Optical and electrical properties of ultralong ZnO nanorod fabricated from preheating hydrothermal method

Ultralong ZnO nanorod arrays with a length of 10 microm were synthesized using a preheated hydrothermal-solution precursor, and their optical and electrical properties were studied using photoluminescence (PL) spectra and field effect transistors (FETs). The PL spectra showed ultraviolet, orange, and red emissions and had different temperature dependences with increasing temperature. The high-resolution photoluminescence spectra showed that the ultraviolet (UV) emission had different origins within different temperature ranges. The parameters describing the temperature dependence of the peak position shift, intensity, and full width at half maximum were evaluated using different models. After the fabrication of individual nanorod FETs, the ultralong ZnO NRs showed a clear n-type gate modulation with a typical electron concentration of 10(17) cm(-3) and a typical electron mobility of 35.7 cm2/V x s.     

Microstructural and optical characteristics of solution-grown Ga-doped ZnO nanorod arrays

Highly oriented Ga-doped zinc oxide (ZnO) nanorod arrays have been prepared on a ZnO-buffered silicon substrate in an aqueous solution, which is a mixture of methenamine (C(6)H(12)N(4)), zinc nitrate hexahydrate (Zn(NO(3))(2)·6H(2)O), and gallium nitrate hydrate (Ga(NO(3))(3)·xH(2)O). The microstructure characteristics and optical properties of the nanorod arrays were analyzed using different characterization techniques including field-emission scanning electron microscopy (FESEM), x-ray photoelectron spectroscopy (XPS), and photoluminescence (PL). The experimental results show that the morphology, density, and surface compositions of ZnO nanorod arrays are sensitive to the concentration of gallium nitrate hydrate. The PL spectra of all ZnO nanorod arrays show three different emissions, including UV (ultraviolet), yellow, and NIR (near infrared) emissions. With the increase in the Ga doping level, the luminescence quality of ZnO nanorods has been improved. The peak of UV emission has a small redshift, which can be ascribed to the combined effect of size and Ga doping. Furthermore, Ga doping has caused defects that respond to NIR emission.     

Growth of well-aligned ZnO nanorod arrays on Si substrates by thermal evaporation of Cu-Zn alloy powders

Well-aligned ZnO nanorod arrays with uniform diameters and lengths have been fabricated on a Si substrate by simple thermal evaporation of Cu-Zn alloy powders in the presence of oxygen without using a template, catalyst, or pre-deposited ZnO seed layer. The ZnO nanorods are characterized by X-ray diffraction, electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy and the growth mechanism is suggested. The nanorods have a single-crystal hexagonal structure and grow along the (0001) direction. Their diameters range from 200 to 400 nm and the lengths are up to several micrometers. The photoluminescence (PL) and Raman spectra disclose the optical properties of the products. The PL spectra show intense near-band ultraviolet emission at 378 nm from the nanorod arrays. The well-aligned ZnO nanorod arrays have a low turn-on field of 6.1 V/microm, suggesting good field emission properties. The simple synthesis methodology in conjunction with the good field emission and optical properties make the study both scientifically and technologically interesting.     

Influence of synthesis temperature on the properties of Ga-doped ZnO nanorods grown by thermal evaporation

This study examined the effect of the synthesis temperatures on the characteristics of vertically aligned Ga-doped ZnO (GZO) nanorods grown on a ZnO template by thermal evaporation using Zn and Ga sources. The increase in synthesis temperature at less than 700 degrees C induced stress relaxation relative to the ZnO template due to the suppression of defect generation by the formation of nanorods, while a further increase resulted in an increase in compressive strain due to dominant Ga doping. The increase in Ga concentration in the GZO nanorods with increasing synthesis temperature was also confirmed by X-ray photoelectron spectroscopy and photoluminescence. The best conductivity was observed in the GZO nanorods grown at 800 degrees C. On the other hand, the GZO nanorods synthesized at 900 degrees C showed less conductivity and weak near-band-edge emission properties due to the generation of defects from the excess Ga.     

Optical and electrical properties of ZnO films deposited by activated reactive evaporation

ZnO films having good transmittance and conductivity were deposited by activated reactive evaporation of Zn metal on glass and Si substrates at room temperature. Optical constants and thickness of ZnO films deposited under different deposition conditions were determined both by spectroscopic ellipsometry (SE) and spectrophotometry. Structural studies showed that the films exhibited a polycrystalline wurtzite structure with the preferential oriented along the (002) plane. Electrical studies by four probe technique showed that the sheet resistance of the films varied from 10⁶ to 50 Ω/square depending upon the oxygen partial pressure used during deposition, and this sheet resistance value increased with time. The increase in sheet resistance with time was found to be dependent on the surface morphology of the film and on the substrate over which they were deposited.     

