Nanostructured LED Reflectors for Near-Normal Light Extraction
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Solution Overview
Problem
Conventional LED reflectors lead to light loss due to multiple bounces within the LED cavity, resulting in reduced efficiency, as they either absorb photons or require excessive thickness for effective reflection.
Innovation Solution
A reflective nanostructured layer, comprising a specular reflector and periodic nanoantennas, is used to redirect light at near-perpendicular incidence, minimizing bounces and enhancing light extraction by directing photons towards the substrate's exit surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a specular reflector (metal film or dielectric mirror) is used, then light reflection efficiency is improved, but photons are absorbed in the reflector causing energy loss
Solution Approach 1:
The patent changes the geometric parameters of the reflector by introducing a nanostructured surface with specific features (feature size 1-10 μm, depth 1-50 μm) rather than using a flat specular reflector. This parameter change enables the reflector to achieve both high reflection efficiency and minimal absorption loss by controlling light interaction at the nanoscale level.
Solution Approach 2:
The patent employs a composite reflector structure combining a base material (such as silicon nitride, silicon oxide, or metal) with a nanostructured surface layer. This composite approach allows the reflector to leverage the high reflectivity of the base material while the nanostructured surface minimizes absorption losses by controlling light penetration depth and interaction pathways.
2Loss of energy
If a diffuse reflector (volume scattering material) is used, then light scattering is improved, but reflector thickness must be increased (>150 μm) causing device complexity
Solution Approach 1:
The patent transforms the reflector from a thick volume scattering medium into a thin nanostructured surface layer by changing the dimensional parameters. The nanostructured features (1-10 μm size, 1-50 μm depth) provide sufficient scattering capability in a much thinner profile, reducing the reflector thickness from >150 μm to just a few micrometers while maintaining or improving scattering efficiency.
Solution Approach 2:
The patent implements a thin film nanostructured reflector that provides diffuse reflection functionality in a minimal thickness. The nanostructured surface layer acts as a flexible, thin optical element that achieves effective light scattering without requiring the substantial thickness of conventional diffuse reflectors, thereby simplifying device structure.
3Productivity
If the sapphire layer height is increased to extract more light, then light extraction is improved, but device volume increases
Solution Approach 1:
The patent changes the optical interaction parameters by introducing a nanostructured reflector with specific geometric features (feature size, depth, spacing) that enhance light extraction efficiency. This allows achieving high light extraction without increasing the sapphire layer height, as the nanostructured surface creates multiple reflection pathways and increases the effective optical path length within the existing volume.
Solution Approach 2:
The patent addresses light extraction by moving from a volume-based solution (increasing sapphire height) to a surface-based solution (nanostructuring the reflector surface). The nanostructured features create optical effects at the surface dimension that influence light propagation throughout the device, enabling enhanced extraction efficiency without increasing the third dimension (height/volume).
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution increases LED efficiency by reducing light absorption and the need for thick reflectors, allowing more light to be emitted while maintaining a thin, low-loss reflector design.
Implementation Method 1
a reflective nanostructured layer... configured to reflect toward and through a side wall surface of the substrate light that is emitted by the semiconductor structure and incident on the reflective nanostructured layer at angles at or near perpendicular incidence
Data Source
AI summary
A light emitting device comprises a semiconductor diode structure configured to emit light, a substrate that is transparent to light emitted by the semiconductor diode structure, and a reflective nanostructured layer. The reflective nanostructured layer may be disposed on or adjacent to a bottom surface of the substrate and configured to reflect toward and through a side wall surface of the substrate light that is emitted by the semiconductor structure and incident on the reflective nanostructured layer at angles at or near perpendicular incidence. Alternatively, the reflective nanostructured layer may be disposed on or adjacent to at least one sidewall surface of the substrate and configured to reflect toward and through the bottom surface of the substrate light that is emitted by the semiconductor structure and incident on the reflective nanostructured layer at angles at or near perpendicular incidence.