| Two-dimensional(2D)layered materials have unique optical,electrical,thermal,mechanical and other physical properties,which makes them have widely applications for high performance electronic devices,optoelectronic devices,spintronic devices,energy conversion and storage.At present,a large number of researches on 2D layered materials are mainly focused on graphene,transition metal dichalcogenides(TMDs),and black phosphorus(BP).However,some shortcomings of these materials limit their practical applications,such as the zero band gap of graphene,the lower carrier mobility of TMDs,and the air instability of BP.Recently,group Ⅳ-Ⅴ 2D layered materials with widely high carrier mobility,tunable bandgap,good stability and strong in-plane anisotropy have emerged for the promising optoelectronic applications.As a new member of the Ⅳ-Ⅴ group of two-dimensional materials,SiP has distinct advantages of environment friendly nature and dynamic stability,and the low-symmetry crystal structure makes it have intrinsic anisotropy.At the same time,theoretical calculations and experiments have proved the high carrier mobility(2034 cm2 V-1 s-1)and adjustable band gap(1.69～2.59 eV)of SiP,which is predicted to be suitable for photodetection applications.However,the research on the two-dimensional properties of SiP crystals is still blank.Therefore,the preparation and properties of 2D SiP are systematically studied in this paper.The specific work is as follows:(1)Growth of bulk SiP crystals,preparation of 2D SiP thin films and basic properties characterizationThe bulk SiP crystals were grown by the Sn flux method.By adjusting the flux proportion,cooling rate and other parameters,the bulk SiP crystal with high quality and large size was successfully obtained.Large area monolayer and few layer 2D SiP thin films were successfully prepared by mechanical exfoliation,and their structure and morphology were characterized.The high quality of 2D SiP thin films was confirmed by optical microscopy,AFM,XRD and other characterization methods.SEM and TEM showed that the 2D SiP thin films had anisotropic crystal structure.(2)Optical properties of 2D SiPThe optical properties of SiP were systematically studied by Raman specscopy,PL spectroscopy and SHG.The temperature-dependent Raman spectra exhibited that the phonon frequency in SiP is very sensitive to temperature.PL spectra showed obvious blue shift with thickness of SiP,indicating that band gap of SiP is tunable.In addition,SHG spectra exhibited obvious thickness,wavelength and power dependence,which proves the asymmetric crystal structure and nonlinear optical characteristics of SiP.(3)Optoelectronic properties of 2D SiPField effect transistors(FET)and photodetectors based on SiP flakes were fabricated to investigate its photoelectric properties.FET showed good Ohmic contact and the switching ratio reaches 103.The SiP-based photodetectors exhibited a wide-band(300-700 nm)photoresponse,ultrafast response speed(30 μs),and high stability and reproducibility.Moreover,the photodetectors still worked at a low temperature of 80 K.The results showed that the 2D SiP had great potential in the optoelectronic applications.(4)Study on anisotropy of 2D SiPThe anisotropic optoelectronic properties of 2D SiP were systematically investigated.Firstly,the polarization-dependent absorption spectra of 2D SiP were obtained,which proved the intrinsic linear dichroism of SiP.On this basis,the performance of the SiP polarization-sensitive photodetector was further studied,which showed that the SiP photodetector had excellent performance with a linear dichroic ratio of 2.3.The same orientation selectivity(along the b-axis)between absorption and photocurrent further proved the polarization photodetection ability comed from the intrinsic linear dichroism.In order to further discover the anisotropic properties of SiP crystals,we designed an angle-resolved photodetector based on the SiP flake,which exhibited good cycle stability,an anisotropy ratio of 2.9,and the performance along the crystallographic b-axis is the best. |
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