Preferential regrowth of indium–tin oxide (ITO) films deposited on GaN (0001) by rf-magnetron sputter

Effects of thermal treatments on the electrical properties and microstructures of indium–tin oxide (ITO)/GaN contacts have been investigated using a rf-magnetron sputter deposition followed by rapid thermal annealing. ITO films annealed at 800 °C revealed Schottky contact characteristics with a barrier height corresponding to ITO’s work function of 4.62 eV. The evolution of electrical properties of ITO/GaN contacts was attributed to the preferential regrowth of In₂O₃ (222)//GaN (0001) with an ideal metal–semiconductor Schottky contact. The feasible use of ITO/GaN as a transparent Schottky contact would be realized by the enhanced regrowth of In₂O₃ at high temperature. Received: 1 September 2000 / Accepted: 15 November 2000 / Published online: 28 February 2001     

Modification of the organic/La0.7Sr0.3MnO3 interface by in situ gas treatment

La_0.7Sr_0.3MnO₃ (LSMO) can act as a spin injection electrode in organic spin-valves and organic light-emitting devices. For the latter application, good control of the electronic structure of the organic/LSMO interface is a key issue to ensure sufficient current injection in the device. By exposing cleaned LSMO surfaces to activated oxygen and hydrogen, the work function of the samples can reach 5.15 and 4.3 eV, respectively, as shown by in situ photoemission measurements. The initial stage of formation of the organic/LSMO interface upon deposition of N,N′-bis-(1-naphyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) onto the oxygen-treated LSMO surface is examined. We find that the NPB molecules evenly cover the LSMO surface and that the interface barrier height is 0.8 eV, which is comparable to that at the NPB/indium tin oxide (ITO) interface with the ITO surface pretreated in situ by oxygen plasma.     

Ultraviolet photoelectron spectroscopy investigation of interface formation in an indium-tin oxide/fluorocarbon/organic semiconductor contact

It has been demonstrated that hole-injection in organic light-emitting devices (OLEDs) can be enhanced by inserting a UV-illuminated fluorocarbon (CF_x) layer between indium-tin oxide (ITO) and organic hole-transporting layer (HTL). In this work, the process of interface formation and electronic properties of the ITO/CF_x/HTL interface were investigated with ultraviolet photoelectron spectroscopy. It was found that UV-illuminated fluorocarbon layer decreases the hole-injection barrier from ITO to α-napthylphenylbiphenyl diamine (NPB). Energy level diagrams deduced from the ultraviolet photoelectron spectroscopy (UPS) spectra show that the hole-injection barrier in ITO/UV-treated CF_x/NPB is the smallest (0.46 eV), compared to that in the ITO/untreated CF_x/NPB (0.60 eV) and the standard ITO/NPB interface (0.68 eV). The improved current density-voltage (I-V) characteristics in the UV-treated CF_x-coated ITO contact are consistent with its smallest barrier height.     

Improvement of organic solar cells by flexible substrate and ITO surface treatments

In this paper, surface treatments on polyethylene terephthalate with polymeric hard coating (PET-HC) substrates are described. The effect of the contact angle on the treatment is first investigated. It has been observed that detergent is quite effective in removing organic contamination on the flexible PET-HC substrates. Next, using a DC-reactive magnetron sputter, indium tin oxide (ITO) thin films of 90 nm are grown on a substrate treated by detergent. Then, various ITO surface treatments are made for improving the performance of the finally developed organic solar cells with structure Al/P3HT:PCBM/PEDOT:PSS/ITO/PET. It is found that the parameters of the ITO including resistivity, carrier concentration, transmittance, surface morphology, and work function depended on the surface treatments and significantly influence the solar cell performance. With the optimal conditions for detergent treatment on flexible PET substrates, the ITO film with a resistivity of 5.6 × 10⁻⁴ Ω cm and average optical transmittance of 84.1% in the visible region are obtained. The optimal ITO surface treated by detergent for 5 min and then by UV ozone for 20 min exhibits the best WF value of 5.22 eV. This improves about 8.30% in the WF compared with that of the untreated ITO film. In the case of optimal treatment with the organic photovoltaic device, meanwhile, 36.6% enhancement in short circuit current density (J_sc) and 92.7% enhancement in conversion efficiency (η) over the untreated solar cell are obtained.     

