Hydrothermal fabrication of p-Cu2O−n-ZnO films and their properties for photodegradation and ultraviolet sensors

This article reports spin coating and hydrothermal approaches to the synthesis of Cu₂O seed layer−ZnO and Cu₂O film−ZnO heterojunction films on fluorine-doped tin oxide substrates. Cu₂O seed layers and an ethylene glycol (EG) reducing agent were employed to obtain pure, uniform, and adhesive Cu₂O films on the substrate. Transmission electron microscopy validated the heterojunctions with clear interfaces between each component on the p-Cu₂O film−n-ZnO (with EG) sample, the conductive types of which were determined through Mott−Schottky measurements. Constructed energy band diagrams supported the Mott−Schottky result, manifesting favorable conduction band positions for the generation of •O₂⁻ radicals for all constituent materials and indicating smooth charge carrier transport for the p-Cu₂O film−n-ZnO (with EG) sample. Furthermore, abundant p−n junction interfaces synergistically enabled the sample to exhibit the most satisfactory photodegradation capability (rate constant ≈ 8.9 × 10⁻³ min⁻¹), which was attributable to the predominance of •OH radicals. The sample's rectifying (diode) behavior with a ratio of the current density (J) at +3 V (forward bias) to that at −3 V (reverse bias) of approximately 27 was observed without ultraviolet illumination. Moreover, the J at −3 V is under illumination approximately 80 times that without illumination, implying the suitability of the sample for UV detectability.     

MgO界面层对n-ZnO纳米棒/p-GaN异质结LED光电性能的影响

为了较好地实现n-ZnO的电致发光(EL),利用水热法在p-GaN外延片上制备了ZnO纳米棒阵列,构造了n-ZnO纳米棒/p-GaN异质结LED原型器件,并研究了MgO界面层对器件光电性能的影响。结果表明,n-ZnO纳米棒/p-GaN异质结器件具有明显的二极管整流效应。室温、正向偏压下,n-ZnO纳米棒/p-GaN异质结LED仅在430nm附近具有单一的发光峰,而n-ZnO纳米棒/MgO/p-GaN异质结LED的电致发光光谱由一个从近紫外到蓝绿光区的宽发光带组成。结合光致发光(PL)谱和Anderson能带模型,深入分析了n-ZnO纳米棒/p-GaN异质结的载流子复合机制。     

Structural and functional properties of ZnO thin films grown on Si substrates by air assisted USP method from non-aqueous solutions at low-temperature

In this work, we deals with the processing and characterization of transparent conducting ZnO thin films on p-type Silicon substrates (1 0 0) by air assisted Ultrasonic Spray Pyrolysis (USP) method. The thin films from different Zn acetate precursor solution concentrations (0.1, 0.2, 0.3 and 0.4 M) were deposited at several temperatures (400, 450 and 500 °C) with thickness from ～100 to ～500 nm. The effects of precursor solution concentration, deposition time and temperature on the structural, morphological, optical, and electrical properties of ZnO films were studied by X-ray Diffraction (XRD), Atomic Force Microscopy (AFM), UV–Vis-NIR spectroscopy, and Hall Effect techniques, respectively. It has been shown that on the ZnO film surface, the preferred orientation, the average crystallite size, the electrical resistivity and the RMS surface roughness depend on the substrate temperature. The grown films have showed a good adhesion and an excellent optical transmission of about 80–95% within the visible range (400–800 nm) and a direct band gap from 3.35 to 3.23 eV with the increase of the substrate temperature and the deposition time. All the PL spectra have exhibited a typical green-yellow emission band. Additionally photovoltaic (PV) activities of n-ZnO/p-Si heterostructures fabricated are investigated.     

