二维光子晶体LED专利技术分析

LED是一种能够将电能转化为可见光的固态的半导体器件,目前LED已在科研和生产领域取得了广泛的应用。光子晶体是由周期性排列的不同折射率的介质制造的规则光学结构,其中二维光子晶体能使更多方向上的平面光衍射出LED表面,因此目前主要用二维光子晶体来提高LED的出光效率。本文总结了与二维光子晶体LED相关的国内和国外专利的申请趋势、主要申请人分布以及重点技术的发展路线进行了梳理。     

利用常规工艺提高光子晶体GaN LED的出光效率

计算了GaN二维光子晶体的能带结构,并利用常规工艺在国内首次制备出了GaN基二维平板结构的光子晶体蓝光LED。经过器件测试表明,与没有制作光子晶体的器件相比,光子晶体使器件的有效出光效率达到了原来的1.5倍以上。另外,还对感应耦合等离子体刻蚀(ICP)的制备光子晶体LED的刻蚀工艺进行了分析。     

光子晶体提高GaN基LED出光效率的研究进展

光子晶体作为有效提高LED出光效率的手段之一,在过去的十多年受到了广泛的关注.简述了光子晶体提高LED出光效率的物理原理.从GaN基LED不同光子晶体的结构、晶格常数和高度等参数的影响出发,通过几种新型光子晶体发光二级管的介绍,总结了近年来利用光子晶体提高LED出光效率所取得的研究进展.     

高出光率GaN基光子晶体LED的研究进展

在LED上制作光子晶体结构将会提高LED的出光效率,这使得LED应用范围更广.主要从不同的光子晶体加工工艺出发,总结近年来GaN基光子晶体LED的研究进展,介绍新的工艺和实验结果.通过比较发现,利用光子晶体的光子禁带效应和光栅衍射原理,都能够提高LED的出光效率,但需要和光子晶体的结构参数以及相应的加工工艺相结合,使出光效率和光场能流密度有大幅度的提高,从而实现LED出光效率的提高,使LED取代白炽灯等光源应用于生活照明成为可能.     

蓝色LED发光效率提高50%

松下电器产业日前开发成功了发光效率达原来1.5倍的GaN蓝色发光二极管(LED)芯片。该产品是通过在蓝色LED芯片表面大量设置直径约1μm、高约0.5μm的圆柱状凹凸而实现的。芯片内部产生的蓝色光,可将30%左右的光线照射到芯片外部。今后通过改进蓝色LED芯片,预计将能够照射出60%左右的光。此次开发的蓝色LED芯片,利用光子晶体的特性,提高了发光效率。光子晶体是指其内部具有周期性折射率分布的晶体,配置2种折射率差异较大的介质。照射到光子晶体中的光线会因其周期性折射率分布而使光线发生衍射。由于这种效应,从芯片内部照射到芯片外部…     

含正负材料的一维光子晶体的光学特性研究

为了得到新的传输性质,把具有负介电常数和磁导率的负折射率材料引入到光子晶体当中,运用Maxwell电磁波方程和Bloch理论得到的含正负折射率材料的色散关系的解析式,分别分析一维无限周期且正折射率材料和负折射率材料交替组成的一维光子晶体的禁带结构和色散特性,并与常规的正折射率材料的光子晶体比较,发现含正、负折射率材料且呈周期性重复的双层结构的复合光子晶体其光子具有较宽禁带,为设计超宽禁带的光子带隙结构提供了一定的理论可能性。     

侧面粗化提高GaN基LED出光效率研究

通过对传统结构LED出光分析,提出采用侧面粗化来提高GaN基LED出光效率的方法,使用蒙特卡罗光子追踪方法对器件出光效率进行了模拟。结果表明:粗化侧面为三角状、底角为55°时出光效率最高,随机粗化可以获得比固定角度粗化更高的出光效率,同时降低材料的吸收系数可以提高LED的出光效率,在吸收系数为10/cm时,经过粗化后的LED出光效率可以达到46.1%。模拟结果证明侧面粗化可以较大地提高LED的出光效率。     

