Research On Two-dimensional Material Photodetector Based On Graphene/MoSe₂

As a fundamental device for sensing information,photodetectors have a wide range of applications in military,civil and scientific research.Two-dimensional transition metal sulphides（TMDs）have excellent properties for the preparation of high-performance photodetectors,such as layer-dependent energy band structure,broad absorption spectra and high carrier mobility.However,noble metals as electrode materials have disadvantages such as brittleness and low light transmission,and there is a fermi energy level pinning effect between TMDs and noble metal electrodes,making the carrier transport modulation extremely difficult.In this thesis,a typical TMDs material,molybdenum diselenide（MoSe₂）,is used as the channel material and a 2D material,graphene（Gr）,is used as the electrode material to construct a MoSe₂/Gr based all 2D material photodetector and to investigate its optoelectronic properties.The main elements are as follows.（1）High quality graphene and MoSe₂layer less samples were prepared by mechanical exfoliation method.The sample morphology was observed by optical microscopy and the number of layers was judged by calculating the optical contrast,followed by Raman and photoluminescence spectroscopy of the samples,and the number of layers was verified by the peak information appearing in the sample spectra.（2）The photodetector was constructed on the SiO₂/Si substrate by dry transfer technology.When no light was on,the output curve of the device was basically straight in the range of-1 V to 1 V,indicating ohmic contact between the channel and the electrode.The performance of the photodetector was investigated and the following conclusions were drawn:At constant incident optical power density and incident wavelength,the applied bias voltage increases from 0.1 V to 1 V,and the net photocurrent,photoresponsivity and specific detection rate of the device increase;at constant incident optical power density,as the bias voltage increases,the incident wavelength increases from 515 nm to637 nm and 670 nm,and the net photocurrent,photoresponsivity and specific detection rate of the device decrease with increasing wavelength.With constant bias and incident wavelength,the incident optical power density increased from 0.52 m W/cm²to 2.08m W/cm²,and the net photocurrent of the device increased,but the optical responsiveness and specific detectivity decreased;with constant bias,the incident optical power density increased from 0.52 m W/cm²to 2.08 m W/cm²,and the wavelength increased from 515 nm to 637 nm and 670 nm in sequence,the net photocurrent,photoresponsivity and specific detectivity of the device decreased with increasing wavelength.During testing,the device performance was measured to be at its best when the optical responsiveness and specific detectivity were 639.5 m A/W and 5.55?10⁸Jones respectively.（3）A layer of h-BN was transferred between the SiO₂layer and the MoSe₂channel to improve the contact between the channel and the substrate,and the optoelectronic performance of the optimised device was tested using a laser with a wavelength of 637nm as the test light source.When compared with the initial device,the results show a significant improvement in the performance of the optimised device under the same conditions.For example,at a bias voltage of 1 V and an incident light intensity of 2.08m W/cm²,the optical responsivity and specific detection rate of the optimised device correspond to values of 2.83 A/W and 7.24×10⁸Jones,respectively,which are 7 times（404 m A/W）and 2 times（3.51×10⁸Jones）of optimised device.The detection performance of the same light source is more stable,and tests on the optical responsivity of the same light source show that when the light intensity is increased from 0.52 m W/cm²to 2.08 m W/cm²,the optical responsivity before optimisation decreases by more than 20%,while after optimisation the optical responsivity only decreases by about 4%.