Conductive omni-directional reflectors for spontaneously emitting light sources

0401075 Schubert基于半导体的自发发光光源用于照明、传感、通信和标牌等多种应用。将光从发光材料有效地提取到自由空间中对于这种光源的未来发展至关重要。有两种基本的方法能够在自发发射器中实现有效的光提取，即采用具有近乎完美的透明度的结构或采用具有近乎完美的反射特性的光学反射器。这样的反射器应当以非常低的光学损耗反射光，而与入射角和波长无关。一个非常有意义和技术相关性的问题是关于满足这些要求的反射器的最佳类型。这里提出了一种新型的反射器，它具有（i）高反射率，（ii）全向特性，（iii）导电性，（iv）宽光谱范围。反射器由半导体、由微接触阵列穿孔的低折射率电介质层和金属层组成。结果表明，这种三层全向反射器（ODR）具有99%的反射率，具有弱的角度依赖性，从而显着提高自发发射源的光提取效率。这种新型的ODR与金属反射镜和分布布拉格反射镜相比具有很好的性能。使用新的ODR演示GaInN和AlGaInP LED的性能改进将是该项目的一个组成部分。已知这些LED具有低金属接触反射率（GaInN LED）和在分布式布拉格反射器（AlGaInP LED）中在倾斜入射角处缺乏反射率的缺点。

0401075SchubertSpontaneously-emitting light sources based on semiconductors are used in applications as diverse as lighting, sensing, communications, and signage. The efficient extraction of light from the light-emitting material into free space is essential for the future advancement of such light sources. There are two fundamental approaches enabling efficient light extraction in spontaneous emitters, namely the employment of structures with near-perfect transparency or the employment of optical reflectors with near-perfect reflection characteristics. Such reflectors should reflect light with very low optical losses irrespective of the angle of incidence and wavelength. A question of great intellectual interest and technical relevance concerns the optimum type of reflector that meets these requirements.Here a novel type of reflector is proposed that possesses (i) high reflectivity, (ii) omni-directional characteristics, (iii) electrical conductivity, and (iv) broad spectral range. The reflector consists of a semiconductor, a low-refractive-index dielectric layer perforated by an array of micro-contacts, and a metal layer. It is shown that such a triple-layer omni-directional reflector (ODR) has reflectivities 99 % with a weak anglular dependence thereby significantly increasing the light-extraction efficiency in spontaneously-emitting sources. The new type of ODR compares very favorably with the well-known metal reflector and distributed Bragg reflector. The demonstration of performance improvements in GaInN and AlGaInP LEDs using the new ODR will be an integral part of the project. It is known that these LEDs suffer from low metal-contact reflectivity (GaInN LEDs) and the lack of reflectivity at oblique angles of incidence in distributed Bragg reflectors (AlGaInP LEDs).