Influence of thermal annealing on electrical and optical properties of Ga-doped ZnO thin films

Influence of thermal annealing on electrical properties of GZO films has been studied by means of Hall effect measurements and optical characterization based on Drude model analysis for transmission and reflection spectra. Electrical resistivity increased with increasing annealing temperature. Changes of electrical properties were compared between air and N₂ gas atmosphere. Thermal stability in the air was worse compared to the N₂ gas atmosphere. Annealing at rather high temperature caused decrease in the Hall mobility and increase in optical mobility. The difference between the Hall mobility and the optical mobility was attributed to carrier scattering at grain boundaries. Three kinds of deposition method, ion plating using DC arc discharge, DC magnetron sputtering, and RF power superimposed DC magnetron sputtering were compared in terms of the thermal stability.     

Optical,electrical and mechanical properties of Ga-doped ZnO thin films under different sputtering powers

We present the optical, electrical and mechanical properties of Ga-doped zinc oxide (GZO) thin films prepared by radio-frequency (RF) magnetron sputtering at room temperature under different RF powers (80–180 W). The thickness, electron concentration, and electron mobility of the GZO thin film were determined by fitting the visible-to-near-infrared transmittance spectrum of GZO film/glass using the transfer matrix method. The bending force per unit width was measured by a home-made Twyman–Green interferometer with the fast Fourier transform method. The obtained results show that the optical, electrical and mechanical properties of GZO thin film are subject to the RF power. At an RF power of 140 W, the local minimum of bending force per unit width corresponds to the highest electron mobility in GZO thin film. This study demonstrates that the optical, electrical and mechanical properties of GZO thin film can be fully resolved by non-contact optical methods.     

Influence of the substrate temperature on the optical and electrical properties of Ga-doped ZnO thin films fabricated by pulsed laser deposition

Ga-doped (5 wt%) zinc oxide (GZO) thin films were fabricated on corning 1737 substrates at a fixed oxygen pressure of 200 mTorr at various substrate temperatures (100–300 °C) by using pulsed laser deposition (PLD) in order to investigate the microstructure, optical, and electrical properties of the GZO thin films. It was observed that all the thin films exhibit c-axis orientation and exhibit only a (002) diffraction peak. The GZO thin film, which was fabricated at 200 mTorr and 300 °C, showed the highest (002) orientation, and the full width at half maximum (FWHM) of the (002) diffraction peak was 0.38°. The position of the XRD peak shifted to a higher angle with increase in the substrate temperature. The optical transmittance in the visible region was greater than 85%. The Burstein-Moss effect, which causes a shift toward a high photon energy level, was observed. The electrical property indicated that the highest carrier concentration (2.33 × 10²¹ cm⁻³) and the lowest resistivity (3.72 × 10⁻⁴ Ωcm) were obtained in the GZO thin film fabricated at 200 mTorr and 300 °C.     

Preparation and electrical properties of Ga-doped ZnO nanoparticles by a polymer pyrolysis method

In this article, preparation of Ga-doped zinc oxide (GZO) nanoparticles by a polymer pyrolysis method is reported. The pyrolysis behaviors of the polymer precursors prepared via the in situ polymerization of metal salts and acrylic acid are analyzed using thermalgravity-differential scanning calorimetry (TG-DSC) techniques. Then, the structural characteristics of the products are studied by X-ray diffraction (XRD) and transmission electron microscopy (TEM). It is revealed by the results that the GZO nanoparticles calcined at 600 °C show good crystallinity with the wurtzite structure. GZO nanoparticles doped with 4 mol% Ga have a mean particle size of 26 nm with spherical-like morphology. Electrical resistivity measurement shows that, before and after high temperature annealing under H₂ atmosphere, the resistivity of the GZO nanoparticles is decreased by one and four orders in magnitude, respectively, compared with the pure ZnO nanoparticles. In addition, due to its versatility, this in situ polymer pyrolysis method can be easily extended to synthesis of other n-type doped semiconductor, such as In and Al doped ZnO or Sb doped SnO₂.     

