First-Principles Investigations For Transport Properties Of Znic Oxide Nanobelts

By using first principles calculations within the framework of density functional theory and noequilibrium green functionals methods, we systematically study the electronic structures and transport properties of one-dimensional ZnO nanobelts, as well as electronic properties and Schottky barriers at metal/ZnO interfaces. We focus on the transport properties of ZnO nanobelts with different transport directions, different widths of nanobelts, strain-modulated transports properties and doping effects. We also investigate the interfacial electronic structures of ZnO nanobelts with several kinds of metals, as well as the relationships between transport and different interfacial spacing. The results are summarized as follows:1. The transport propertis of Cu/ZnO nanobelts/Cu two-probe systems with different transport directions are investigated. The results show the current is asysmetric when ZnO nanobelt is along with [0001] direction, and the current at the negative bias is larger than that at the positive bias. In contrast, the currents are symmetric when ZnO nanobelts are along with non-polarized [1010] and [1210] directions. Additionally, the transport properties with different widths are studied. The narrower nanobelt shows the ohmic-type current, and the wider nanobelt shows the rectifying feature, while the middle size shows the mixed characteristics.2. The interfacial electronic structures between Cu and ZnO nanobelts are investigated. With increasing the interfacial spacing, the interfacial contacts transfer from strong chemical interactions (2.0-2.3A) to weak adsorptions (2.3-3.1A). Moreover, the results show that the energy barriers enhance with the increase of the widths of nanobelts and with the increase of interfacial spacing.3. The strain-modulated electronic structures of ZnO nanobelts are investigated. The band gap shrinks with strain rising up from-5%to5%. Noted that, the change of band gap under tensile and compressive strain is not symmetric, i.e. the change of band gap is much obvious under tensile strains than under compressive strains. The strain-modulated transport properties of ZnO nanobelts are studied. The conductances of narrower nanobelts reduce linearly with the strains, while the conductances of wider nanobelts reduce exponentially with strains. The gauge factors show obvious asymmetric characteristics when the bias is larger than0.6V. When the bias equals to the0.8V, the gauge factors of Cu/ZnO two-probe structures under tensile and compressive strain, are5.6and4.29, respectively. Additionally, the energy barriers as a functional of strains are calculated, and the results demonstrate that the barriers decrease linearly with the strains.4. The transport properties of Al-doped, Ga-doped, In-dpoed, Li-doped, N-doped and P-doped ZnO nanobelts are studied. The results demonstrate that the transport properties of Al-doped and Ga-doped nanobelts are n-type conduct, while the transport properties of Li-doped, N-doped and P-doped nanobelts are p-type conduct. The transport of In-doped nanobelt shows negative resistant effect when the bias are from0.2V to0.7V. The transport properties of Ga-doped ZnO nanobelts with different doping positions are studied. The results demonstrate that the currents gradually reduce with the doping position when they are moving from the middle of nanobelt to the interface. The energy barriers is about0.18eV when the doping positions are in the middle of ZnO nanobelt, while the value is up to0.41eV, when the doping occurs at the interface.5. The electronic structures and energy barriers of the interface among ZnO nanobelts and metal Ag, Al, Au and Pt are investigated. The O-M interface of metal/ZnO(0001) is more energetically preferable than Zn-M interface. The interface of Pt/ZnO(1010) is stable than the interface of Ag-ZnO and Au-ZnO. Furthormore, Schottky contacts can form for Au and Pt when they connect with ZnO(0001)、 ZnO(0001) and ZnO(1010) plane. And Schottky contact is formed for Ag/ZnO, only when Ag contacts with ZnO(0001) plane; on the contrary, ohmic contacts form when Ag connects with ZnO(0001) and ZnO(1010) planes.