Blueshift of absorption edge and photoluminescence in Al doped ZnO thin films

ABSTRACT

Pure and Al doped ZnO thin films are fabricated on quartz substrates by sol–gel method, and then analyzed by X-ray diffraction (XRD), transmittance spectra, and photoluminescence (PL) measurements respectively. XRD results reveal that all the thin films have a preferential c-axis orientation. With the increase of Al doping, however, the peak position of the (002) plane is shifted to a low 2θ value. On the other hand, the data of spectrometer transmittance are obtained, with which the band gap energies of Al doped ZnO films are calculated by a linear fitting method. The band gap is found to be broadening, and the absorption edge has an obvious blueshift to the shorter wavelength with increasing dopant concentration. PL measurement is also conducted, and deep-level (DL) emission and near band edge (NBE) emission are observed in pure ZnO thin films. But DL emissions are depressed when Al is doped into thin films. And the peak of NBE emission has a blueshift to the region of higher photon energy as the Al concentration increases, a performance which tallies with observations through the optical transmittance data. The study demonstrates that the blueshift of optical properties in the ZnO:Al films, can nevertheless be easily manipulated and managed by controlling dopant concentration, a big plus to the said films in their applications in broadband UV photodetectors with highly tunable wavelength resolution.     

溶胶-凝胶法制备Nb掺杂TiO_2的电化学性能

溶胶-凝胶法制备不同晶型的铌(Nb)掺杂二氧化钛(TiO_2),并对电化学性能进行研究。550℃烧结的锐钛矿相Nb掺杂TiO_2具有良好的电化学性能,循环(1~3 V)50次后,仍有190 mAh/g的比容量。600~700℃烧结的样品为锐钛矿/金红石混合相,随着温度的升高,金红石相的含量逐渐增加,电化学性能逐渐变差。     

凝胶—溶胶法制备掺杂Ni、Mn的LiV3O8

用凝胶—溶胶法,按n( LiV3O8)∶n[LiNiO2(或LiMn2O4)]=12∶1制备了掺杂Ni、Mn的LiV3O8,用XRD、循环伏安和恒流充放电测试对样品进行了分析.掺杂未对样品的晶体结构产生影响;掺杂Mn的样品在1.8～3.8V以0.1C循环,首次放电比容量为387.9 mAh/g,比未掺杂样品的299.9...     

Photosensors based on Ni-doped ZnO/p-Si junction prepared by sol-gel method

A high quality and adherent transparent layer of ZnO thin films were grown on p-type Si substrates to fabricate undoped and Ni-doped ZnO/p-Si heterojunction. The C _Adj ?V and G _Adj ?V plots of the diodes are significantly affected with the frequency and Ni-dopant contents. The interface state density (D _it ) is changed with the frequency and Ni contents. The high value of ideality factor (n) is due to the interface states at the interface of the diode and the effect of barrier inhomogeneities or to the high value of R _s . The transient photocurrent measurements were used to analyze the photoresponse of the diodes. The obtained results indicate that the diodes could be used as an optical sensor especially for the Ni-doped at 0.5 % ZnO/p-Si diode.     

Effects of rapid thermal annealing in different ambients on structural, electrical, and optical properties of ZnO thin films by sol-gel method

We studied the effects of rapid thermal annealing in different ambients on the structural, electrical and optical properties of the sol-gel derived ZnO thin films. All the films after annealing showed highly degree of (002) oriented in the X-ray diffractometry (XRD) patterns. The effects of annealing ambients on electrical properties of the films were studied. Carrier concentration, resistivity and mobility were found to be distinguished after annealed in different ambients. The sample with the lowest resistivity of 0.095 ??·cm and the largest mobility of 105.1 cm²/v·s was achieved after annealing in vacuum. XPS results indicated that more oxygen vacancies existed on the ZnO surface when annealed in vacuum than that in O₂.     

Electrical properties of TiO2 thin films prepared by the sol-gel method

A TiO₂ thin film was prepared by the sol-gel method using a metal alkoxide [Ti(O-i-Pr)₄ tetrasopropoxy titanium: TIPT]. The crystalline form of the film depends on the preparation conditions and the heat treatment temperature. When the ratio (γ) of H₂O to TIPT is 7, the crystalline phase is formed at 400°C; when γ = 2 it is formed at 500°C. The anatase crystal structure was obtained for both γ = 2 and γ = 7. The electrical conductivity of the TiO₂ film increased with the heat treatment temperature.     

Electrical and optical properties of PZT ferroelectric films fabricated by the PVP-assisted sol-gel method

Lead zirconate titanate (PZT) films were deposited on platinized silicon substrates by spin coating using organic macromolecule polyvinylpyrrolidone (PVP) as an additive, which has the hybrid effects, was dispersed uniformly into the sol-gel precursor solution of PZT. The films were coated by spin-coating and then annealed at a proper temperature by repaid thermal processing. PZT ferroelectric films were polycrystalline and perovskite phase structure. The Coercive Field and remnant polarization of the PZT films annealed at 600 °C were 91 kV/cm and 19 μC/cm² respectively. The fatigue resistance properties were improved and the polarization value decreased only 8% of the initial polarization at 10⁸ cycles. The optical properties were measured by spectrophotometer and the band energy was calculated about 3.59eV.     