折射率匹配对绿光发光二极管微显示光学性能影响

设计了用于发光二极管(LED)微显示器折射率匹配层结构,可以提高LED微显示器的光学性能。倒装结构的LED微显示器出光面为蓝宝石(折射率约1.76),它和空气的折射率(约为1.0)相差较大,会有很大一部分光因为全反射而反射回器件内部被吸收,导致器件的光效率降低。本文通过涂敷折射率匹配层硅胶(折射率约1.41～1.53)的方法,改变器件表层的折射率使其和空气的折射率相匹配,增加光逃逸锥角,从而提高器件的光效率。结果表明涂敷硅胶可以提高光效率约25.75%,在涂敷硅胶基础上盖玻璃片(折射率约1.47)可提高光效率约32.78%,且硅胶涂敷前后器件的电学、光学、结温稳定性好。尽管增加的是侧方向的光通量,但是其光效率的增加为高效率LED微显示的实现提供了参考依据。     

利用光子晶体提高InP基LED出光效率

应用FDTD方法计算了二维无限大光子晶体的能带结构,并制备出了InP基二维平板结构的光子晶体器件.在制备过程中尝试了仅用PMMA做掩模以及PMMA和SiO2做掩模两种方法.结果表明,不使用SiO2做掩模的情况下,由于PMMA胶选择性较差,在刻蚀过程中难以保证图形的准确转移.而增加SiO2掩模后,获得了图形质量良好的光子晶体结构.成功实现了利用光子晶体结构增强LED的出光效率,与未制作光子晶体结构的LED相比,光子晶体结构LED的出光效率可在原来基础上提高1倍以上.并且随着晶格常数的增加,出光效率进一步提高.     

利用光子晶体提高InP基LED出光效率

应用FDTD方法计算了二维无限大光子晶体的能带结构,并制备出了InP基二维平板结构的光子晶体器件.在制备过程中尝试了仅用PMMA做掩模以及PMMA和SiO2做掩模两种方法.结果表明,不使用SiO2做掩模的情况下,由于PMMA胶选择性较差,在刻蚀过程中难以保证图形的准确转移.而增加SiO2掩模后,获得了图形质量良好的光子晶体结构.成功实现了利用光子晶体结构增强LED的出光效率,与未制作光子晶体结构的LED相比,光子晶体结构LED的出光效率可在原来基础上提高1倍以上.并且随着晶格常数的增加,出光效率进一步提高.     

带有锥状反射结构的AlGaInP键合衬底LED

本研究通过光辅助化学腐蚀技术在衬底键合AlGaInP反极性发光二极管中制备出锥状反射镜结构提升器件的光提取效率。首先利用氢氟酸与双氧水在532nm激光的辐射下载GaP:Mg层制备出锥状腐蚀结构,然后将金属反射镜蒸镀在锥状结构之上制备锥状的反射镜结构。在完成全部芯片工艺后,测试结果表明锥状反射镜结构可以显著提升光提取效率,并在光通量测量中与表面粗化集成平板反射镜LED相比较,得到了18.55%的增强。     

Improved Extraction Efficiency of Light-Emitting Diodes by Modifying Surface Roughness With Anodic Aluminum Oxide Film

An anodic alumina oxide (AAO) film with nano-roughening is added on the top window layer of AlGaInP light-emitting diodes (LEDs) to improve the light extraction of the device. The AAO film has a natural porosity to provide light scattering centers at the surface, allowing an increase of light emission intensity with no loss of or damage to the semiconductor material. Further, the fabricated AAO film with a refractive index is about which is intermediate between those of air and the window layer of GaP. By inserting this layer between the ambient and GaP, it broadens the critical angle for light emission and reduces internal reflection. Experiments with laboratory-fabricated AlGaInP devices of conventional design demonstrated a 32% improvement in the luminous intensity at 20 mA for the device with the AAO layer. This letter shows by theory and experiment that AAO films can be used as a low-cost, easily implemented surface nano-roughening for improving extraction efficiency of AlGaInP LEDs.     

Titanium nitride as spreading layers for AlGaInP visible LEDs

Thin titanium nitride (TiN) films with low sheet resistance and high transparency were deposited on AlGaInP light-emitting diodes (LEDs) to improve light extraction from the LED surface. Comparison test devices were fabricated both with and without TiN spreading layers. Results show LED current crowding at high current is reduced for devices with TiN current spreading film, improving external efficiency. It is confirmed that TiN films are feasible as current spreading layers of AlGaInP LEDs.     