Carrier transport mechanism in indium tin oxide (ITO)/silicon heterojunctions: effect of chlorine

Transparent-conducting-oxide (TCO)-based photovoltaic junctions have shown complexity in the transport phenomena at the interface. The present study is an attempt to understand the effect of chlorine at the interface between indium tin oxide (ITO) and Si. The ITO/Si junctions have been prepared by depositing transparent and conducting tin-doped indium oxide (ITO) thin films on as-cleaned and chlorine-treated single-crystal p-type and n-type silicon substrates using the reactive electron-beam evaporation technique. ITO/n-Si junctions have shown photovoltaic properties. The photoconversion efficiency of these junctions is observed to increase from 2.3% to 5.5% under chlorine treatment. The transport mechanism across these junctions has been studied by current–voltage (I–V , both dark and illuminated) and capacitance–voltage (C–V ) characterisation techniques. The carrier transport mechanism is found to be dominated by recombination at the depletion region for the junctions prepared with chlorine treatment, whereas for the other junctions, the thermionic process seems to be prominent. The unrealistic barrier heights observed in these junctions by the C–V technique confirms the complex nature of the interface. PACS 73.50.-h; 73.61.-r; 73.50.Pz; 73.40.-c     

在有机玻璃上射频溅射ITO组合薄膜

利用射频磁控溅射技术在有机玻璃表面上一次完成表面活化、ITO膜制备、SiO2 减反射膜制备过程。利用低能等离子体对有机玻璃表面进行改性以提高ITO膜的附着力。研究了氧分压等工艺参数对ITO膜导电性能及光学性能的影响。     

MoO_3作空穴注入层的有机电致发光器件(英文)

研究了三氧化钼(MoO3)薄层作为有机电致发光器件空穴注入层的器件性能和注入机制。发现1nm厚度下发光器件性能最佳,器件的最大电流效率比对比发光器件的最大电流效率提高1.6倍。器件的电容曲线表明MoO3薄层能有效提高空穴载流子的注入,多数载流子开始注入的拐点大约降低了9V。单空穴载流子电流曲线说明MoO3器件的电流注入是空间电荷受限电流注入机制,MoO3使阳极界面处形成欧姆接触,而对比器件的电流注入是陷阱电荷受限电流注入机制。器件的光伏曲线进一步说明器件性能的提高是由于MoO3层能使阳极界面能级分布发生改变,1nmMoO3厚度下器件的内建电势从对比器件的0.25V提高到了0.8V,有效降低了空穴注入势垒,提高了器件性能,但过厚的MoO3层由于增加了器件的串联内阻,会导致器件性能降低。     

Direct current and impedance spectroscopic studies on MoO3 modified ZnPc/ITO Schottky diodes

We use experimental results of direct current and low signal impedance spectroscopy to investigate the conduction mechanism in organic semiconductor ZnPc. The experimental results demonstrate an increase in current and holes mobility by the introduction of a thin MoO₃ film at the ITO/ZnPc interface. This significantly improves the device performance. The improvement is explained in terms of the reduction in the effective barrier for charge transfer from ZnPc to ITO.     

Enhanced resistance switching stability of transparent ITO/TiO2/ITO sandwiches

We report that fully transparent resistive random access memory(TRRAM) devices based on ITO/TiO2/ITO sandwich structure,which are prepared by the method of RF magnetron sputtering,exhibit excellent switching stability.In the visible region(400-800 nm in wavelength) the TRRAM device has a transmittance of more than 80%.The fabricated TRRAM device shows a bipolar resistance switching behaviour at low voltage,while the retention test and rewrite cycles of more than 300,000 indicate the enhancement of switching capability.The mechanism of resistance switching is further explained by the forming and rupture processes of the filament in the TiO 2 layer with the help of more oxygen vacancies which are provided by the transparent ITO electrodes.     

ITO界面调制层对GZO电极LED器件性能的影响

采用磁控溅射制备GZO和具有ITO界面调控层的GZO(ITO/GZO)透明导电薄膜作为大功率LED的电流扩散层,对比研究界面调控层对LED器件性能的影响。研究结果表明,ITO/GZO薄膜的透过率在可见光区达80%以上,退火后的ITO/GZO薄膜有较低的电阻率(1.15×10^-3 Ω·cm)。ITO调控层的介入能够调制GZO表面粗糙度,有利于改善LED外量子效率,降低GZO/p-GaN界面的接触势垒,提高LED器件的光电性 能。通过ITO界面调控后,LED器件20 mA驱动电流下的工作电压从9.5 V降低为6.8 V,发光强度从245 mcd 升到297 mcd,提高了20%;驱动电流为35 mA时,其发光强度从340.5 mcd 升到511 mcd,提高了50%。     

