磁控溅射法制备ZnO/YBCO异质结及电学特性

利用磁控溅射技术在YBCO上沉积ZnO薄膜,获得ZnO/YBCO异质结.测量其不同温度下的电学性质,样品显示良好的整流特性,并且随着温度的升高,ZnO/YBCO异质结电流逐渐增大.     

电泳法制备ZnO/YBCO异质结及电学性质研究

采用电泳方法及高温煅烧工艺制备ZnO/YBCO异质结,XRD图谱显示ZnO具有c轴方向的择优取向。在SEM的截面图中可观察到ZnO与YBCO结合致密,放大500倍的表面形貌图呈现织构(textured)的微结构特征,放大5000倍的表面形貌图中可观察微米量级的六方晶粒。通过对ZnO/YBCO异质结的电学性质进行测试,结果显示整流特性。     

Effect of doping on structural,optical and electrical properties of nanostructure ZnO films deposited onto a-Si:H/Si heterojunction

We investigated the structural; optical and electrical properties of ZnO thin films as the n-type semiconductor for silicon a-Si:H/Si heterojunction photodiodes. The ZnO film forms the front contact of the super-strata solar cell and has to exhibit good electrical (high conductivity) and optical (high transmittance) properties. In this paper we focused our attention on the influence of doping on device performance. The results show that the X-ray diffraction (XRD) spectra revealed a preferred orientation of the crystallites along c-axis. SEM images show that all films display a granular, polycrystalline morphology and the ZnO:Al exhibits a better grain uniformity. The transmittance of the doped films was found to be higher when compared to undoped ZnO. A low resistivity of the order of 2.8 × 10⁻⁴ Ω cm is obtained for ZnO:Al using 0.4 M concentration of zinc acetate. The photoluminescence (PL) spectra exhibit a blue band with two peaks centered at 442 nm (2.80 eV) and 490 nm (2.53 eV). It is noted that after doping the ZnO films a shift of the band by 22 nm (0.15 eV) is recorded and a high luminescence occurs when using Al as a dopant. Dark I–V curves of ZnO/a-Si:H/Si structure showed large difference, which means there is a kind of barrier to current flow between ZnO and a-Si:H layer. Doping films was applied and the turn-on voltages are around 0.6 V. Under reverse bias, the current of the ZnO/a-Si:H/Si heterojunction is larger than that of ZnO:Al/a-Si:H/Si. The improvement with ZnO:Al is attributed to a higher number of generated carriers in the nanostructure (due to the higher transmittance and a higher luminescence) that increases the probability of collisions.     

Al/AlO_x/Al隧道结简化制备技术

研究了一种在高阻硅衬底上Al/Al Ox/Al超导隧道结简化制备技术。通过一次光刻镀膜完成隧道结结区的确定和上引线的制备,工艺流程简单重复。在0.3K温度下测量了隧道结样品的I-V特性,能隙电压Vg为0.37m V,超导临界电流密度约为12A/cm2。     

ZnO/Si异质结的光电转换特性研究

利用直流反应溅射方法在p型Si衬底上生长掺Al的n型ZnO薄膜,测量了由n型ZnO薄膜和p型Si衬底组成的异质结在黑暗和光照条件下的I-V特性,结果表明该异质结具有优良的整流特性,而且在光照条件下的反向电流迅速增大并很快趋于饱和.通过测量ZnO薄膜的光电流和异质结的光电压的光谱响应,初步分析了异质结的光电转换机理.测量结果显示,在入射光波长为380nm时光电流强度明显下降,反映出光电流与ZnO薄膜禁带宽度的密切关系;同时还发现,在与ZnO禁带宽度相对应的波长前后所产生的光生电压方向相反.推测这一现象与异质结的能带结构密切相关. 关键词： ZnO薄膜 异质结 光电转换 光谱响应     

Effect of bi-layer ratio in ZnO/Al2O3 multilayers on microstructure and functional properties of ZnO nanocrystals embedded in Al2O3 matrix

