The Synthesis And Electrical Properties Of CdS Based Nanowires

Because of unique physical and chemical properties,one dimensional semiconductor nano materials have attracted much attention,such as nanorods,nanowires and nanotubes.II-VI semiconductor materials have attracted much attention because they have excellent physical properties such as the direct transition,wide absorption and emission wavelength range.Their band gap can also be adjusted in a wide range.Among the II-VI semiconductor materials,CdS a is very good n-type photoelectric material.It can absorb a wide range wavelength from ultraviolet to visible light?the wavelength less than 512 nm?,and the band gap is about 2.42 eV under room temperature.It can be widely applied in photocatalytic hydrogen production,degradation of organic matter,solar cells,optoelectronic devices and so on.The carriers can move in one direction for CdS nanowires and the photogenerated carriers can also be separated effectively.At the same time,they can improve the photoelectric conversion efficiency by reducing the energy loss of light reflection.Due to the synergistic effect,more and more attention was focused on the CdS nanowires and its heterojunction nanowires.The results showed that the latter have better performance than that of the former in the field of photocatalysis and photoelectric conversion.On the other hand,there is few study of electronic properties in micro region,which is very useful for the better understanding and application of Cd S and its heterojunction nanowires.In this paper,we mainly study the synthesis and electrical properties of one-dimensional Cd S nanowires and CdS/Sn O₂,CdS/Zn O core-shell nanowires.CdS nanowires were prepared by the solvothermal method,and the ZnO or SnO₂ shells were prepared by atomic layer deposition?ALD?technology.The interdigitated electrodes were used to construct CdS related nanowires devices.I-V characteristics behavior and light response were also studied.Different mode of atomic force microscope?AFM?were used to investigate the micro region electrical properties of CdS nanomaterials,such as the surface charge distribution,surface potential and current in longitudinal direction.This paper covers the following three aspects:?1?Synthesis and photoelectric properties of Cd S nanowires.CdS nanowires were prepared by solvothermal method.The morphology and phase analysis results show that the products have uniform size with high purity and good crystallinity.CdS nanowires were assembled onto the interdigitated electrode forming a prototype photoelectric detector.I-V curves and optical response characteristics of CdS nanowire photodetector were studied by using the probe station and the semiconductor tester.The results show that the photocurrent intensity of the device is up to 10^-7 A,and the UV detection switch ratio(I_light/I_dark)of the device is about 10⁵ at 5 V positive bias under 5.8 mW/cm² UV light.The Cd S nanowires were dispersed on ITO substrate and its surface charge distribution was studied by electrostatic force microscopy?EFM?.The surface charge of CdS nanowires were positive and the distribution was uniform.The Fermi level of one single Cd S nanowires was about 4.25 eV from the Kelvin probe microscopy?KPFM?measurement.Conductive AFM showed that the carriers of the CdS nanowires were transported along axial.?2?Synthesis and photoelectric properties of CdS/SnO₂ core-shell nanowires.The SnO₂ shell was deposited on the surface of CdS nanowires by ALD method forming CdS/SnO₂ core-shell nanowires.The properties of UV detection and the micro region electrical properties of CdS/SnO₂ nanowire were studied.When the Sn O₂ was deposited by 90 cycles,the photocurrent intensity of the device is up to 10^-6 A with fast response and recovery time.It also has good stability and wide detection range.Due to the large dark current,the switch ratio was about 10.The electricity in micro region showed that the surface charge distribution of CdS/SnO₂ nanowires was uniform,and the surface potential of CdS/SnO₂ nanowires was obviously changed under illumination.?3?Synthesis and photoelectric properties of CdS/Zn O core-shell nanowires.The ZnO shell nanowires was prepared by ALD on the surface of CdS nanowires forming CdS/Zn O core-shell nanowires.The properties of UV detection and the micro region electrical properties of CdS/ZnO nanowire were also studied.Be compared to the pure CdS nanowires,the photocurrent intensity of the device was up to 10^-5 A from 10^-7 A and the UV switch ratio reached to 10⁷ by increasing two orders of magnitude,which came from the photoinduced charge transfer between CdS and ZnO.The electricity in micro region showed that the surface charge distribution of CdS/Zn O nanowires was uniform,and the surface potential of CdS/ZnO nanowires increased by 100 mV under light.