LiFePO_4/C复合材料的溶胶凝胶法制备及电化学性能

用原位聚合法制备Fe PO4/PANI,以此为前驱体采用溶胶凝胶法制备LiFePO4/C复合材料。采用X射线衍射(XRD)、扫描电镜(SEM)对材料的结构及表面形貌进行表征,采用充放电测试研究材料的电化学性能。结果显示样品具有较好的倍率性能和循环性能,在650℃下合成的样品具有最高放电比容量,0.2 C下放电比容量达到165.8 m Ah/g,接近理论比容量170 m Ah/g。     

LiMn2O4薄膜的溶胶-凝胶法制备及其电化学性质

以醋酸锂、醋酸锰、乙二醇甲醚和乙酰丙酮为原料,采用溶胶 凝胶法制备薄膜锂离子蓄电池正极材料尖晶石LiMn2O4薄膜。用X射线衍射、扫描电镜分析了薄膜的物相和表面形貌,用循环伏安法、充放电和交流阻抗技术研究了薄膜的电化学性能。结果表明该法制备的LiMn2O4薄膜均匀、无开裂,750℃退火5min得到的薄膜的首次放电容量为36μAh/(cm2·μm),经100次循环后每次循环的容量损失为0.037%,薄膜具有良好的电化学性能。     

Optical and electrical properties of ZnO thin film containing nano-sized Ag particles

Low-temperature crystallized ZnO thin film was achieved by sol–gel process using zinc acetate dihydrate and 2-methoxyethanol as starting precursor and solvent, respectively. Ag nanoparticles were prepared with uniform size at 4.4 nm by spontaneous reduction method of Ag 2-ethylhexanoate in dimethyl sulfoxide (DMSO). The optical and electrical properties of ZnO thin films containing various contents of Ag-nanoparticles were monitored. Light scattering and charge emission and scattering behaviors of Ag nanoparticles in ZnO film were found. The incorporation of Ag nanoparticles into Al-doped ZnO film was also investigated. The optical transmittance was not degraded but the increase of electrical sheet resistance was found. The effect of Al-dopant on the transmittance and electrical sheet resistance of ZnO film was found too great to distinguish the positive effect of the incorporation of Ag nanoparticles into Al-doped ZnO thin films.     

Optical and sensor properties of ZnO nanostructure grown by thermal oxidation in dry or wet nitrogen

Zn films on glass were oxidized at 390°C in dry or wet N₂. As-prepared ZnO oxides were characterized by a scanning electron microscope (SEM), an X-ray diffractometer (XRD), a transmission electron microscope (TEN) and photoluminescence (PL) measurements. Gold electrodes were deposited on ZnO films to obtain ZnO gas sensors, which were characterized by exposure to ethanol at room temperature. The results show that the specimen oxidized in dry N₂ exhibits a sharp PL peak at 380 nm whereas that oxidized in wet N₂ exhibits a broad peak at 490 nm. The sensors demonstrate significant sensitivity to ethanol vapor at room temperature with a detection limit of 200 ppm for the sensor with ZnO oxidized in wet N₂. Recovery for the sensor with ZnO oxidized in wet N₂ can be achieved by illumination with natural light. However, for the sensor with ZnO oxidized in dry N₂, ultraviolet (UV) radiation is needed for recovery.     

Effect of preheating process on crystallization and optical properties of sol-gel derived ZnO semiconductor thin films

Highly transparent ZnO semiconductor thin films were deposited onto alkali-free glass substrates by a sol-gel spin coating process. This research investigated the effects of different preheating rates (4 or 10°C/min) on the various surface morphologies, crystallization characteristics, and optical properties of these thin films. The ZnO sol was synthesized by dissolving the zinc acetate dihydrate in isopropanol (IPA), and then adding monoethanolamine (MEA). These as-coated films were preheated at 300°C for 10 min and annealed in an air ambiance at 500°C for 1 h. Experimental results revealed that the as-prepared films had a hexagonal wurtzite structure, and that the heating rates of the preheating process obviously affected the surface morphologies, crystallization qualities, and transparency levels of the thin films. A ZnO thin film preheated at 10°C/min exhibited preferential orientation along the (002) plane, a flat surface, and also achieved a high transmittance value, 92.5%, for light with a wavelength of 550 nm.     

Dielectric properties for Tantalum-doped strontium barium titanate thin films prepared by sol-gel method

In this work, Sr_0.5Ba_0.5Ti_1-zTa_zO₃ (SBT) thin films were prepared on a Pt/SiO₂/Si substrate by sol-gel process. The microstructures of SBT thin films were examined by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). The influences of Ta on the microstructure and dielectric properties of SBT thin films were studied. It is found that tetragonal perovskite crystal grains existed in SBT thin films. Ta⁵⁺ doping fines the grain of SBT thin films. It is found that Ta⁵⁺ doping decreases dielectric loss for SBT thin films.     