Preparation, characterization and activity evaluation of p–n junction photocatalyst p-CaFe2O4/n-ZnO

p–n junction photocatalyst p-CaFe₂O₄/n-ZnO was prepared by ball milling of ZnO in H₂O doped with p-type CaFe₂O₄. The structural and optical properties of the p–n junction photocatalyst p-CaFe₂O₄/n-ZnO were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–vis diffuse reflection spectrum (DRS) and fluorescence emission spectra. The photocatalytic activity of the photocatalyst was evaluated by photocatalytic degradation of methylene blue (MB). The results showed that the photocatalytic activity of the p-CaFe₂O₄/n-ZnO was higher than that of ZnO. When the amounts of doped p-CaFe₂O₄ were 0.0 wt.% and 1.0 wt.%, the photocatalytic degradation efficiencies were 50.1 and 73.4%, respectively. Effect of ball milling time on the photocatalytic activity of the photocatalyst was also investigated. The mechanisms of influence on the photocatalytic activity were also discussed by the p–n junction principle.     

Fabrication of p-type CuSCN/n-type micro-structured ZnO heterojunction structures

Micro-sized ZnO rods on a SnO₂ coated glass substrate were obtained by the spray pyrolysis method. Then a p-type CuSCN layer was deposited on this micro-sized n-ZnO to produce a p-n heterojunction. Temperature dependent current-voltage characteristics were measured in the temperature range 150-300 K with a step of 25 K. The current-voltage characteristics exhibit electrical rectification behavior. The zero bias barrier height Φ_b0 increases and the ideality factor n decreases with an increase in temperature. The apparent Richardson constant and mean barrier height were found to be 0.0028 A cm^− 2 K^− 2 and 0.228 eV respectively in the range 150-300 K. After a barrier height inhomogeneity correction, the Richardson constant and the mean barrier height were obtained as 65.20 A cm^− 2 K^− 2 and 0.840 eV, respectively.     

Effect of electrodeposition and annealing of ZnO on optical and photovoltaic properties of the p-Cu2O/n-ZnO solar cells

Cu₂O/ZnO p–n heterojunction solar cells were fabricated by rf sputtering deposition of n-ZnO layer, followed by electrodeposition of p-Cu₂O layer. The different electrodeposition potentials were applied to deposit Cu₂O on ZnO. The particle size, crystal faces, crystallinity of Cu₂O is important factor which determine the p–n junction interface and consequently their effect on the performance of the heterojunction solar cell. It is observed that at −0.6 V, p-Cu₂O film generates fewer surface states in the interband region due to the termination of [1 1 0] resulting in higher efficiency (0.24%) with maximum particle size (53 nm). The bandgap of Cu₂O at this potential is found to be 2.17 eV. Furthermore, annealing of ZnO film was performed to get rid of deteriorating one and two dimensional defects, which always reduce the performance of solar cell significantly. We found that the solar cell performance efficiency is nearly doubled by increasing the annealing temperature of ZnO thin films due to increasing electrical conductance and electron mobility. Doping studies and fine tuning of the junction morphology will be necessary to further improve the performance of Cu₂O/ZnO heterojunction solar cells.     

n-ZnO/p-Si紫外至近红外增强型广谱光探测器

采用直流反应溅射法,在一定的溅射功率和衬底温度等条件下控制气体组分,优选Ar:O2＝8:1成功研制出高响应度n-ZnO/p-Si紫外至近红外增强型广谱光探测器.实验关键是利用缺O法在n-ZnO薄膜内有效引入O缺位Vo,而Vo可增强紫蓝波段的光响应.测试结果显示,ZnO薄膜的光致发光(PL)谱除在388 nm处存在紫外带边发射主峰外,还在416 nm处出现由O缺位导致的发射峰;X射线衍射(XRD)谱表明,薄膜中的晶体为高c轴取向的纤锌矿结构;n-ZnO/p-Si光探测器在光照时I-V特性显示,光电流随反向偏压的增加迅速上升;在5 V的反向偏压下,紫外区(310～388 nm)的光响应高达0.75～1.38 A/W,紫蓝光区(400～430 nm)的光响应大大增强,400～800 nm波段的光谱响应稳定在0.90 A/W.