水热法制备掺铝氧化锌纳米棒阵列及其光学特性

采用水热法,在ZnO种子层上制备出不同Al掺杂量的ZnO纳米棒阵列薄膜,利用XRD、SEM、TEM、PL等检测手段对样品进行结构、形貌和发光性能分析.结果表明,纳米棒属于六方纤锌矿结构,具有垂直基底沿[002]方向生长的特征,PL谱上存在强的近紫外辐射峰.随着掺杂量的增加,纳米棒直径略有减小,近紫外辐射峰蓝移,强度先增加后减小,证明掺杂会形成非辐射中心,探讨了Al掺杂ZnO纳米棒阵列的发光机理.     

Structural, electrical and moisture resistance properties of Ga-doped ZnO films

The structural, electrical and moisture resistance properties of Ga-doped ZnO (GZO) films with 200 nm thickness in terms of their dependence on oxygen gas flow rate (fO₂) during deposition were studied. GZO films are deposited on glass substrates by ion plating with DC arc discharge. After a reliability test at a temperature of 60 °C and a relative humidity of 95% for 500 h, the percentage of resistivity change of GZO films decreased from 16–20% to 3–11% with increasing fO₂ from 6–12 to 14–25 sccm. The minimum percentage of the resistivity change was observed in the GZO films deposited at fO₂ of 21 sccm and the resistivity after the reliability test was 3.5 × 10^{− 4} Ω cm. The effects of the intrinsic defects on the percentage of resistivity change are discussed on the basis of electrical and optical characteristics of GZO films.     

Controllable synthesis and photoluminescence properties of ZnO nanorod and nanopin arrays

Well-aligned ZnO nanorods and nanopins are synthesized on a silicon substrate using a one-step simple thermal evaporation of a mixture of zinc and zinc acetate powder under controlled conditions. A self-assembled ZnO buffer layer was first obtained on the Si substrate. The structure and morphology of the as-synthesized ZnO nanorod and nanopin arrays are characterized using X-ray diffraction, and scanning and transmission electron microscopies, energy-dispersive X-ray spectroscopy, and photoluminescence spectroscopy. The influence of the background atmosphere on the two ZnO nanostructures has been studied. Two different growth mechanisms are mentioned to interpret the formation of ZnO nanorod and nanopin arrays in our work. The room-temperature PL features the ZnO nanorods exhibit only sharp and strong ultraviolet (UV) emission emissions, which confirms the better crystalline and optical quality than the ZnO nanopins.     

Vertically aligned Fe-doped ZnO nanorod arrays by ultrasonic irradiation and their photoluminescence properties

A facile sonochemical route was demonstrated for the direct fabrication of Fe-doped ZnO nanorod arrays on a Si substrate under ambient conditions. By adding Fe³⁺ ions in reaction solution, Fe is readily in situ doped into ZnO nanorod arrays via ultrasound irradiation. The morphology and structural characteristic of the Fe-doped ZnO nanorods were investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). And crystal structure was characterized by X-ray diffraction (XRD) spectroscopy. Inductively-coupled plasma atomic emission spectroscopy (ICP-AES) confirmed the Fe-doping of ZnO nanorod arrays with a concentration of 0.9 wt.%. In addition, Fe-doped ZnO nanorod showed the enhancement of photoluminescence (PL) intensity in green-yellow emission.     

ZnO纳米棒阵列、纳米片及其发光和光催化特性

首先通过溶胶-凝胶法在Si片基底上制备1层ZnO纳米薄膜,作为纳米棒的晶种层,然后利用金属浴沉积法在ZnO纳米薄膜基础上制备择优取向的ZnO纳米棒阵列,最后通过水热法二次成核结晶形成纳米片。研究证明,ZnO纳米棒阵列和纳米片均沿着c轴取向。在Cu2+抑制极性面生长的作用下,形成的ZnO纳米片结构均匀,分布面积广,单片ZnO纳米片的厚度约为8 nm,面积呈平方微米级,较大的有40μm2左右。ZnO纳米结构的生长取向对其物理化学性能具有重要影响。高度沿c轴取向的ZnO纳米棒有利于紫外光发射和激光器的发展,但极性面的缩小不利于光催化反应。     

Optical properties of NiO thin films fabricated by electron beam evaporation

Nickel oxide (NiO) thin films were deposited onto quartz substrates by the electron beam deposition technique, and obtained high crystal quality after annealing at 1173 K. The structural and microstructural properties of the films were studied by X-ray diffraction (XRD) and atomic force microscope (AFM), respectively. We focus on the optical characterization of the films, indicating the enhancement of the crystal quality, which was confirmed by the photoluminescence and Raman spectrum. Furthermore, PL studies exhibited room temperature emission at 377 nm, and also shown high ultraviolet/visible rejection ratio (>100).     

