Research On Photoelectric Properties Of Low-Dimensional Ternary Chalcogenides

Low-dimensional materials include two-dimensional(2D),one-dimensional(1D),and zero-dimensional quantum dot materials(0D),and their rich physical properties due to quantum confinement effect have attracted a great deal of attention from researchers,which can be applied to photodetectors,sensors,transistors,thermoelectricity,superconductivity,etc.So far,the vast majority of research into lowdimensional materials is based on single-element and dual-element systems.The ternary system,however,is best represented by ternary chalcogenides,which introduce degrees of freedom in elements compared with binary chalcogenides,allowing for a more diverse crystal structure.The opening of the lattice is beneficial to element doping,phase control,and property modulation.In addition,the characteristics of high mobility,magnetism,and topological state transition in ternary chalcogenides provide a new platform for the study of anomalous Hall effect,magnetic transition,superconductivity,nontrivial topological phase,and high-performance detectors.Meanwhile,ternary chalcogenides promote the construction of novel optoelectronic devices and have great application potential in future nanostructured devices.This thesis focuses on the high-quality synthesis,physical properties,and broadband photodetection of ternary chalcogenides.At first,the low-dimensional materials were obtained by mechanical exfoliation,and their optical properties as well as carrier transport properties were systematically studied.Based on the advantages of the special band structure and physical properties,then combined with antenna simulation technology and device structure design,the high-performance broadband and terahertz(THz)photodetectors have been successfully constructed.Finally,the response mechanisms of the photodetectors are explored deeply.The main research contents are as follows:1.High-performance ultraviolet and near-infrared wide-spectrum detectors were developed.Based on ternary narrow bandgap chalcogenides,highly sensitive broadband detection is realized by photoconductive effect and multi-channel transition mechanism.(1)High-quality Ta2NiSe5 bulks were synthesized by the chemical vapor transport(CVT)method,and the Fourier transfer infrared spectrometer(FTIR)measurement was conducted to study the optical absorption property of the Ta2NiSe5 nanoflake(～0.33 eV).A high-performance broadband Ta2NiSe5 photodetector with a spectrum ranging from 405 nm to 4300 nm based on the photoconductive effect is demonstrated.The constructed Ta2NiSe5 photodetector shows a highest responsivity of～198.1 A·W-1 at 1350 nm.And the response time is～27.4 μs.(2)The noble 1D GePdS3 nanowires were synthesized via a CVT method.The phonon vibration modes were determined by the Polarized Raman spectroscopy and density functional theory(DFT)calculations.The constructed GePdS3 photodetector proves its excellent performance over a broadband spectral region ranging from ultraviolet to near-infrared,exhibiting a superb responsivity up to～219 A·W-1 and a remarkable detectivity of～2.7×1010 Jones under 254 nm illumination.2.A wide-spectrum THz detector driven by magnetic topological phase was developed.The magnetic element Co was intercalated with binary NbS2 to obtain CoNb3S6.The Co intercalation introduced a new dispersion band near the Fermi level,determined by angle-resolved photoemission spectroscopy(ARPES).Kramers-Weyl(KW)Weyl point and non-centrosymmetric structure were also brought by the Co intercalation.Then,a broadband THz detector was prepared on high-resistance intrinsic Si substrate with the finite different time domain(FDTD)antenna simulation technology.Based on the broken symmetry and topological transformation,the responsivity of the device is～0.31 A·W-1 and the noise equivalent power is～10.5 pW·Hz-1/2 at zero bias.In addition,the performance of the device has no obvious attenuation under high-speed modulation frequency.At the same time,the device can realize high-resolution nondestructive imaging.3.Quasi-1D ternary topological chalcogenides were developed,and the results show strong topological surface states.Furthermore,the nontrivial topological band structure is utilized to realize high-performance THz detection.(1)High-quality TaNiTes crystals were grown by the flux method.The Dirac cone is directly observed in the profile by the ARPES.Then hall devices were constructed by TaNiTe5 nanosheets.The MR reaches 500%at 8 T,the carrier concentration and mobility of TaNiTe5 nanosheets are～6.25×1021 cm-3 and～23800 cm2V-1s-1 at 15 K,respectively.Then,the THz devices were constructed by TaNiTe5 nanosheets,and high-performance THz detection is realized by using Dirac surface states.The responsivity of the device is～33.2 mA·W-1 and the noise equivalent power is～645 pW·Hz-1/2 at 100 mV.(2)Highquality quasi-1D Ta2PdSe6 crystals were synthesized by the CVT method,which was predicted to be a topological insulator.The strong topological surface state and linear dispersion relationship were determined by ARPES.Then hall devices were constructed by Ta2PdSe6 nanosheets.The results show that the MR is～447.5%at 12 T at 1.5 K.Meanwhile,The Hall resistance shows nonlinear characteristics,after dualband model fitting,the obtained hole and electron mobility of Ta2PdSe6 nanosheets are～12500 cm2V-1s-1 and～400 cm2V-1s-1,respectively.Ta2PdSe6,a topological insulator with quasi-1D structure,is expected to be utilized in highly sensitive THz detectors and to explore the novel mechanisms brought by strong topological surface states.