Study On Two-dimensional Avalanche Photodetectors Based On Four Groups Of Materials

At present,two-dimensional materials are an ideal material for preparing highperformance avalanche photodetectors because of the optical and electrical properties that break through the limit of bulk materials.two-dimensional materials have set off a new research upsurge.Compared with the impact ionization process of traditional bulk materials avalanche photodetectors,the combination of two-dimensional material layers through van der Waals force which reduces the carrier transport between layers.In this situation,the energy loss in the carrier transport process is decrease,and the impact ionization ability increase under the same bias voltage.The DRC can be suppressed in the single-photon detection.In addition,the quantum confinement effect caused by the nanoscale channel size of the two-dimensional material improves the impact ionization process and overcomes the problem of the restriction between the avalanche multiplication coefficient and the avalanche impact ionization path.The two-dimensional material also shows the ballistic avalanche effect that the bulk material does not have,which makes the avalanche impact ionization break through the limit of the minimum acceleration distance,and realizes the extremely low avalanche voltage,which makes the low voltage high-performance avalanche photodetector possible.The research of two-dimensional material avalanche detector mostly focuses on the avalanche multiplication mechanism,but the research of the integrated device structure is not enough.Designing a device structure that meets both the avalanche effect occurrence conditions and the photodetection requirements is a key scientific problem to be solved urgently.In order to solve this problem,this paper firstly studies the two-dimensional material avalanche field effect transistor based on silicon oxide on four kinds of substrates.On the one hand,the two-dimensional material avalanche device fabricated on silicon oxide lays the foundation for the integrated research,on the other hand,silicon oxide as a gate medium adds a device modulation dimension to break through the application bottleneck of traditional avalanche detectors.In this paper,a device structure for reducing avalanche voltage through graphene is proposed,and the influence of contact resistance on avalanche effect is studied.In addition,for ambipolar materials,the competition mechanism between ambipolar transport and avalanche multiplication effect is studied,and the modes of avalanche multiplication effect and ambipolar transport are selected through contact electrodes.A method of transforming ambipolar transport into avalanche multiplication by local gate voltage modulation is proposed.Next,a device performance improvement scheme based on out-of-plane PN junction structure is proposed for avalanche multiplier devices.The avalanche breakdown voltage is reduced and the detection wavelength is extended,which provides a feasible design scheme for the high-performance two-dimensional material avalanche detector.Finally,based on the study of two-dimensional/three-dimensional material hetero-integrated avalanche detector,the evolution law of hetero-integrated avalanche multiplication is studied through experiment and simulation.A low voltage avalanche multiplication scheme with intercalation structure is proposed.The specific research contents are as follows:1.The internal physical mechanism of its doping type change by changing the electrode at WS2 field effect transistor was stuided.It found that the hole impact ionization is realized when gold is the electrode,and the electron impact ionization is realized when graphene is the electrode.On this basis,the physical mechanism of gate voltage modulated avalanche breakdown voltage is studied,and the evolution of scattering and impact ionization in two-dimensional materials is analyzed.In addition,graphene is used as the electrode to reduce the avalanche breakdown voltage of the device.Because of the graphene electrode can replace the gold electrode to reduce the height of Schottky barrier,thus improving the influence of contact resistance on the electric field distribution which is studied by simulation.At a lower Schottky barrier,the internal electric field strength of the device can be enhanced.In this study,under 532 nm illumination,WS2 field-effect transistor has ultra-low dark current(10-12A),high response rate(74 A/W)and ultra-high detectivity(1.45 × 1016 Jones).This research results of this paper provide a new design idea for the design of two-dimensional material avalanche photodetector.2.In view of the unique characteristics of two-dimensional materials,this paper studies the internal physical mechanism of ambipolar transport and avalanche multiplication effect caused by ambipolar WSe2 materials under high voltage.We explore the internal competition mechanism and find the contact electrode barrier height adjustment on these two effects.Such as the avalanche multiplication effect is realized through the contact of gold electrode,while the ambipolar transport is realized through the contact of graphene.Moreover,the correlation between avalanche voltage and avalanche region in WSe2 field effect transistor is analyzed by photocurrent mapping diagram, and a research method for avalanche device design is proposed.On this basis,the physical evolution process of ambipolar transport transforms into avalanche multiplication effect under external gate voltage is explored.We proposed a device structure with local gate voltage to modulate the avalanche effect and ambipolar transport.The structure changes the position of Fermi energy level in the inversion region through local gate voltage,and suppresses the accumulation of minority carriers caused by large bias voltage,thus modulating the transition from bipolar transport to avalanche multiplication.This research opens up a new path for the practical application of new avalanche photodetector.3.Based on WSe2 avalanche field-effect transistor,a low-power structure is proposed to realize avalanche breakdown voltage through out-of-plane PN junction.The intrinsic mechanism is mainly related to the redistribution of electric field in WSe2 channel after the formation of out-of-plane PN junction.In this study,the avalanche breakdown voltage can be reduced from-31 V to-8.5 V.The intrinsic mechanism of reducing avalanche breakdown voltage and the mathematical model of physical parameters and voltage reduction are also studied.The low voltage avalanche photoelectric detection is realized,with ultra-low dark current(10-11A),high response rate(165A/W)and ultra-high detection rate(3.53)under 532 nm illumination × 1012 Jones.By replacing Ge material,the detection spectrum of avalanche photodetector is also broadened.This result shows that the replacement material can not only modulate the breakdown voltage but also broaden the detection spectrum.The research results provide a new design idea for low-voltage avalanche devices.4.Based on the research of two-dimensional/three-dimensional material heterointegrated devices,the evolution of tunneling effect and avalanche effect caused by different energy band structures is studied,and the design scheme of hetero-integrated low-voltage avalanche multiplier devices is explored.The generation process of avalanche multiplication effect in heterostructure integrated devices and gate voltage modulation mode were explored by preparing WSe2-Ge(n)and WS2-Ge(p).The 1550 nm infrared light detection with high performance is realized,and the heterointegrated device has high response rate of 10A/W and ultra-high specific detection rate of 3×1012 Jones.On this basis,the evolution law of energy band pair tunneling effect and avalanche effect is studied through the heterogeneous integration of BP with N-type Ge and P-type Ge materials.The design scheme of the two-dimensional/threedimensional material hetero-integrated avalanche photodetector is proposed.The BP material is used as the insertion layer,so that the electric field is concentrated in the region and the low-voltage avalanche multiplication is finally achieved.The avalanche breakdown of about 2V is achieved in the WS2-BP-Ge(p)device.The evolution process of tunneling effect and avalanche multiplier effect in the intercalation structure is analyzed by simulation.The research results provide a new design idea for lowvoltage avalanche devices.