Microstructures and dielectric properties of Zn2SnO4 thin films by sputtering from a ZnO doped ceramic target

The dielectric properties of Zn₂SnO₄ thin films with various degrees of ZnO dopant concentration were investigated. Zn₂SnO₄ thin films were prepared using the radio frequency magnetron sputtering. The X-ray diffraction patterns of the 0 and 75 mole % ZnO doped Zn₂SnO₄ thin films revealed that Zn₂SnO₄ is the main crystalline phase, which is accompanied by a little SnO₂ as the second phase. The second phase SnO₂ in specimens vanished when the extent of ZnO additive was increased to 100 mole%. A dielectric constant of 15–40 and a loss factor of 0.10–0.14 of Zn₂SnO₄ thin films were measured at 1 MHz with ZnO dopant concentration in the range of 0–100 mole%.     

Photoconducting properties of Cd0.4ZnO0.6/p-Si photodiode by sol gel method

Al/Cd_0.4ZnO_0.6/p-Si Schottky photodiode was successfully fabricated via sol–gel process. The current–voltage characteristics of the diode were performed in dark and illumination conditions. The electronic parameters of the diode were determined using the thermionic emission theory. The values of ideality factor (n) and barrier height (Φ_B0) values of the diode were found to be about 5.80 and 0.80 eV, respectively. The photocurrent results in the reverse bias of the diode indicate that the current under illumination is higher than the dark current. The capacitance-voltage (C–V) and conductance-voltage (G–V) measurements of the diode were carried out in the range of 50 kHz–1 MHz. The observed decrease in the capacitance and increase in the conductance with the increasing frequency were explained on the basis of interface states. The obtained results indicate that Cd_0.4ZnO_0.6/p-Si junction is a Schottky type photodiode.     

溶胶-凝胶法制备超级电容器用二氧化锰

用溶胶-凝胶法制备超级电容器用二氧化锰( MnO2)电极材料,研究pH值、干凝胶焙烧温度对产物的影响.制备的MnO2为直锰矿型,晶体呈纤维丝状,颗粒结构松散、内部孔道较大,有利于电子传输和离子扩散.在pH值为8.0、干凝胶焙烧温度为350℃时制得的MnO2性能最好.以0.5 mol/L Na2SO4为电解液,制得的MnO2组装电容器,以66.5 mA/g的电流在0～0.8 V进行恒流充放电,比电容达169.05 F/g.     

微波辅助溶胶-凝胶-模板法制备的Ni纳米线

通过两步阳极氧化法制得氧化铝模板,然后在氧化铝模板的纳米孔洞中,用微波辅助溶胶-凝胶-模板法制备出Ni纳米线。分别用XRD、TEM和VSM对样品的相成分、显微结构和磁性进行观察和测量。结果表明,Ni纳米线为面心立方结构,氧化铝模板的孔洞分布均匀,Ni纳米线的直径取决于氧化铝模板纳米孔洞的大小。纳米线具有铁磁性,其易磁化轴平行于纳米线的长轴方向。     

Photoluminescence of ZnO:Ga Thin Films Fabricated by Pulsed Laser Deposition Technique

Highly c-axis oriented Ga-doped ZnO films (GZO) have been grown on sapphire (0001) substrates by pulsed laser deposition (PLD) method. Photoluminescence (PL) spectra indicate that Ga atoms have a large effect on the luminescent properties of ZnO films. PL spectra of GZO films show near band edge (NBE) emissions and broad orange deep-level emissions. The NBE emission shifts to higher energy region and the intensity decreases with the increase of Ga concentration. The blue shift of NBE emission results from Burstein-Moss effect. The quenching of NBE emission is ascribed to the noradiative recombination. The orange emission is related to the oxygen vacancies.     

溶胶-凝胶法合成正极材料LiFePO4

以Fe3 盐为铁源,采用溶胶-凝胶法制备了锂离子电池正极材料LiFePO4,用XRD、SEM、恒流充放电和交流阻抗方法研究了样品的结构、形貌和电化学性能。样品0.1C首次放电容量达到131 mAh/g,经10次循环后,容量保持率为96%。采用溶胶-凝胶法合成的LiFePO4,抑制了循环过程中电化学反应阻抗的增加。     

Thermoelectric properties of silicon nanostructures

Semiconductor nanostructures are promising candidates for efficient thermoelectric energy conversion, with applications in solid-state refrigeration and power generation. The design of efficient semiconductor thermocouples requires a thorough understanding of both charge and heat transport; therefore, thermoelectricity in silicon-based nanostructures requires that both electronic and thermal transport be treated on an equal footing. In this paper, we present semiclassical simulation of carrier and phonon transport in ultrathin silicon nanomembranes and gated nanoribbons. We show that the thermoelectric response of Si-membrane-based nanostructures can be improved by employing the anisotropy of the lattice thermal conductivity, revealed in ultrathin Si due to boundary scattering, or by using a gate to provide additional carrier confinement and enhance the thermoelectric power factor.