低压反应离子镀方法制备ITO透明导电膜

溅射镀膜方法是制备ITO透明导电膜最常用也是实验研究最多的方法。实验使用一种不同于溅射方法的另一种制备工艺—低压反应离子镀方法—制备ITO透明导电膜。实验对不同沉积速率和不同氧气流量对ITO透明导电膜的方块电阻以及光学透过率的影响进行了详细地分析,并综合比较得到了当沉积速率为0.5nm/s,氧气流量为24cm3/min时,在波长为550nm处,方块电阻为20Ω,λ=550nm透过率为90.8%的优质ITO透明导电膜。     

Structural and electronic implications for carrier injection into organic semiconductors

We report on the structural and electronic interface formation between ITO (indium-tin-oxide) and prototypical organic small molecular semiconductors, i.e., CuPc (copper phthalocyanine) and α-NPD (N,N′-di(naphtalen-1-yl)-N,N′-diphenyl-benzidine). In particular, the effects of in situ oxygen plasma pretreatment of the ITO surface on interface properties are examined in detail: Organic layer-thickness dependent Kelvin probe measurements revealed a good alignment of the ITO work function and the highest occupied electronic level of the organic material in all samples. In contrast, the electrical properties of hole-only and bipolar organic diodes depend strongly on the treatment of ITO prior to organic deposition. This dependence is more pronounced for diodes made of polycrystalline CuPc than for those of amorphous α-NPD layers. X-ray diffraction and atomic force microscopic (AFM) investigations of CuPc nucleation and growth evidenced a more pronounced texture of the polycrystalline film structure on the ITO substrate that was oxygen plasma treated prior to organic layer deposition. These findings suggest that the anisotropic electrical properties of CuPc crystallites, and their orientation with respect to the substrate, strongly affect the charge carrier injection and transport properties at the anode interface.     

Progress in Modification of Indium-Tin Oxide/Organic Interfaces for Organic Light-Emitting Diodes

The oxide/organic interfaces play crucial roles in the hole injection from the anode electrodes to the emitting organics in organic light-emitting diodes (OLEDs), and hence have strong impacts on the efficiencies and other properties of the devices. Indium-tin oxide (ITO) is currently the most popular anode material used in OLEDs due to several merits, such as good etch ability, good adherence, high transparency, low resistivity, and high work function. Interfacial engineering between the ITO electrode and the overlying organic layers is an important process to obtain the high performance of the diode devices. In this article, recent progress in modification of the ITO/organic interfaces is reviewed, as these interfaces are important to the development of the technologies aiming at improving the electroluminescence, and efficiencies as well as reducing the operation voltages of OLEDs. ITO/Organic interfacial properties can be controlled or modified by simply changing the surface properties of ITO using chemical or physical treatments, and by adding a buffer layer (e.g., metal, oxide, or organic thin films) between the ITO and hole transport or emitting organic layers. The literature data showed that the electroluminescence, efficiencies, and lifetimes of the OLEDs could be greatly increased and the operation voltage considerably decreased when the ITO/organic interfaces have been properly improved.     

Synthesis and characterization of p-GaSe thin films and the analyses of I–V and C–V measurements of p-GaSe/p-Si heterojunction under electron irradiation

Gallium Selenide (GaSe) thin films were grown by the electrochemical deposition (ECD) technique on Indium tin oxide (ITO) and p-Si (100) substrates. The Electron paramagnetic resonance (EPR) spectrum of GaSe thin films’ growth on ITO was recorded at room temperature. According to EPR results, the g value of an EPR signal obtained for GaSe deposited on ITO is 2.0012?±?0.0005. In/GaSe/p-Si heterojunction was irradiated with high-energy (6?MeV) and low-dose (1.53?×?10¹⁰?e^??cm^?2) electrons. The ideality factor of the In/GaSe/p-Si device was calculated as 1.24 and barrier height was determined as 0.82?eV from I–V measurements before irradiation. Acceptor concentration, built-in potential and barrier height of the In/GaSe/p-Si device were also obtained as 0.72?×?10^14?cm^?3, 0.65?eV and 0.97?eV from C–V measurements, respectively. After irradiation, the ideality factor n and barrier height Φ_b values of the In/GaSe/p-Si device were calculated as 1.55 and 0.781?eV, respectively. Acceptor concentration, the built-in potential and barrier height values of the In/GaSe/p-Si device have also shown a decrease after 6?MeV electron irradiation. This change in heterojunction device parameters shows that current transport does not obey thermionic emission, and thus tunneling could be active due to the defects formed by irradiation at the In–GaSe interface.     

