Indium-doped ZnO Nanowires Research Articles

Indium Dopant Concentration Effects on Zinc Oxide Nanowires.

We report in detail the effects of varying the concentration of indium as a dopant in ZnO on the structural, vibrational, and optical properties of ZnO nanowires. A highly versatile route to dope zinc oxide nanowires by using vapor-liquid-solid growth is employed. It is observed that the ratio of indium in ZnO reactant has a large impact on properties of indium-doped ZnO nanowires. Lower indium concentration reveals better transparency while higher concentrations of indium shows segregation of indium-rich domains within the doped nanocrystals. Photoluminescence measurements demonstrated band gap tuning and a smaller UV to deep emission ratio for doped nanowires. Phonon vibrational modes along with origin of observed anomalous vibrational modes induced due to indium incorporation in ZnO are discussed. An average transmittance of more than 90% is observed for a wide range of spectra in both visible and near-IR regions as compared with indium tin oxide. The lowest resistivity of 1.2 × 10-3 Ω·cm was achieved for ZnO films doped with 7% indium oxide. These dramatically superior optical and electrical properties make it a superior candidate for various technological applications.

Unusual violet photoluminescence in indium-doped ZnO nanowires

Point defects in wide bandgap semiconductors such as ZnO are emerging as promising candidates for single photon sources. However, identification of defect-based luminescence is rather difficult due to the extremely complicated defect physics of ZnO. Here, we report an unusual violet emission centered at 3.1 eV from indium-doped ZnO nanowires. The violet emission can be observed only below 180 K and shows thermal quenching with unexpectedly small activation energy of ∼36 meV. Photoluminescence and X-ray absorption near edge spectroscopy results suggest that the origin of the violet emission is VZn-InZn complex defect. The overall luminescence features can be understood in terms of the configuration coordinate model involving intercross between the potentials of the ground and excited states. Our results may give insights into the defect physics and be essential to the optoelectrical properties of doped ZnO nanostructures.

Indium-doped ZnO nanowires with infrequent growth orientation, rough surfaces and low-density surface traps

Indium-doped ZnO nanowires have been prepared by vapor transport deposition. With increasing In content, the growth orientation of the nanowires switches from [100] to infrequent [023] and the surface becomes rough. No surface-related exciton emission is observed in these nanowires. The results indicate that large surface-to-volume ratio, high free electron concentration, and low density of surface traps can be achieved simultaneously in ZnO nanowires via In doping. These unique properties make In-doped ZnO nanowire a potential material for photocatalysis application, which is demonstrated by the enhanced photocatalytic degradation of Rhodamine B.

Effect of indium concentration on luminescence and electrical properties of indium doped ZnO nanowires

In this work, indium (In) doped ZnO nanowires are grown on a Si substrate by chemical vapor deposition (CVD), at a relatively low temperature of 550°C. The effects of In concentration on the morphology, microstructure, luminescence and electrical properties of ZnO nanowires are investigated. The diameters and lengths of these nanowires are in the ranges of 70–311nm and 10–15μm, respectively. These nanowires are single crystals growing in the [0001] direction. The maximum solubility of In in ZnO is estimated to be 3.47at.%. Photoluminescence (PL) spectra reveal a red shift in the ultraviolet emission and intensity enhancement in the green emission with increasing indium doping concentration. Besides, carrier concentration, mobility and resistivity of the nanowires with different doping concentrations are determined based on single-nanowire field effect transistors (FET).

Quantum-interference transport through surface layers of indium-doped ZnO nanowires

We have fabricated indium-doped ZnO (IZO) nanowires (NWs) and carried out four-probe electrical-transport measurements on two individual NWs with geometric diameters of ≈70 and ≈90 nm in a wide temperature T interval of 1–70 K. The NWs reveal overall charge conduction behavior characteristic of disordered metals. In addition to the T dependence of resistance R, we have measured the magnetoresistance (MR) in magnetic fields applied either perpendicular or parallel to the NW axis. Our R(T) and MR data in different T intervals are consistent with the theoretical predictions of the one- (1D), two- (2D) or three-dimensional (3D) weak-localization (WL) and the electron–electron interaction (EEI) effects. In particular, a few dimensionality crossovers in the two effects are observed. These crossover phenomena are consistent with the model of a ‘core–shell-like structure’ in individual IZO NWs, where an outer shell of thickness t (≃15–17 nm) is responsible for the quantum-interference transport. In the WL effect, as the electron dephasing length Lφ gradually decreases with increasing T from the lowest measurement temperatures, a 1D-to-2D dimensionality crossover takes place around a characteristic temperature where Lφ approximately equals d, an effective NW diameter which is slightly smaller than the geometric diameter. As T further increases, a 2D-to-3D dimensionality crossover occurs around another characteristic temperature where Lφ approximately equals t (<d). In the EEI effect, a 2D-to-3D dimensionality crossover takes place when the thermal diffusion length LT progressively decreases with increasing T and approaches t. However, a crossover to the 1D EEI effect is not seen because LT < d even at T = 1 K in our IZO NWs. Furthermore, we explain the various inelastic electron scattering processes which govern Lφ. This work demonstrates the complex and rich nature of the charge conduction properties of group-III metal-doped ZnO NWs. This work also strongly indicates that the surface-related conduction processes are essential to doped semiconductor nanostructures.