Improvement of AlGaInP light emitting diode by sulfide passivation

The brightness of AlGaInP light emitting diodes (LEDs) has been raised by a factor of 1.12 at 20 mA by sulfide passivation. Meanwhile, the sulfide also can decrease leakage current of AlGaInP LEDs at -2 V to nearly one thousandth of that in the as-fabricated device. The possible causes for the brightness increase of AlGaInP LEDs after sulfide treatment including surface roughness, reduction of Fresnel loss, and effective injection of carriers were demonstrated.     

Analysis and Simulation of Light Extraction of Light-Emitting Diodes:Simulation Efficiency

Two foundational factors (escape cone and transmissivity) about light extraction of light emitting diodes (LEDs) are discussed.According to these factors,a new process to simulate the light extraction of LEDs based on the Monte Carlo method has been provided.The improved method is to deal with the reflection and refraction of light (beam of light) at the interface between two mediums approximately.In addition,light extraction of traditional LEDs is simulated by different processes with the same structure and parameters.The results show that the reflection and refraction of light processed approximately are accurate enough for analyzing LEDs structure.This method saves much time and improves efficiency in the simulation of light extraction of LEDs.     

Analysis and Simulation of Light Extraction of Light-Emitting Diodes: Simulation Efficiency

Two foundational factors (escape cone and transmissivity) about light extraction of light emitting diodes (LEDs) are discussed. According to these factors, a new process to simulate the light extraction of LEDs based on the Monte Carlo method has been provided. The improved method is to deal with the reflection and refraction of light (beam of light) at the interface between two mediums approximately. In addition, light extraction of traditional LEDs is simulated by different processes with the same structure and parameters. The results show that the reflection and refraction of light processed approximately are accurate enough for analyzing LEDs structure. This method saves much time and improves efficiency in the simulation of light extraction of LEDs.     

High-brightness AlGaInP light emitting diodes

First commercially introduced in 1990, AlGaInP light emitting diodes (LEDs) currently are the highest (luminous) efficiency visible solid-state emitters produced to date in the red through yellow spectral regime. The attainment of this high-efficiency performance is a result of the development of advanced metalorganic chemical vapor deposition crystal growth techniques, which have facilitated the high-quality growth of this quaternary alloy as well as the implementation of complex device designs. Furthermore, the highest efficiency family of AlGaInP devices (based upon a transparent-substrate platform and commercially introduced in 1994) have been realized as result of the development and implementation of direct compound semiconductor wafer bonding technology. As a result, the luminous efficiency of AlGaInP LEDs exceeds or rivals that of unfiltered incandescent lamps and other conventional lighting sources. Further improvements in these techniques (and the realization of efficient, high-power LEDs) are expected to make AlGaInP LEDs even more competitive with conventional lamp technology, thus enhancing the position of LED's in many applications as a preferred lighting source     

Improvement in light-output efficiency of AlGaInP LEDs fabricated on stripe patterned epitaxy

Quaternary AlGaInP light-emitting diodes (LEDs) operating at a wavelength of 630 nm with a stripe-patterned omni-directional reflector (ODR) were fabricated. It is demonstrated that the geometrical shape of stripe-patterned structure improves the light extraction efficiency by increasing the extraction of guided light. The optical and electrical characteristics of stripe-patterned ODR LEDs are presented and compared to typical ODR and distributed Bragg reflector (DBR) LEDs with the same epitaxial structure and emitting wavelength. It is shown that the output power of the stripe-patterned ODR LED exceeds that of the typical ODR and DBR LEDs by a factor of 1.15 and 2 times, respectively, and with an acceptable forward voltage of about 2.2 V.     

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.     

Enhanced Light Extraction in GaInN Light-Emitting Diode With Pyramid Reflector

GaInN light-emitting diodes (LEDs) that employ a reflector consisting of an array of three-dimensional (3-D) SiO₂ pyramids and a Ag layer are demonstrated to have enhanced light extraction compared with GaInN LEDs with planar Ag reflector. Ray tracing simulations reveal that the pyramid reflector provides 14.1% enhancement in extraction efficiency. Consistent with the simulation, it is experimentally demonstrated that GaInN LEDs with the pyramid reflector show 13.9% higher light output than LEDs with a planar Ag reflector. The enhancement is attributed to the appearance of an additional escape cone for light extraction enabled by the 3-D pyramid reflector