Manipulation Of Interfacially Doped ZnO Nanowires And Polarized Photoresponse Of BP/InSe Heterojunctions

Low-dimensional systems,in which one or more spatial dimensions are small enough to restrict the quantum mechanical wave-function of carriers contained inside,exhibit many intriguting physical phenomena such as small size effect,surface effect,quantum tunneling and Coulomb blockade effect.As a consequence,compared with traditional three-dimensional systems,low-dimensional systems show diverse properties in mechanics,optics,electronics and thermotics.Moreover,the interface between the low dimensional materials and（or）electrodes is crucial for the performance of the device.In this context,study of low-dimensional systems can not only deep our understanding for the unknown areas,but also play a major role in designing and optimizing the devices in the future.In this dissertation,we would take one-dimensional ZnO nanowires and two-dimensional layered materials（such as BP,InSe and Bi₂Te₃）as examples to investigate the influence of interfacial doping on the quantum transport properties of ZnO nanowires,the opto-electrical properties of BP/InSe heterojunctions and the transport properties of the grown Bi₂Te₃ flakes.The contents of the dissertation are summarized as follows.In chapter one,we firstly introduced the structure,synthesis methods and the development of research on optics,electronics and opto-electronics for low-dimensional materials（including ZnO nanowires and two-dimensional layered materials）.Then we presented the significance and contents of our research.In chapter two,we carefully prepared interfacial Al-doped（IAD）and interfacial natively-doped（IND）ZnO nanowires（NWs）by introducing atomic-layer interfacial-doping between the two steps of CVD growth.Variable-temperature electron transport as well as magneto-transport behaviours of these NWs were systematically investigated.We found that interfacial Al doping could turn the electrical property of IND ZnO NWs from semiconducting to metallic.By virtue of the unique architecture and the quality-guaranteed growth technique,a series of quantum interference effects were clearly observed in the IAD ZnO NWs,including weak localization,universal conductance fluctuation.Due to the suppressed electron-phonon scattering,the phase-coherence length（L_φ）of electrons exceeds 100 nm in the IAD ZnO NWs,much longer than those in the IND ones and most conventionally doped ZnO NWs.Apart from that,we also found conspicuous Altshuler-Aronov-Spivak（AAS）oscillation at the IAD NWs with the diameter of tubular interfacial layer compared to L_φ,which was the evidence of the tubular conducting interface.In chapter three,we constructed a vertical p-n diode by vertically stacking p-type few-layer black phosphorus（BP）on n-type few-layer indium selenide（InSe）.The prepared heterojunction exhibited an obvious gate-modulated rectifying effect in the dark（the rectification ratio could reach as high as 180 at-15V gate voltage）.More importantly,by taking advantages of the strong linear dichroism of BP,the device demonstrated a highly polarization-sensitive photocurrent with the anisotropy ratio as high as 0.83.In addition,because of the small band gap as well as the high intrinsic carrier mobility of BP and InSe,the heterojunction displayed a broadband（from visible to infrared）and fast（20-30ms）photoresponse under illumination.Moreover,the device could work in a zero-bias photovoltaic mode.We also proved that the photocurrent,responsivity and external quantum efficiency could be further modulated by the back gate.In chapter four,we successfully fabricated(BixSb_1-x)₂Te₃ flakes on both fluorine mica and SiO₂ substrates through vapor phase condensation method.The nucleation density,size and thickness of the(BixSb_1-x)₂Te₃ flakes could be further tuned by changing the temperature of substrates and pressure during the growth.Additionally,through the method of regowth,we fabricated the inkslab-shaped(BixSb_1-x)₂Te₃/Sb₂Te₃ heterostructures.Most importantly,we performed systematical transport measurements on the grown Bi₂Te₃ flakes.The nature of metal-semiconductor transition and weak antilocalization effect were observed clearly,and two separated two-dimensional topological surface states existed in the Bi₂Te₃ flake can be safely confirmed by analyzing the weak antilocalization effect.Moreover,the behavior of Shubnikov-de Haas oscillations can be observed at 2K for the Bi₂Te₃ flake,indicating its non-trivial topological insulator and existence of the Dirac Fermion on the topological surface states.In chapter five,we presented the current challenges of the low-dimensional systems and a brief outlook for the ongoing work.