| Recently,2D layered materials have attracted increasing attention and enthusiasm because of their exceptional electronic,optical and mechanical properties,such as graphene,transition metal dichalcogenides(TMDs)black phosphorus,etc.Orthorhombic SiP(o-SiP)is a novel 2D layered crystal.The growth and properties of novel orthorhombic SiP(o-SiP)are not only important to extend our current knowledge of 2D materials,but also may significant impact on future electronic technologies.In this paper,large-sized bulk o-SiP single crystals have been successfully grown by seeded flux method.The basic physical properties and in-plane anisotropy were researched in detail.Main contents and conclusions in this dissertation are as follows:Ⅰ.Controllable flux growth and optic-electric properties of bulk o-SiP crystals.Large-sized bulk o-SiP single crystals have been grown successfully by flux method for the first time.The size and morphology of o-SiP crystals can be controlled by tuning the cooling rate.The energy band gap of bulk o-SiP is determined to be 1.71 eV and its mobility is 2.034 ×103 cm2·V-1·s-1 which is ten-fold of MoS2.DSC/TGA characterization indicates that o-SiP is thermodynamically stable up to 1045 ℃.Fast laser responses indicate that o-SiP is a sensitive photodetector.Our experimental results indicated that o-SiP might be a promising 2D material for electronics and optoelectronics applications.Ⅱ.Mechanical exfoliation few-layer o-SiP nanosheets with tunable band gap.Highly quality o-SiP nanosheets with large area were obtained by mechanical exfoliation technique with self-made o-SiP crystals.Morphology and microstructure of nanosheets were investigated by SEM and TEM.DFT calculations indicates that o-SiP,an indirect band gap material in bulk form,becomes a direct band gap semiconductor when thinned to a monolayer.Ⅲ.Rearsch on in-plane anisotropy of o-SiP.We identify all the experimental Raman modes of o-SiP based on DFT calculation for the first time.Meanwhile,the polarized Raman spectra distinctly reveal the anisotropy of Raman intensity.As a simple and nondestructive method for identifying crystalline orientation,polarized Raman spectrum is of great benefit for the research on anisotropy of o-SiP.O-SiP based photodetectors show high photosensitivity,allowing them to act as high-quality photosensitive switches.More importantly,the results indicate high in-plane anisotropic photoresponse along a-and b-axis.A notably anisotropic on/off switching ratio indicates that o-SiP is a promising 2D material candidate for future optoelectronic applications,especially when the anisotropy is desirable.In addition,our results highlight the structural and optoelectronic anisotropy of o-SiP.It will provide useful guidelines for exploration of applications in electronic,optoelectronic devices based on IV-V group 2D layered semiconductors.Ⅳ.Growth of CdSiP2 crystal.Ternary silicon diphosphide compound CdSiP2(CSP)crystal is an important mid-infrared non-linear optical crystal due to large nonlinear coefficient and high thermal conductivity.In addition,it can be pumped by commercially available laser such as Nd:YAG operating at wavelength around 1 μm without TPA.However,it is difficult to grow large-sized,crack-free crystals directly from melt mainly due to the high melting point(1133 ℃)and extremely high dissociation pressures at their melting temperature(22 atm at 1133 ℃).This severely limits volume production and applications.Using experience growing o-SiP crystal,CSP crystals were grown by flux method to solve the explosion of quartz tube.Meanwhile,o-SiP crystals were grown by vertical-Bridgman method and try to help the growth of CSP crystal in the future. |