Zinc oxide (ZnO) nanocrystals (NCs) embedded in alumina (Al₂O₃) matrix were produced via rapid thermal annealing (RTA) of pulsed laser deposited ZnO/Al₂O₃ multilayered nanostructures. The effect of the thickness ratio (R) between Al₂O₃ and ZnO in one bi-layer on the microstructure and functional properties of NCs has been investigated. Grazing incidence small angle X-ray scattering confirmed the formation of nanocrystals after RTA. Grazing incidence wide angle X-ray scattering studies revealed that ZnO NCs have a high crystalline quality with (100) as preferred orientation. Tensile strain of NCs decreases with increasing R and is correlated to the distribution of NCs. From Raman analysis, it is noticed that the phonon frequency of the E₂ mode, related to the ZnO wurtzite phase, in NCs is shifted towards that of bulk ZnO with increasing R. Photoluminescence studies revealed that the near edge peak position shifts from 382 nm to 371 nm as the ratio R changes from 1.5 to 4 and is attributed to the strain effect. The intensity of emission in the yellow–green region due to defects decreases significantly with increasing R. Current–voltage (I–V) characteristics of Al/ZnO NCs embedded in Al₂O₃/n-Si (100)/Al have shown a hysteresis behavior. The increasing width of the hysteresis with increasing R revealed that the origin of the hysteresis might be due to the existence of polar surface charges on well-separated NCs. The high-resistance and low-resistance states in I–V hysteresis curves seem to be governed by Fowler–Nordheim tunneling and Schottky emission mechanisms, respectively.     

Effect of substrate and annealing on the structural and optical properties of ZnO:Al films

ZnO:Al thin films with c-axis preferred orientation were deposited on glass and Si substrates using RF magnetron sputtering technique. The effect of substrate on the structural and optical properties of ZnO:Al films were investigated. The results showed a strong blue peak from glass-substrate ZnO:Al film whose intensity became weak when deposited on Si substrate. However, the full width at half maxima (FWHM) of the Si-substrate ZnO:Al (0 0 2) peaks decreased evidently and the grain size increased. Finally, we discussed the influence of annealing temperature on the structural and optical properties of Si-substrate ZnO:Al films. After annealing, the crystal quality of Si-substrate ZnO:Al thin films was markedly improved and the intensity of blue peak (∼445 nm) increased noticeably. This observation may indicate that the visible emission properties of the ZnO:Al films are dependent more on the film crystallinity than on the film stoichiometry.     

Effect of crystallinity of ZnO buffer layer on the properties of epitaxial (ZnO:Al)/(ZnO:Ga) bi-layer films deposited on c-sapphire substrate

Bi-layer ZnO films with 2 wt.% Al (AZO; ZnO:Al) and 4 wt.% Ga-doped (GZO; ZnO:Ga) were deposited on the ZnO buffered and annealed ZnO buffered c(0 0 0 1)-sapphire(Al₂O₃) substrates respectively by Pulsed Laser Deposition (PLD). The effect of crystallinity of ZnO buffer layer on the crystallinity and electrical properties of the AZO/GZO bi-layer thin films was investigated. It was seen that the crystallinity of ZnO buffer layer had a great influence on the orientation and defect density of AZO/GZO bi-layer thin films from X-ray Diffraction (XRD) peaks and High Resolution Transmission Electron Microscopy (HRTEM) images. In a word, it was found in the films that more preferred c-axis orientation texture and reduction of the defects such as stacking faults and dislocations, with increasing of the crystallinity of ZnO buffer layer.     

Effect of thickness of CdTe/Ge heterojunction photodetectors on optoelectronic properties

The influence of the thickness of CdTe/n-Ge heterojunction photodetectors on I–V curves was studied experimentally and theoretically. The thicknesses of the CdTe thin films were 110, 130, 150, and 200 nm. The power intensity of illumination was 150 mW/cm². Increasing the thickness led to an increase in photocurrent.     

