利用湿法腐蚀提高红光LED外延片的发光效率

采用熔融态的KOH对AlGaInP基红光LED外延片进行了表面粗化处理。研究了粗化温度、粗化时间对LED外延片表面形貌的影响,并利用原子力显微镜(AFM)、半导体芯片自动测试系统对LED器件的相关性能(形貌、I-V特性曲线、亮度和主波长)进行了表征。比较了粗化前后的LED亮度和电流特性变化。测试结果表明:利用熔融态的KOH对AlGaInP基红光LED外延片进行表面粗化可以有效地抑制光在通过LED表面与空气接触界面时产生的全反射,得到性能更好的器件。实验结果显示,采用熔融态KOH,在粗化温度为200℃、粗化时间为8min时,能使制作的红光LED外延片发光效率提高30%。     

薄膜AlGaInP发光二极管中不同反光镜的研究

本文计算了GaP/Au 反光镜, GaP/SiO2/Au 三层ODR and GaP/ITO/Au 三层ODR的反射率随角度的变化值。制作了GaAs衬底的AlGaInP LED,Au反光镜、SiO2 ODR和ITO ODR的薄膜AlGaInP LED。在20mA下,四种样品光输出功率分别为1.04mW, 1.14mW, 2.53mW and 2.15mW。制作工艺退火后,Au扩散使Au/GaP反光镜的反射率降至9％。1/4波长的ITO和SiO2透射率不同造成了两种薄膜LED光输出功率不同。ITO ODR中加入Zn可以大大降低LED的电压,但并不影响LED的光输出。     

ITO掩膜干法粗化GaP提高红光LED的提取效率

采用氧化铟锡(ITO)颗粒掩膜,经感应耦合等离子体(ICP)刻蚀后制作了表面粗化的红光发光二极管(LED),并且研究了ITO腐蚀时间对粗化表面形貌的影响。测试结果表明,当粗化颗粒的大小为200～500 nm、腐蚀深度约200～400 nm时,能使制作的表面粗化红光LED在20 mA注入电流下光提取效率提高30%以上。并且,表面粗化不会影响LED的发光强度角度分布。     

衬底温度对ITO/Ga2O3深紫外透明导电薄膜性能的影响

用磁控溅射的方法在石英玻璃上制备了ITO/Ga₂O₃双层膜。用X射线衍射仪、扫描电镜、双光束分光光度计和霍尔效应测试仪研究了衬底温度对ITO/Ga₂O₃双层膜的结构、表面形貌、光学性能和电学性能的影响。双层膜结构受衬底温度的影响,当衬底温度从100C 升高到 350C时,薄膜的电阻率由6.71′10^-3 Ω.cm 降到 1.91′10^-3 Ω.cm。衬底温度300C制备的ITO(22nm)/Ga₂O₃(50nm)双层膜的面电阻为373.3Ω,在300nm波长的深紫外透过率为78.97%。     

具有纳米级结构出光面的AlGaInP基发光二极管

研究了一种利用金属自组装纳米掩膜和ICP刻蚀对AlGaInP基发光二极管(LED)表面进行粗化的技术,使光输出得到了提高.粗化了的AlGaInP基LED比常规的AlGaInP基LED,光强提高了27%,光功率提高了12.6%,实验结果具有可重复性.可以进一步优化Au颗粒的周期和分散程度,提高AlGaInP基LED的提取效率.     

薄膜AlGaInP发光二极管中光子吸收的研究

分析了薄膜发光二极管中光子的路径,对比了AlGaInP薄膜发光二极管的反光镜有无AlGaInP层的反射率,分析了AlGaInP层的吸收并计算了光提取效率。制作了不同GaP厚度的TF AlGaInP LED。在20mA的驱动电流下,0.6μm GaP的LED比8μm GaP 的LED光输出功率高33％。提出了在0.6μm GaP的LED中腐蚀去除非欧姆接触点处的重掺GaP。在n型电极和p型欧姆接触点间的电流扩展的设计和优化需要更进一步的研究。     

快速热退火对真空蒸镀ITO InGaN/GaN蓝光LED的影响

制作了8milX 10mil的InGaN/GaN 蓝光LED(λ=460nm),采用了真空蒸镀在P-GaN上淀积了240nm的ITO。对不同温度下(100℃至550℃)热退火ITO的电学特性和光学特性进行了比较分析。实验发现,450℃下热退火ITO电阻率低至1.19X10_-4Ω?cm,而此温度下得到高透射率94.17%。在20mA注入电流下,正向电压和输出功率分别为3.14V and 12.57mW。另外,550℃ITO退火下制备的LED光通量最大,为0.49lm,这是因为此温度下透射率较大。     

