface treatment on the MoTe2/MoS2 heterostructure photodetector,annealing treatment was applied to the heterostructure devices.This helped reduce defect density and improve the crystallinity of the MoTe2 and MoS2 layers,further enhance carrier mobility and overall device performance.Although no significant adsorption of organic molecules on the lower MoTe2 layer was observed,the effect of F4-TCNQ doping was still evident,likely because it can alter the electronic properties of the entire heterostructure.The above experiments have demonstrated that surface engineering through organic molecule doping and annealing treatment is an effective method for enhancing the performance of MoTe2/MoS2 heterostructure optoelectronic devices.Among the organic molecules tested,F4-TCNQ showed the most pronounced effects,resulting in significant improvements in carrier transport,photocurrent,and response time.These findings highlight the potential of surface engineering in optimizing the functionality of optoelectronic devices made from 2D materials and provide valuable insights for the design and fabrication of high-performance optoelectronic systems.
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