Preparation and characterization of the ZnO:Al/Fe65Co35/ZnO:Al multifunctional films

The ferromagnetic transparent conducting film is a multifunctional film which has high visible transmittance, low resistivity and room-temperature ferromagnetism, simultaneously. In this article, ferromagnetic transparent conducting ZnO:Al/Fe₆₅Co₃₅/ZnO:Al multilayer films were fabricated by inserting a middle magnetic Fe₆₅Co₃₅ layer into aluminum-doped zinc oxide (ZnO:Al) matrix using a magnetron sputtering apparatus at substrate temperature ranging from room temperature (RT) to 400^∘C. The total film thickness was about 400 nm and the middle Fe₆₅Co₃₅ alloy layer was 4 nm. The influences of substrate temperature (T _s ) on the structural, electrical, optical and magnetic properties of the multilayer films were systemically investigated. The results showed that the microstructure and performance of the composite multilayer films strongly depended on the substrate temperature. The present results also showed that the inserted middle Fe₆₅Co₃₅ alloy thin layer played an important role in providing the RT ferromagnetism and decreasing the resistivity of the multilayer films. Therefore, it is possible to obtain a multifunctional film material with the combination of good optical transparency, high electrical conductivity and RT ferromagnetism.     

ZnO:Al/p-Si的接触特性

利用射频磁控溅射制备了ZnO：Al／p—Si接触,并对其进行C-V和I-V特性的77～350K变温测量。并对未热退火和800℃热退火两种样品的测量结果进行了对比分析。结果发现,未经热退火和经过热退火处理的样品在C—V和I-V特性上有很大差别。解释了两种样品的C—V和I-V测量结果的不同。对于未退火的样品,由于界面处的大量界面态的屏蔽作用,使得ZnO：Al／p—Si异质结的C—V曲线发生畸变。经800℃热退火,ZnO：Al／p—Si异质结的C—V特性恢复正常,说明热退火已经消除了异质结中的界面态和缺陷态。研究表明ZnO：Al／p—Si异质结经适当热退火处理有更好的整流特性同时对光致发光也更有利。     

Influence of strain/stress on the nonlinear-optical properties of sprayed deposited ZnO:Al thin films

Nanocrystalline ZnO:Al thin films were deposited by reactive chemical pulverization spray pyrolysis technique on heated glass substrates at 450 °C to study their crystalline structure, composition, strain, stress, roughness characteristics and nonlinear optical susceptibility as a function of Al concentration (0, 2, 3, 5 at.%). The films were characterized by X-ray diffractometer (XRD), EDAX 9100 analyser, atomic force microscopy (AFM) and third harmonic generation (THG). The Al (3 at.%) doped ZnO thin films exhibited the lower strain/stress than undoped films. The nonlinear properties of the ZnO:Al thin films have been found to be influenced by the films strain/stress.     

Effect of dimethyl sulfoxide on the electrical properties of PEDOT:PSS/n-Si heterojunction diodes

Effect of dimethyl sulfoxide (DMSO) on the electrical properties of PEDOT:PSS/n-Si heterojunction diodes has been studied. Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) was deposited on n-type Si wafer using facile process of spin coating. The DMSO content was varied from 0 to 8 vol%. Electrical characterization of these heterojunction diodes as performed using both current–voltage (I–V) and capacitance–voltage (C–V) measurements. All diodes showed rectifying behavior. AFM measurement revealed that the surface became more rough after the DMSO treatment of PEDOT:PSS films. The RMS values were found in the range of 4–6 nm. The resistivity of the PEDOT:PSS films decreased with increase in temperature. The addition of DMSO into PEDOT:PSS solution results in a decrease in resistivity of films by approximately two orders of magnitude. PEDOT:PSS films showed high transmission more than 85% in the entire visible region. Raman spectroscopy indicated effect of the DMSO treatment on the chemical structure of PEDOT chains, suggesting a conformational change of PEDOT chain in the film. An optimal value of DMSO was obtained with 5 vol% content, and it showed the best PEDOT:PSS films properties and good quality heterojunction diodes characteristics with ideality factor of 2.4 and barrier height 0.80 eV.     

Band offsets at ZnO/SiC heterojunction: Heterointerface in band alignment

Pulsed laser deposited ZnO layers on 6H-SiC substrates showed the six-fold symmetry, indicating a two-dimensional epitaxial growth mode. X-ray photoelectron spectroscopy was employed to study the valence band discontinuity and interface formation in the ZnO/6H-SiC heterojunction. The valence band offset was measured to be 1.38 ± 0.28 eV, leading to a conduction band offset value of 1.01 ± 0.28 eV. The resulting band lineup in epitaxial ZnO/6H-SiC heterojunction is determined to be of staggered-type alignment.     

