Nanostructures And Optoelectronic Devices Of Selenium Compounds

With the development of science and technology,especially the development of semiconductor technology,people have more and more demand for high-efficiency functional materials.Of course,the demand for high-efficiency semiconductor materials is more urgent.Semiconductor nanomaterials are favored for their unique electronic and optical properties.Due to its potential applications in optics,thermology,electromagnetics and photoelectric conversion,the one-dimensional nanowire structure has attracted more and more attention.Nanowires with high aspect ratio can be used as a kind of good energy transfer material.After reasonable assembly,nanowires can be effectively used to manufacture devices based on particle transfer of electrons,photons,phonons and other particles to achieve their functional applications.Selenides are a kind of important functional materials,and selenides nanomaterials are the focus of modern materials research.Selenides nanomaterials are important semiconductor photoelectric materials,which have a series of excellent physical and chemical properties,and have broad application prospects in optoelectronic nano devices and biomedical fields.Compared with the same group of sulfur compounds and oxygen compounds nanomaterials,the research and application of selenium compounds nanomaterials in onedimensional nanostructured photodetectors are relatively lagging behind.Cadmium selenide is a class ?-? direct band gap semiconductor,with a band gap of 1.74 eV at room temperature.It has a good match with the visible light band,and has a broad application prospect in photodetectors,solar cells,light-emitting diodes,field-effect transistors,etc.In this dissertation,the synthesis of vertically aligned CdSe nanowire arrays and the application in photodetectors of a series of core-shell nanowire arrays with cadmium selenide as core are studied.The main contents of this dissertation are as follows:1?Based on the gas-liquid-solid growth mechanism,CdSe nanowire arrays were successfully prepared on fresh Muscovite substrate by chemical vapor deposition.The distribution density and position of nanowire array can be controlled by gold catalyst.The structure and morphology of nanowire array are analyzed by X-ray diffraction(XRD),transmission electron microscopy(TEM)and scanning electron microscopy(SEM).The nanowires have large area distribution and uniform shape,and grow perpendicular to the substrate along the c axis.The core-shell nanowire arrays were synthesized based on CdSe nanowire array.The growth of shell materials was realized by pulse laser deposition and magnetron sputtering.The core-shell nanowire arrays were assembled into photodetectors,and a series of photoelectric detectability tests were carried out.2?On the basis of CdSe nanowires,the CdSe-CdTe core-shell nanowire arrays UVvis-NIR photodetector was successfully fabricated.The CdTe shell was deposited on the outer layer of CdSe nanowire array by pulse laser deposition.By controlling the energy and frequency of the pulse laser,the distance between the target and the sample and the deposition time,the CdTe shell with a thickness of ~25nm was obtained.The photodetector integrated in CdSe-CdTe nanowire arrays have successfully extended the detection range from UV visible light to near-infrared light because of the unique staggered semiconductor heterojunction between CdSe and CdTe.The detection range of photodetector integrated in CdSe-CdTe nanowire arrays has been successfully extended from ultraviolet visible light to near-infrared light because of the unique staggered semiconductor heterojunction between CdSe and CdTe.Taking full advantage of piezophototronic effect of CdSe semiconductor with wurtzite structure,the photocurrent responsivity of CdSe-CdTe core-shell nanowire array UV-vis-NIR photodetector is greatly improved by simultaneously applying compression load and irradiating with UV light(385nm),visible blue light(465nm)or near-infrared light(850nm).Compared with the condition without compressed load,the absolute responsivity of devices under NIR irradiation is 3 orders of magnitude higher,and the relative responsivity variation(%)is up to 4 orders of magnitude higher.3?To improve the performance of photodetectors,in addition to improving the photocurrent responsivity,we can also enhance the device's light response speed.On the basis of CdSe-CdTe core-shell nanowire array,a layer of ZnTe with the thickness of 25 nm was recoated in the outer layer by pulse laser deposition.By scanning the profile lines of a single CdSe-CdTe-ZnTe nanowire and analyzing the EDS mapping images of each element,it is clear and intuitive to show the successful synthesis of CdSe-CdTe-ZnTe double shell nanowire.Cadmium selenide,cadmium telluride and zinc telluride form a staggered energy band structure,which is arranged in the form of a band edge cascade.Cadmium telluride in the middle layer of double shell structure limits electrons and holes in cadmium selenide and zinc telluride layers,respectively,which accelerates the separation of electron hole pairs,improves the survival time of electron hole pairs,and then successfully improves the light response speed of photodetectors.The measured response time of the device is reduced to 0.09 s.Of course,the photocurrent responsivity of the device has been greatly improved when there is light source irradiation and compression load,because of the piezoelectric photoelectron effect of the cadmium selenide.The absolute responsivity device is 9 times higher than under zero compression load,and the relative response rate variation(%)is up to 2 orders of magnitude.The absolute responsivity of the device is 9 times higher than that under the condition without of compression load,and the relative response rate variation(%)is up to 2 orders of magnitude.4?A layer of CuO thin film was deposited on the CdSe nanowire by pulse laser deposition and magnetron sputtering,respectively,to obtain the required CuO-CdSe p-n heterojunction nanowire array.The morphology of the nanowire array was studied by SEM.The surface of CuO-CdSe nanowires obtained by pulse laser deposition was uneven,and there was obvious particle deposition,which seriously affects the performance of the devices.Finally,the copper oxide shell was deposited on the surface of cadmium selenide by magnetron sputtering,and the surface of the core-shell nanowires was more uniform with better integrity.The p-n heterojunction between copper oxide and cadmium selenide accelerates the transport of photo generated carriers,and then improves the light response speed of photodetectors.The measured response time of the device is just 0.078 s.