Research On The Microstructure And Detection Performance Of Novel InAsSb Nanowires And Cd₃As₂ Dirac Semi-metal Thin Films

Material engineering is the basis of the semiconductor optoelectronic devices development including size reduction,purity improvement,the introduction of appropriate defects and the update of the material system,which can all greatly improve the performance of the obtained devices.Optoelectrical detection has an unshakable position in the study of the internal physical mechanisms.Simultaneously,the disclosure of these physical mechanisms can provide new ideas for the application and design of optoelectronic devices,which could also pave the new way for the materials development.Therefore,the material structure,device structure and performance test assist one another for the optoelectronic device performance improvement,and jointly determine the direction of advanced devices.The focus of this article is divided into three parts,first:material preparation;second:device structure designing;third:device performance testing.Among them,the material preparation is carried out in molecular beam epitaxy system,which provides the possibility for atomic-level tailoring of high-quality materials.The device structures used in this article are all photodetectors,including the detectors to visible light,infrared light and terahertz.The detector waveband is the result of the combined effect of the device structure,material system,and material quality.Therefore,with given materials,the design of the device structure can effectively improve its detection efficiency in a specific waveband.Traditionally,the exploration of new material systems and the innovation of device structure have been difficult to meet the rapid development of optoelectronic devices.For the next-generation optoelectronic devices,we must pay our attention to the precise understanding and control of the material structure.This requires a more accurate microscopic understanding and controlling of materials,hence,we can design more targeted devices,maximizing the advantages of materials and device structures.As a medium,microstructure investigation can combine material growth with device applications,which can further optimize material growth and provide accurate references for device structure design.This article provides a blueprint for the use of microstructure observations to make use of materials.The main contents of this paper are divided into the following three aspects:1.InAsSb nanowire growth and its microstructure characterization:In this paper,molecular beam epitaxy is used to realize the epitaxial growth of InAsSb nanowires on Ga As substrates with the catalysis of gold nanoparticles.By adjusting the growth conditions of the nanowires including growth time,growth temperature,and beam current ratio,the morphology and microstructure of the nanowires can be tailored.In this study,InAsSb nanowires adopt a two-step growth method,which use a section of In As nanowires as a support.The two-step growth method can not only buffer the lattice mismatch between the ternary nanowires and the substrate,but also avoid the growth failure of ternary InAsSb nanowire.The microstructure characterization shows that under the same conditions,the nanowires under higher growth temperature tend to be defect-free.At low temperatures,due to the lattice mismatch to the substrate,the nanowires will tilt to one side.Through the microstructure characterization of nanowires,we found that the as-grown NWs exhibit two kinds of blemish due to the bending structure:twin defects in the tensile side and lattice distortion in the other side.2.Research on the preparation and photoelectric properties of InAsSb nanowire-based devices:As an important member of ternary III-V semiconductors,InAsSb has the advantages of high mobility,low electron effective mass,and adjustable band gap.One-dimensional nanowires obtain an ultra-high specific surface area due to the reduction in size,which triggers small size effects,quantum effects,etc.,having a significant impact on their physical properties.In this article,single nanowire-based field-effect transistors are prepared based on symmetric nanowires and asymmetric nanowires.Comparing the photoelectric performance of the two devices,it can be found that the asymmetric nanowire-based device can realize the switch between positive and negative photo-response with the modulation of gate voltage,bias voltage,and light wavelength.In contrast,the symmetrical nanowire-based devices have no similar phenomenon.Therefore,we propose that with the participation of strain engineering,asymmetric nanowire-based devices have the potential for pervasive computing.At the same time,we also use nanowire arrays to prepare array devices which is simple and low-cost coupling thousands of nanowires into one device,greatly improving the device's detecting ability to infrared light.The test indicates that the nanowire array device can exhibit a responsivity of 12.75 A/W to a LED with 945 nm wavelength at room temperature.3.The third part of this article is based on Cd₃As₂ thin-films,and studies to the detection to terahertz light with the coupling of bow-tie antennas.Cd₃As₂ is the first type of Dirac semimetal with a peculiar band structure and ultra-high electron mobility.The definite feature of the 3D Dirac-semimetal is the band disperses linearly along all the directions,and the two Dirac points protected by discrete rotation symmetry,hosting low-energy electronic excitations.Therefore,the Cd₃As₂ film shows an attractive application prospect in the field of terahertz detection.When the thickness is reduced below 50 nm,the band structure of the Cd₃As₂ film will change from a semi-metallic state to a semiconductor state dominated by the surface state.Therefore,through adjusting the thickness of the film,Cd₃As₂ can be used as a perfect medium for comparing the terahertz detection performance of semiconductor and semi-metallic materials.Finally,by introducing an asymmetric design into the device,the photoelectric process in the Cd₃As₂ film-based terahertz detector is clarified.