Low-threshold pure UV electroluminescence from n-ZnO:Al/i-layer/n-GaN heterojunction

Ultraviolet (UV) electroluminescence (EL) of n-ZnO:Al (AZO)/i-layer/n-GaN heterojunctions with different intrinsic layers has been obtained. Rectifying behavior and EL spectra of the heterojunctions are investigated at room temperature. Under positive voltage, a dominant UV emission peak around ～370 nm is observed for both AZO/i-ZnO/n-GaN and AZO/i-MgO/n-GaN heterojunctions. Nevertheless, the UV emission peak intensity of AZO/i-MgO/n-GaN heterojunction is much stronger than that of AZO/i-ZnO/n-GaN heterojunction at the same voltage. The threshold voltage of AZO/i-MgO/n-GaN heterostructured device is as low as 2.3 V. The difference of EL spectra and the emission mechanism in these devices are discussed.     

Effect of ambient temperature on electrical properties of nanostructure n-ZnO/p-Si heterojunction diode

The nanostructure n-ZnO/p-Si heterojunction diode was fabricated by sol–gel method. The structural and morphological properties of the nanostructure ZnO film have been investigated. The X-ray diffraction spectra indicated that the films are of polycrystalline nature. The scanning electron microscopy images indicate that the surface morphology of ZnO film is almost homogeneous and the ZnO film is consisted of the circular formed with coming together of the nanoparticles. The electrical characterization of nanostructure n-ZnO/p-Si heterojunction diode has been investigated by current–voltage characteristics. The ideality factor (n) of the diode was found for different ambient temperatures and the obtained 6.40 value for 296 K is higher than unity due to the interface states between the two semiconductor materials and series resistance. The values of n increased with decreasing ambient temperature. The reverse current of the diode increased with illumination intensity of 100 mW cm⁻² and the diode gave a maximum open circuit voltage V_oc of 0.19 V and short-circuits current I_sc of 8.03 × 10⁻⁸ A.     

ZnO:Al薄膜中本征缺陷对光电效应的影响

在直流溅射法制备ZnO薄膜的过程中,通过合适选取溅射时氧氩的压力比,可以显著提高所得n-ZnO／p-Si异质结的光生短路电流,并且对该异质结的光生开路电压没有明显影响,从而可以用这种方法明显提高其光电转化能力。即使是在已经进行了n型掺杂的ZnO薄膜(这里为ZnO：Al)中,改变溅射时氧氩比对光电效应的影响也很明显。通过实验,已经证实了产生这种现象的原因是溅射时氧氩比的改变导致了ZnO薄膜内部的本征缺陷浓度的改变,使得载流子浓度变化而导致的结果。在氧氩压力比约为1：3时,光电转化效率最高。     

Al/ZnO/Al薄膜的结构与磁性分析

采用直流磁控溅射的方法制备了Al/ZnO/Al纳米薄膜,并对薄膜分别在真空及空气中进行退火处理.利用X射线衍射仪(XRD)和物理性能测量仪(PPMS)分别对薄膜样品的结构和磁性进行了表征.XRD分析表明,不同的退火氛围对薄膜的微结构有着很大的影响.采用了一种新的修正方法对磁测量结果进行修正,计算了基底拟合误差的最大值,并对修正后样品的磁性进行了分析.结果显示,室温铁磁性可能与Al和ZnO基体之间发生的电荷转移以及在不同退火氛围下Al在ZnO晶格中的地位变化有关. 关键词： Al/ZnO/Al薄膜 铁磁性 磁性表征     

Electroluminescence from ZnO nanowire-based p-GaN/n-ZnO heterojunction light-emitting diodes

Vertically aligned ZnO nanowires were successfully grown on the sapphire substrate by nanoparticle-assisted pulsed laser deposition (NAPLD), which were employed in fabricating the ZnO nanowire-based heterojunction structures. p-GaN/n-ZnO heterojunction light-emitting diodes (LEDs) with embedded ZnO nanowires were obtained by fabricating p-GaN:Mg film/ZnO nanowire/n-ZnO film structures. The current–voltage measurements showed a typical diode characteristic with a threshold voltage of about 2.5 V. Electroluminescence (EL) emission having the wavelength of about 380 nm was observed under forward bias in the heterojunction diodes and was intensified by increasing the applied voltage up to 30 V.