Changes in electrical and optical properties of polycrystalline Ga-doped ZnO thin films due to thermal desorption of zinc

Influences of thermal desorption of Zn atoms on electrical and optical properties of Ga-doped ZnO (GZO) films deposited by ion plating with direct current arc discharge have been studied. The amount of Zn desorption was controlled by thermal desorption spectroscopy. The resistivity of the GZO films was not affected by the thermal desorption of Zn up to the heating temperature of 300 °C, however, the carrier concentration and the Hall mobility showed remarkable changes. The carrier concentrations decreased with increasing the Zn desorption, and the Hall mobility increased. The decrease in carrier concentration showed strong correlation with the desorption of Zn atoms from the GZO films. The transparency in near infrared wavelength region increased without change of resistivity due to the decrease in carrier concentration.     

Effect of Sn doping on structural, optical, electrical and wettability properties of oriented ZnO nanorod arrays

Herein we present a modified sol gel route for the one step fabrication of oriented ZnO nanorod arrays. The method is seed layer free, and nanorods directly attach to a substrate. We also present the effect of tin (Sn) content on the crystallinity, microstructural, optical and electrical properties of the ZnO nanorod arrays. Thermo gravimetric (TG) curves of gel precursors showed that most of the organic groups and other volatiles were removed at about 450 °C. X-ray diffraction patterns confirmed that the films were polycrystalline in nature with (002) preferred orientation. The texture coefficient, grain size, dislocation density and lattice parameters of the ZnO arrays were determined. The SEM micrographs revealed that the undoped and 1 at.%Sn doped films were composed of nanorods and the concentration of 2 at.%Sn doping hindered the rod like structure growth and modulated into granular nature. UV-visible transmission spectroscopy indicated that the transparency of the films increased with Sn content. On Sn doping, the films also exhibited a red shift and slight shrinkage of band gap. The electrical studies revealed that 1 at.% of Sn doping enhanced electrical conduction in ZnO films and beyond that the distortion caused in the lattice reduced the conductivity. The contact angle of the ZnO nanostructures varied between 91° and 115° depending upon the Sn content. Therefore, 1 at.%Sn doping into ZnO nanorods improves the crystallinity, electrical conductivity and water contact angle.     

ZnO nanorod arrays for photoelectrochemical cells

The splitting of water using photoelectrochemical (PEC) cells to produce hydrogen is one of the most sustainable forms of energy production and more and more 1-D nanostructrues semiconductors used as photoelectrodes have been studied extensively. However, it is not clear whether the photoconversion efficiencies of such nanostructure devices are limited by the architectures of the 1-D electrodes. Here, we explore the effect of the architecture like the length and width of ZnO nanorods on the PEC cells performance for the first time. The as-prepared nanorods have diameters of 40-50 nm and lengths of 400-800 nm. Preliminary measurements exhibit that the resulting electrodes have promising PEC properties. Mott-Schottky measurements give a flat-band potential of +0.10 V, a carrier density of 3.7 x 10(17) cm(-3), and a space-charge layer of 26 nm. The photocurrent of 800 nm-long nanorods shows 10 times higher than that of 400 nm-long ones, and an encouraging maximum photoconversion efficiency of 0.25% is obtained under illumination of 100 mW/cm2 (AM 1.5), which is among the highest reported for an undoped ZnO photoelectrode to date.     

Effect of thermal annealing on electrical properties of transparent conductive Ga-doped ZnO films prepared by ion-plating using direct-current arc discharge

The effect of thermal annealing on the electrical properties of highly transparent conductive Ga-doped ZnO (GZO) films deposited on glass substrates at 200 °C by an ion-plating deposition was investigated. GZO films were annealed in the temperature range from 200 to 600 °C for 30 min under the atmospheric pressure of high-purity N₂ gas. Up to 300 °C, GZO films were electrically very stable, and there was little change in resistivity. When the annealing temperature exceeded 400 °C, resistivity increased rapidly, originating from an abrupt decrease in carrier concentration. It was suggested to be due to both desorption of Zn from GZO films and grain boundary segregation of Ga dopants.