Growth and Characterization of Indium Doped ZnO Nanowires Using Vapor Transport Deposition Method

Indium (In) doped ZnO nanowires (NWs) has been grown on silicon substrate without the use of catalyst. In conventional vapor transport deposition method, the ZnO source powder usually mixed with In dopant and placed in the middle of quartz tube. However, in this work, the graphite mixed ZnO source powder on a crucible was placed at the center of the quartz tube. While the graphite mixed In2O3was placed at the downstream of the furnace with a distance of 1 cm from the graphite mixed ZnO powder. Morphological study has been carried out using field emission scanning electron microscopy (FESEM). The result showed that the grown NWs have uniform hexagonal nanostructures. Chemical composition has been examined by energy dispersive X-ray spectroscopy (EDS). XRD spectrum of the In doped ZnO NWs has also been taken to study the crystallinity of the structure.

Enhanced Photoluminescence and Field-Emission Behavior of Vertically Well Aligned Arrays of In-Doped ZnO Nanowires

Vertically oriented well-aligned Indium doped ZnO nanowires (NWs) have been successfully synthesized on Au-coated Zn substrate by controlled thermal evaporation. The effect of indium dopant on the optical and field-emission properties of these well-aligned ZnO NWs is investigated. The doped NWs are found to be single crystals grown along the c-axis. The composition of the doped NWs is confirmed by X-ray diffraction (XRD), energy-dispersive spectroscopy (EDS), and X-ray photospectroscopy (XPS). The photoluminescence (PL) spectra of doped NWs having a blue-shift in the UV region show a prominent tuning in the optical band gap, without any significant peak relating to intrinsic defects. The turn-on field of the field emission is found to be ∼2.4 V μm(-1) and an emission current density of 1.13 mA cm(-2) under the field of 5.9 V μm(-1). The field enhancement factor β is estimated to be 9490 ± 2, which is much higher than that of any previous report. Furthermore, the doped NWs exhibit good emission current stability with a variation of less than 5% during a 200 s under a field of 5.9 V μm(-1). The superior field emission properties are attributed to the good alignment, high aspect ratio, and better crystallinity of In-doped NWs.

Weak Localization and Electron−Electron Interactions in Indium-Doped ZnO Nanowires

Single crystal ZnO nanowires doped with indium are synthesized via the laser-assisted chemical vapor deposition method. The conductivity of the nanowires is measured at low temperatures in magnetic fields with directions both perpendicular and parallel to the wire axes. A quantitative fit of our data is obtained, consistent with the theory of a quasi-one-dimensional metallic system with quantum corrections due to weak localization and electron-electron interactions. The anisotropy of the magneto-conductivity agrees with theory. The two quantum corrections are of approximately equal magnitude with respective temperature dependences of T(-1/3)and T(-1/2). The alternative model of quasi-two-dimensional surface conductivity is excluded by the absence of oscillations in the magneto-conductivity in parallel magnetic fields.

Synthesis and Characterization of Indium-Doped ZnO Nanowires with Periodical Single−Twin Structures

In-doped ZnO (IZO) nanowires have been synthesized by a thermal evaporation method. The morphology and microstructure of the IZO nanowires have been extensively investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), and high-resolution transmission electron microscopy (HRTEM). The products in general contain several kinds of nanowires. In this work, a remarkable type of IZO zigzag nanowire with a periodical twinning structure has been investigated by transmission electron microscopy (TEM). HRTEM observation reveals that this type of IZO nanowire has an uncommonly observed zinc blend crystal structure. These nanowires, with a diameter about 100 nm, grow along the [111] direction with a well-defined twinning relationship and a well-coherent lattice across the boundary. In addition, an IZO nanodendrite structure was also observed in our work. A growth model based on the vapor-liquid-solid mechanism is proposed for interpreting the growth of zigzag nanowires in our work. Due to the heavy doping of In, the emission peak in photoluminescence spectra has red-shifted as well as broadened seriously.