Research On Fabrication And Characterizations Of MoS₂/Ⅲ-Ⅴ Semiconductor Microtube Heterojunction Photodetector

Photodetectors have been widely used in many fields,such as optical communications,optical sensing,imaging,aerospace and so on.How to realize omnidirectional detection has gradually become a research hotspot with the development of autonomous driving,the current method is to assemble planar photodetectors into a 3D detection equipment,which is difficult for further integration because of its large size.Our laboratory and several other domestic and foreign groups are committed to fabricating 3D microtube photodetectors with the help of self-rolled-up technology to realize omnidirectional detection.The self-rolling of a planar structure requires a thinner thickness,which limits the photoresponsivity of photodetector and performance improvement.2D materials can form high-quality planar heterojunction with semiconductors,which can be transform into microtubular heterojunction and microtubule heterojunction photodetector by self-rolling,this process may cause some 2D materials to exhibit anisotropic light absorption behaviors after being stressed,thus enabling the photodetector to detect linearly-polarized light.However,at present,there is no report on the design and fabrication of microtube heterojunction photodetector for reference,so it is worth further study.This thesis focuses on the fabrication and characterizations of microtube heterojunction photodetector.Molybdenum disulfide(MoS2)is used to form a van der Waals heterojunction with In0.23Ga0.77As/GaAs,the compatibility problem between device design,preparation and self-rolling process of semiconductor has been solved.A self-powered microtube heterojunction photodetector with omnidirectional detection capability and linearly-polarized light detection capability is obtained,the main work and results of the thesis are as follows:1.Solve the electrode preparation problem of three-dimensional microtubule photodetector.The device structure and process flow of a MoS2/Ⅲ-Ⅴ semiconductor microtube heterojunction photodetector has been designed in this thesis,which is compatible with self-rolling process of semiconductor.The scheme of "2+1" type co-planar electrodes that our group innovatively proposed before has been used,two outer-wall electrodes are symmetrically pressed against MoS2,limb onto the inner-wall electrode which is located in the middle of the outer-wall electrodes after the planar heterojunction rolled up into a microtube heterojunction by controlling the etching process,thus the inner-wall electrode can form good electrical contact with In0.23Ga0.77As like the contact between two outer-wall electrodes and the MoS2.SiO2 was deposited at the bottom of the outer-wall electrode to insulate the electrodes and was protected by photoresist from being etched by HF solution.We use the probe station to record the current between the inner-wall electrode and an outer-wall electrode when the bias voltage increases from-3V to 3V,significant rectification effect can be observed(rectification ratio reached 1.16×102,reach the average level).2.The self-driven omnidirectional detection performance of the photodetector has been verified.A simple apparatus using an iron stand and a flexible bracket that can change the angle of the laser(520nm green light)has been built.We change the incident light angle from 0 ° to±90 °(We define that the incident light angle is 0° when the laser is vertically irradiated onto the detector and the angle is 90° when it is parallelly irradiated onto the device)with the interval of±10° and record the photocurrent of the photodetector under a bias voltage of 0 V.The results show that the microtube heterojunction photodetector we fabricated always has photoresponse when the incident light angle from 0° to ±70°and the response is greater than 0.56mA/W(the responsivity reaches the maximum when the incident light anglle is 0 °,which is 2.83mA/W,reach a usable level),demonstrating that the photodetector has self-powered omnidirectional detection capability.3.The self-driving polarization detection function of photodetector has been verified.Another simple polarization capability testing apparatus was built with the help of an iron bracket,a 3D adjustable bracket and a polarizer.We illuminate a 532nm laser on a polarizer to generate linearly-polarized light,and then rotate the polarizer in a plane at 0V bias to test the maximum and minimum photocurrent,the dichroic value of the microtube heterojunction photodetector can be obtained by dividing them(1.85 for vertical incidence and 1.81 for incline incidence,reach the average level).It has been demonstrated that the microtube heterojunction photodetector we fabricated achieves self-powered omnidirectional detection of linearly-polarized light,such ability comes from the anisotropic light absorption behaviors of MoS2 after being rolled up.which is consistent with the shift and splitting of Raman characteristic peaks of MoS2.