Growth Control And Physical Properties Of Layered SnSe Low Dimensional Materials

Stannous selenide（SnSe）is a kind ofⅣmetal chalcogenide with a layered orthogonal crystal structure,a band gap value of 0.9 e V-1.3 e V and a large reserve in nature,which is P-type conductive property.The band gap of its two-dimensional material is adjustable,and the band gap value is similar to the traditional semiconductor material silicon,so it has strong light absorption in the ultraviolet,visible and near-infrared bands,which shows great potential in the application of photodetection.In this paper,single crystal SnSe nanosheets（NSs）were prepared by chemical vapor deposition（CVD）technology,and a low-dimensional photodetector was constructed based on it.In the process of characterization and performance study of materials and devices,it was observed that phonon scattering caused by inherent defects in materials would affect the photoelectric performance of devices.For improving the optoelectronic performance of the device,we tried to use CVD to prepare doped SnSe nanosheets,and SnSe nanosheets with different Bi doping concentrations were successfully prepared.At the same time,we analyzed the influence mechanism of doping on the material structure,successfully reduced the number of intrinsic defects in the material and effectively improved the optoelectronic performance of the device.The main works are as follows:（1）Firstly,SnSe nanosheets were prepared by CVD.The effects of substrate selection,growth temperature,growth time,carrier gas flow rate and other parameters on sample morphology were studied,and the most appropriate process parameters were determined.The samples were tested by basic characterization methods,and the physical properties of the samples were further analyzed.It was observed that the samples are single crystal SnSe nanoflakes with layered growth characteristics and the inherent defects were observed in the samples.The MSM structure photoelectric detection device was constructed based on SnSe nanosheets.The device showed good response to the light at 447 nm,655 nm and 980 nm,with the highest response of 1.17A/W and the highest detection rate of 1.24×10¹⁰Jones,with stable and recyclable switching response.（2）Based on the determined process parameters,SnSe nanosheets with different Bi doping concentrations were prepared by CVD,and the controllable doping of Bi was proved by various characterization methods.Further study the effect of Bi doping on the physical properties of SnSe nanosheets.It was observed that the samples were still single crystals after Bi doping,the degree of orientation was enhanced,the crystal quality was improved,and the optical absorption intensity was enhanced.With the increase of Bi doping concentration,the band gap value of SnSe nanocrystals gradually decreased,the position of band edge emission peak showed red-shift,the emission peak intensity of intrinsic defects decreased,the stoichiometric ratio of Sn and Se gradually tended to 1:1,and the number of intrinsic defects decreased.Based on Bi doped SnSe nanosheets,the MSM structure photoelectric detection device was constructed.Compared with the original device,the optical response of the device to light of different wavelengths is increased by 2-3.8 times,and the response time of the device is greatly shortened.The rise time and fall time can be shortened by 50.61%and 45.74%,respectively.（3）Further study the principle of improving the photoelectric performance of materials by Bi doping,the I-V characteristics of the two devices were tested at different temperatures.Combining the results of PL spectrum and EDS spectrum,it is found that Bi doping effectively reduce the number of inherent defects in SnSe nanosheets,resulting in lower phonon scattering intensity,it reduces the probability of photogenerated carriers suffering from phonon scattering.The photoelectric current is enhanced,and the photoelectric performance of the device is improved.