ITO薄膜的电阻并联效应研究

采用电子束蒸发镀膜方法在K9玻璃基底上分别镀制了ITO/SiO₂/ITO,ITO/Ti₂O₃/ITO和ITO/MgF₂/ITO结构的多层薄膜,用四探针方块电阻仪测量薄膜表面的方块电阻,用原子力显微镜观测样品的表面微观形貌。结果显示,当ITO薄膜的粗糙度较大且介质薄膜的物理厚度小于100nm时,各层ITO薄膜之间通过山峰状的凸起结构相连通,导致样片表面的方块电阻测量值与各层ITO薄膜电阻的并联值相当。这表明,当ITO薄膜的粗糙度较大且介质薄膜厚度较小时,各层ITO薄膜表现出电阻并联效应。利用多层ITO薄膜的电阻并联效应设计并制备了450～1200nm超宽光谱透明导电薄膜,用四探针方块电阻仪测量了试验样片的表面方块电阻,用紫外-可见-近红外分光光度计测试了样片的光谱透射率。结果显示,在相同表面方块电阻条件下,相比于单层ITO薄膜,利用ITO薄膜电阻并联效应所制备的多层透明导电薄膜具有更高的光谱透射率。     

新型红光LED中ITO的特性研究

用真空电子束蒸镀的方法制备半导体发光二极管LED 所用的ITO(indium tin oxide)膜。利用TLM(transmission line model)研究ITO与GaP接触特性。在氮气环境,435℃条件下,快速热退火40s能获得最小的接触电阻4.3×10-3Ωcm2。Hall测试和俄偈电子能谱表明,影响接触电阻的主要原因是ITO载流子浓度的改变和In,Ga,O的扩散。另外,制作了以300nm ITO为窗口层的新型AlGaInP红光LED并研究其可靠性。发现ITO的退化导致了LED的电压持续升高。而ITO与GaP热膨胀系数的不同导致了LED的最终失效。     

聚苯乙烯球掩膜干法粗化提高LED发光效率

采用聚苯乙烯球作为掩膜层,对ITO(氧化铟锡)薄膜进行干法蚀刻实现ITO表面的粗化,提高GaN基大功率LED芯片外量子效率。利用AFM及SEM对ITO表面进行表征,比较了微球尺寸对ITO表面形貌及芯片光电参数的影响。结果表明,ITO表面经过350nm聚苯乙烯球图形化后,在未影响芯片正向电压和波长的前提下所制备的1mm×1mm波长为457nm的大功率LED芯片,亮度增加可达30%以上。     

A Ga-doped ZnO transparent conduct layer for GaN-based LEDs

An 8 μm thick Ga-doped ZnO (GZO) film grown by metal-source vapor phase epitaxy was deposited on a GaN-based light-emitting diode (LED) to substitute for the conventional ITO as a transparent conduct layer (TCL). Electroluminescence spectra exhibited that the intensity value of LED emission with a GZO TCL is markedly improved by 23.6% as compared to an LED with an ITO TCL at 20 mA. In addition, the forward voltage of the LED with a GZO TCL at 20 mA is higher than that of the conventional LED. To investigate the reason for the increase of the forward voltage, X-ray photoelectron spectroscopy was performed to analyze the interface properties of the GZO/p-GaN heterojunction. The large valence band offset (2.24±0.21 eV) resulting from the formation of Ga2O3 in the GZO/p-GaN interface was attributed to the increase of the forward voltage.     

Properties of the ITO layer in a novel red light-emitting diode

An optically transparent electrode, indium tin oxide (ITO) film is fabricated by vacuum E-beam evaporation. The thermal annealing effects on the ITO/GaP contact have been investigated by means of the transmission line model method. Under 435℃, with rapid thermal annealing for 40 s in N2 ambient, the ITO contact resistance reaches the minimized value of 4.3 × 10-3 Ω·cm2 . The results from Hall testing and Auger spectra analysis indicate that the main reasons for the change of the contact resistance are the difference in the concentration of carriers and the diffusion of In, Ga, O. Furthermore, the reliability of AlGaInP LEDs with a 300-nm thickness transparent conducting ITO film is studied. The increase of LED chip voltage results from the degradation of ITO film. Moreover the difference between the thermal expansion coefficient of GaP and ITO results in the invalidation of the LED chip.     

On an AlGaInP-Based Light-Emitting Diode With an ITO Direct Ohmic Contact Structure

An interesting AlGaInP multiple-quantum-well light-emitting diode (LED) with a direct ohmic contact structure, formed by an indium–tin–oxide (ITO) transparent film and AuBe diffused thin layer, is fabricated and studied. The direct ohmic contact structure is performed by the deposition of an AuBe diffused thin layer and the following activation process on the surface of a Mg-doped GaP window layer. Experimental results demonstrate that a dynamic resistance of 5.7 $Omega$ and a forward voltage of 1.91 V, under an injection current of 20 mA, are obtained. In addition, the studied LED exhibits a higher external quantum efficiency of 9.7% and a larger maximum light-output power of 26.6 mW. The external quantum efficiency is increased by 26% under the injection current of 100 mA, as compared with the conventional LED without this structure. This is mainly attributed to the reduced series resistance resulted from the relatively uniform distribution of AuBe atoms near the GaP layer surface and the effective current spreading ability by the use of ITO film. Moreover, the life behavior of the studied LED, under a 20-mA operation condition, is comparable to the conventional LED without this structure.      

