Tuning Electrical And Optical Properties Of One-Dimensional Semiconductor Nanostructures Via Surface Charge Transfer Doping

One-dimensional(1D)semiconductor nanostructures have advantages of large specific surface area,unique photoelectric properties,and easy integration compared with bulk materials.Therefore,they are ideal building blocks for high-performance optoelectronic devices.Small-molecule organic semiconductor nanostructures have been favored in smart wearable devices because of their low cost and flexibility.However,their application in optoelectronic devices is limited due to the relatively low carrier concentration and mobility.Other than this,the practical application of inorganic semiconductor nanostructures with high carrier concentration and mobility also depends on the effective regulation of their electrical and optical properties.In this study,1D small-molecule organic nanostructures and inorganic II-VI nanostructures were prepared by solution-dragging method and chemical vapor deposition method,respectively.Electrical and optical properties of semiconductor nanostructures were tuned via surface charge transfer doping(SCTD).Research contents are as follows:(1)Electrical properties of p-type 1D small-molecule organic nanostructures were regulated by surface modification of MoO3.Large-area growth of p-type small-molecule organic material 6,13-bis(triisopropyl-silylethynyl)pentacene(TIPS-PEN)single-crystal nanoribbons(NRs)arrays were realized by dragging a blend solution of TIPS-PEN and polystyrene(PS)on water surface.The modulation of electrical properties of TIPS-PEN NRs was implemented by thermal deposition of p-type MoO3.The carrier mobility(0.708 cm2/Vs),threshold voltage(1.9 V),on/off ratio(105)were improved by optimizing doping regions.The hole injection efficiency between electrode and TIPS-PEN was enhanced by delocalized holes on the surface of TIPS-PEN.(2)Electrical properties of 1D n-type small-molecule organic nanostructures were tuned via SCTD by LiF.N-type 6,13-bis((triisopropylsilyl)ethynyl)-5,7,12,14-tetraazapentacene(TIPS-TAP)single-crystal NRs were fabricated by solution-dragging method.Surface modification of LiF greatly improved the electrical performance of TIPS-TAP based organic field effect transistors(OFETs).On/off ratio increased from 102 to 105 to a large extent,carrier mobility increased from 0.0008 to 0.045 cm2/Vs,and threshold voltage was adjusted from 29.4 to 17.8 V.The charge transfer process between LiF and TIPS-TAP decreased the contact barrier between TIPS-TAP and electrode,which was confirmed by X-ray photoelectron spectroecopy.(3)Electrical and Raman properties of cadmium sulfide(CdS)NRs tuned by SCTD were studied.Electron depletion and accumulation in CdS NRs were achieved by using MoO3 with high work function and benzyl viologen(BV)with strong reducing capability as surface dopants,respectively.Through controlling the density of surface dopants,resistivity as well as electron concentration of the CdS NRs could be effectively modulated.In addition,Due to the strong electron-phonon coupling effect,the optical phonon modes in the Raman spectra of CdS NRs tended to shift positively(or negatively)with electron accumulation(or depletion).A new mechanism based on the semi-classical longitudinal-optical-phonon-plasmon(LPP)theory was proposed to explain the SCTD-induced Raman scattering modulation.