Study On Fast And Controllable Preparation Of Wafer-scale Semiconducting Carbon Nanotube Film And Its Electrical And Optoelectronic Performance

As a quasi-one-dimensional direct bandgap semiconductor,semiconducting single-wall carbon nanotubes(SWCNTs)have high carrier mobility,high light absorption efficiency,and adjustable bandgap depending on their structure,making them ideal materials for high-performance electronic and optoelectronic devices.At present,researches on the application of SWCNTs in electronic and optoelectronic devices are mainly focused on individual SWCNT or mixed chirality SWCNT films.However,it is difficult to accurately characterize the SWCNT chirality and performance of an individual SWCNT device due to its weak optical and electrical signals.For the SWCNT film with a mixed structure,the performance of the device is difficult to be predicted due to the diversity of the chirality structure,and the performance variance between devices is larger,which seriously hinders the studies of properties and applications of SWCNTs.In this thesis,mainly based on the separation of single chirality SWCNTs by gel chromatography,we developed a rapid preparation technology of wafer-scale uniform SWCNT film,constructed semiconducting SWCNT thin film field effect transistors(TFT)with different chirality structure,and studied the dependence of the electrical performance of SWCNTs on their chirality structure.In addition,we systematically researched the way to improve the performance of SWCNT thin film photodetectors.The main content of this thesis includes the following aspects:We developed alkaline small molecule control technology,enhanced the interaction between SWCNTs dispersed in aqueous solution and amine-functionalized substrate,and realized the rapid preparation of wafer-scale uniform SWCNT films.By introducing alkaline small molecules such as Na HCO₃ or Na OH into the surfactant-dispersed SWCNT aqueous solution,the density of the surfactant molecules wrapped on the surface of the SWCNT is reduced,and the adsorption of the surfactant molecules on the amine-functionalized substrate of the device is inhibited.Thus,the enhancement of the adsorption between the SWCNTs and the device substrate is realized.With this technology and increasing the concentration of the SWCNT solution,we can quickly prepare a SWCNT film with a density of 30 tubes/?m in a wafer area within 1 second.As the deposition time increasing,the density further increases.The characterization of morphology,optical,electrical,and optoelectronic properties verified the density and performance uniformity of the prepared semiconducting SWCNT film in the range of wafer scale while the use of single chirality SWCNTs further improved the uniformity of the electrical performance of the film.Moreover,this technology is suitable for various flexible and rigid substrates,which effectively expands the application range of SWCNTs.This work lays a foundation for studying the influence of chirality on the electrical properties of SWCNT films and the application of SWCNTs in electronic and optoelectronic integrated circuits.On the basis of uniform SWCNT film preparation,the effect of SWCNT density on the performance of TFT was studied.It was found that as the density increasing,the conductivity and switching performance of TFT were counterbalanced,so the appropriate density was selected to further study the influence of gate structure and dielectric layer materials on the performance of SWCNT TFTs.We will choose different gate structure TFTs according to different research and application requirements.The top-gate structure TFT was used to study the dependence of the electrical performance of 11 kinds single chirality SWCNT on their chirality structure.It is found that their performance is not only related to the diameter,but also closely related to the chiral angle and Type of SWCNTs.In particular,for Type I SWCNTs,the TFT performance of SWCNTs belonging to same Family becomes better as the chiral angle increases,while for Type II SWCNTs,the TFT performance becomes worse as the chiral angle increases.By analyzing intrinsic band gap of SWCNTs,the height of the contact barrier with the metal electrode,the overlap barrier of intertubes,and the intrinsic transport properties of innertubes in the network film,the effect of chirality on the performance of TFTs was explained.Based on high-density and uniform semiconducting SWCNT films,we further constructed composite thin film photocurrent detector and p-n junction photovoltaic detector.The results demonstrate that by constructing a composite thin film photocurrent detector with C₆₀ film,the responsivity of the detector can be effectively improved and the application of the device under low operating voltage can be expanded compared with SWCNT detector.The amplitude of the increase is related to the wavelength of the incident light,and it is found that the composite thin film device exhibits peculiar negative photoconductivity under short-wavelength laser and high source-drain voltage.Therefore,the device can be used as a multi-band high-sensitivity detector.Besides,we built a photovoltaic detector by forming a p-n heterostructure in the channel of the SWCNT TFT through segmentally doping.The photovoltage can reach 80 m V under weak white light,and the photovoltage responsivity exceeds 10⁶ V/W.And benefiting from the high uniformity of SWCNT films,the device shows very good cascading performance.When we connected to the side-gate TFT with the ionic liquid as the dielectric layer and cascading photovoltaic detector,a simple optoelectronic integrated unit can be constructed,which can realize the function of signal conversion and amplification.At the same time,the incident light can be used as a switch to achieve three orders of magnitude adjustment of the source and drain current of the TFT.