Characteristics of an AlGaInP-Based Light Emitting Diode With an Indium-Tin-Oxide (ITO) Direct Ohmic Contact Structure

An AlGaInP multi-quantum-well (MQW) light-emitting diode (LED) with a direct Ohmic contact structure, formed by an indium-tin-oxide (ITO) transparent film and AuBe diffused thin layer, is fabricated and studied. By the deposition of an AuBe metallic thin layer on the surface of Mg-doped GaP window layer, followed by a thermal activation process, a direct Ohmic contact between ITO and p-GaP layers can be obtained. Experimentally, under an injection current of 20 mA, a dynamic resistance of 5.7 $Omega$ and a forward voltage of 1.91 V, are obtained. In addition, a higher external quantum efficiency of 9.7% and a larger maximum light output power of 26.6 mW are found for the studied LED. As compared with the conventional LED without this structure, the external quantum efficiency of the studied device is increased by 26% under the injection current of 100 mA. This is mainly attributed to the reduced series resistance resulted from the relatively uniform distribution of AuBe atoms near the GaP layer surface and the effective current spreading ability by the use of ITO film. Moreover, the life behavior is not degraded by using this AuBe diffused layer for the studied LED under a 20 mA operation condition.      

Growth and properties of VPE GaP for green LEDs

The PH₃-HCl-Ga-H₂ technique for VPE growth of GaP is described. The influence of various growth parameters, including substrate temperature, orientation, and PH₃ flow rate on morphology and growth rate are described. For both VPE and LPE nitrogen doping is known to be a major factor in obtaining high green luminescence efficiency. The major emphasis of this paper is an examination of the effect of nitrogen concentration in the range less than 10¹⁹ cm⁻³ (using the Lightowlers correction factor) on the growth process and materials properties, such as defect structure, photoluminescence spectra (at 300 and 77K) and photoluminescence intensity and lifetime. The LED device performance (B/J and efficiency) is used as the final test of material quality. Nitrogen is found to be incorporated far in excess of the solubility limit, and the solid gas distribution coefficient for nitrogen is found to increase rapidly with decreasing temperature below 840°C . The optimum nitrogen concentration for high diode efficacy, photoluminescence intensity, and lifetime is found to be approximately 5 × 10¹⁸ cm⁻³, where diodes fabricated by Zn diffusion into the VPE GaP have efficiencies at a current density of 10 A/cm² of 0.1%, comparable to the state-of-the-art in the more widely used grown p-n junctions using LPE.     

Improvement of the contact resistance between ITO and pentacene using various metal-oxide interlayers

Ultra-thin Al₂O₃, Ta₂O₅, and TiO₂ films were deposited on the indium tin oxide (ITO) surfaces in organic thin film transistors using the atomic layer deposition (ALD) process at room temperature, and the contact resistance was significantly improved with the increase of the dielectric constant of the interlayer. The electronic band diagrams of the pentacene/ITO structures after ALD treatment on ITO surface with various metal-oxides were measured using in situ ultra-violet photoelectron spectroscopy during the step-by-step deposition of pentacene, and these results explained the decrease of the hole injection barriers and the resulting improvement of the contact resistance between pentacene/ITO interface.     

The role of molybdenum oxide as anode interfacial modification in the improvement of efficiency and stability in organic light-emitting diodes

It has been experimentally found that molybdenum oxide (MoO₃) as the interfacial modification layer on indium-tin-oxide (ITO) in organic light-emitting diodes (OLEDs) significantly improves the efficiency and lifetime. In this paper, the role of MoO₃ and MoO₃ doped N,N′-di(naphthalene-1-yl)–N,N′-diphenyl-benzidine (NPB) as the interface modification layer on ITO in improvement of the efficiency and stability of OLEDs is investigated in detail by atomic force microscopy (AFM), polarized optical microscopy, transmission spectra, ultraviolet photoemission spectroscopy (UPS) and X-ray photoemission spectroscopy (XPS). The studies on the energy level and the morphology of the films treated at different temperatures clearly show that the MoO₃ and MoO₃:NPB on ITO can reduce the hole injection barrier, improve the interfacial stability and suppress the crystallization of hole-transporting NPB, leading to a higher efficiency and longer lifetime of OLEDs.