Ca/Ag bilayer cathode for transparent white organic light-emitting devices

We have demonstrated that the compositional modification of the Ca/Ag films is principally responsible for a high transmittance (over 70% in the visible range) and low sheet resistance (10-12 Ω/sq). X-ray photoelectron spectroscopy (XPS) sputter depth profiling of Ca/Ag structure reveals the presence of Ca(OH)₂ and Ca metal. A chemical model of the Ca/Ag cathode is proposed. Using transparent ITO anode and Ca (10 nm)/Ag (10 nm) cathode, efficient white organic light-emitting devices (WOLEDs) emitting from both sides have been fabricated. Brightness of 3813 cd/m² and Commission Internationale de l’Eclairage (CIE) coordinates (0.36, 0.34) at 10 V through ITO anode and values of 1216 cd/m² and (0.33, 0.30) through Ca/Ag cathode are reported. A low turn-on voltage of 5.5 V is measured.     

大尺寸0.55mm ITO透明导电膜玻璃的翘曲度

ITO透明导电膜玻璃的翘曲度是评价大尺寸薄基片ITO玻璃的重要指标之一。利用磁控射频溅射技术制备了ITO薄膜。研究了基片加热前、后的翘曲度和ITO膜层应力对ITO玻璃翘曲度的影响以及ITO成膜温度分布对ITO玻璃翘曲度的影响。结果表明,薄基片ITO玻璃的翘曲度主要是在镀膜时ITO膜层压应力大引起的,选择合适的成膜温度分布可明显减小ITO玻璃的翘曲度。     

电极处势垒对新结构器件电子输运的影响

在新结构薄膜电致发光器件中,电极处的势垒的高度决定电子的注入数量.在电极界面处插入不同的薄膜材料,可以改变势垒的高度,并对电子注入数量和器件的发光亮度产生影响.通过拟合计算得到ZnO/SiO,ITO/SiO的界面势垒高度分别为0.51和1.87eV. 关键词：     

有机层界面对双层有机发光二极管复合效率的影响

建立了双层有机发光二极管中载流子在有机层界面复合的无序跳跃理论模型.由于有机分子材料的空间及能带结构的无序性，采用刚体模型处理有机层界面问题是不恰当的，而采用无序跳跃模型比较合理.复合效率及复合电流由载流子跳跃距离、有机层界面的有效势垒高度及该界面处的电场强度分布所决定：在双层器件ITO/α-NPD/Alq₃/Al中，当所加电压小于19.5V时，复合效率随着载流子跳跃距离的增加而增加，而大于19.5V时，复合效率随着其距离的增加而减少；复合效率随着有机层界面有效势垒高度的增加而增加； 关键词： 有机层界面 双层有机发光二极管 复合效率 有效势垒高度 无序跳跃模型     

Growth mode and interface structure of Ag on the HF-treated Si(111):H surface

A growth mode and interface structure analysis has been performed for Ag deposited at a high temperature of 300°C on the HF-treated Si(111):H surface by means of medium-energy ion scattering and elastic recoil detection analysis of hydrogen. The measurements show that Ag grows in the Volmer-Weber mode and that the Ag islands on the surface are epitaxial with respect to the substrate. The preferential azimuthal orientation is A-type only when Ag is deposited slowly. The interface does not reconstruct to the √3 × √3-Ag structure, which is normally observed for Ag deposition above 200°C on the Si(111)7 × 7 surface, but retain bulk-like structure. The presence of hydrogen at the interface is demonstrated after deposition of thick (1100 Å) Ag films. However, the amount of hydrogen at the interface is not a full monolayer. This partial desorption of hydrogen from the interface explains why the Schottky barrier heights of Ag/Si(111):H diodes are close to those of Ag/Si(111)7 × 7 and Ag/Si(111)2 × 1.     

用光伏效应研究有机薄膜电致发光器件中的接触性质

首次发现了有机薄膜电致发光器件的光生伏特效应，通过对器件的光电流响应谱的详细研究，分析了不同结构的有机发光器件中的有机半导体之间，以及有机半导体与电极材料之间的半导体接触性质，发现有机发光材料Ａｌｑ３，有机空穴传输材料ｄａｉｍｉｎｅ与金属铝电极之间形成阻挡接触，是电致发光器件发光和产生光电效应的根本原因；而双层器件中有机层Ａｌｑ３与ｄｉａｍｉｎｅ之间的结是双层器件产生高发光效率的原因，正是这种结在双层器件中起了局限载流子和激子的作用，使发光亮度大为提高，结合分区掺杂实验结果，给出了较完善的能带模型．