Controllable Growth Of Core-shell Nanowires And Their Photodetection Properties

Due to large specific surface area,rich surface states,high light absorption efficiency and unique electron transport characteristics,semiconductor nanowires are widely used in high-performance nano-electronic devices,photodetectors and photovoltaic devices.In order to achieve high performance of nanowire devices,core-shell nanowires emerge as the times require,and have been widely studied and concerned.Core-shell nanowires not only have the advantages of nanowires,but also have the physical and chemical characteristics of core and shell materials.In addition,the shell of core-shell nanowires can not only protect the nanowires,but also adjust the photoelectric properties of nanowires.Therefore,core-shell nanowires are regarded as a kind of "smart material",leading the development of the next generation of new high-performance optoelectronic devices.It is of great significance in both civil and military applications to realize high performance photodetectors by using core-shell nanowires.However,how to reasonably select the core-shell nanowire materials,how to control the growth of core-shell nanowires,and how to use core-shell nanowires to achieve high-performance detection devices,are the problems that need to be solved now.In order to solve the above problems,a series of researches and explorations have been carried out on the structure analysis,controllable growth and photodetection performance of core-shell nanowires.The main research contents are as follows:1.The controllable growth of GeS core-shell nanowires was realized by a simple chemical vapor deposition method.Firstly,in-situ synthesis of GeS core-shell nanowires was realized by chemical vapor deposition.Next,the effects of various growth parameters on the core-shell structure nanowires were studied.It was found that the shell thickness,length and diameter of GeS core-shell nanowires can be controlled by the growth time and catalysts thickness.After that,the core-shell structure of GeS nanowires was studied by high resolution transmission electron microscopy(HRTEM)and energy dispersive X-ray spectroscopy(EDS).It was found that the core-shell structure of GeS nanowires was composed of single crystal GeS core and amorphous sulfur rich shell.In order to further con firm the composition of the core-shell structure,the X-ray photoelectron spectroscopy(XPS)of the nanowires etched with different thickness shows that the shell composition is GeSx,and the relative content of S in the shell increases gradually from the inside to the outside.These results provide ideas for the controllable growth and structural design of other core-shell nanowires2.Using photolithography technology,GeS core-shell nanowires were fabricated into nanowire field effect transistors(NWFET).The devices show the unique negative photoresponse characteristics and high-performance detection of weak visible light Firstly,we successfully fabricated NWFET with GeS core-shell nanowire as channel material by photolithography,and studied the electrical and photoelectric properties of the device.It is found that the devices have p-type conductivity and Schottky contact mode.Secondly,through the study of its photoelectric characteristics,it is found that the device has a unique negative photoconductive effect,and achieves high responsivity(105 A·W-1)and detection rate(1012 Jones)for very weak 405 nm of 0.04 mW·cm-2 visible light.It is found that the core-shell structure inducing negative photoconductive effect is very conducive to the realization of high-performance optoelectronic devices In addition,by comparing the devices with different shell thickness,the influence of the core-shell structure on the device performance is analyzed.Finally,the physical mechanism of the negative photoconductive effect of the device is deeply studied and analyzed.It is found that the negative photoconductive effect is mainly caused by a large number of hole defects in the nanowire shell,which can capture photogenerated holes.All in all,these results suggest that core-shell nanowires have great potential in high-performance photodetectors,and provide guidance for the design and fabrication of new core-shell nanowire photodetectors in the future.