Synthesis Of Group ?-? Semiconductor Nanotubes And Application In Photodetector

Photodetectors are one of widely used electronic devices for light and radiation signal detection,which can achieve the purpose of detecting light with certain wavelength and special electromagnetic radiation.Nowadays,the rapid development of electronic industries requests the photodetector devices not only have a higher performance,but also possess more integrated level.Therefore,how to design and fabricate photodetector with smaller size and higher performance has become an important issue in future scientific research and electronic technology.My research exhibits the importance of the synergistic combination of active materials synthesis and device structure engineering in the development of higher performance photodetectors.Firstly,CdS semiconductor nanotubes with novel hollow structure were first synthesized using physical vapor deposition(PVD)method and it is further demonstrated the method was still effective to prepare other Groups II-VI semiconductor nanotubes(CdSe and ZnS).It showed that these semiconductor nanotubes possessed a good crystal quality,uniform structure and defects-free character.Compared with the reported researches on the synthesis of semiconductor nanotubes,the PVD method with more simplified procedures is beneficial to synthesize the semiconductor nano tubes with less defect and high-quality crystal.Based on the theoretical analysis and experimental results,we first experimentally demonstrated preferential nucleation VLS mechanism for the growth of semiconductor nanotubes.In the growth process,the nucleation and crystallization of growing semiconductor nanotubes preferentially occurred at the precursor vapor-catalyst liquid-crystal interface(three phase boundaries,TPB).Moreover,it is found the growing temperature not only had effect on increasing the evaporated amount of the precursor but alao played a critical role in modulating the supersaturation of three phase interfaces,which dominateded the structure of the synthesized materials.In addition,wetting angle between the Au catalyst droplet and formed crystal controlled the magnitude of surface energy of different interfance and further resulted in the synthesized semiconductor nanotubes with different thickness.The synthesized semiconductor nanotubes with a novel tubular structure and larger surface-area-to-volume ratio than other one-dimensional nanostructures showed a great potential in the application of photonic and electronic devices.I designed a fully nanostructured mental-semiconductor-mental(MSM)photodetector using the synthesized semiconductor nano tubes as active layer and Ag nanowires as low-resistance electrodes,which really showed higher photodetector performance(larger sensitivity and higher response speed)as compared with other one-dimensional nanostructures(nanowire,nanobelt and nanorod)photodetector.In order to investigate the photodetector performance in single nanotube photodetector,I first successfully fabricated a single nanotube photodetecotor with Ag nanowires as electrodes based on the nanostructure assembly technique,which was not dependent on many expensive instruments and had a simplified process compared with the common microfabrication process.I discovered the interface of single CdSe nanotube and Ag nanowires consisted of large number of nanoscale Schottky contact formed by the CdSe nanotube/Ag nanowire point contacts,which provided a platform to understand the optoelectronics in nanoscale Schottky contacts.Besides,a novel low-dimensional semiconductor materials self-derived photodetector was designed based on the asymmetrical metal-semiconductor-metal(MSM)structure.When the bias voltage was zero,the difference of the two back-to-to back Schtooky barriers induced by the asymmetrical structure of the device provided the driving force for the separation and transportant of photogenerated holes and electrons.Furthermore,it is found that more asymmetry of MSM structure would result in the larger driving force for enhancing the separation of photogenerated carriers and photoresponse speed.The novel self-powered photodetector exhibited a high sensitivity and a fast response speed without any external bias,which provided us a new strategy of designing high-performance self-driven photodetecotor.At last,in our research,on one hand,the traditional contact printing method was improved.One the other hand,it is found that the surface tension,the difference of temperature and solution concentration in and outer region of droplet would result in an evaporation-induced circulation in the droplet,by which a new evaporation-induced circulation assisted self-assembly method was created.Based on the two assembly methods,the synthesized semiconductor nanotubes can be effectively assemblied with high alignment ratio on a large-scale substrate.The alignment semiconductor nanotubes show high potential in the design of higher performance photodetector due to the decreased contact resistance of active layer.