Inverted Light Extraction Interface with Dual-Scale Roughness

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Solution Overview

Problem

Light trapping and absorption issues in semiconductor emitting devices, such as LEDs, due to refractive index differences between layers and interfaces, result in significant losses of emitted light, with existing solutions only partially alleviating these problems through roughness and Fresnel losses.

Innovation Solution

The introduction of an interface with a first profiled surface featuring large roughness components and a second profiled surface with small roughness components, where the first characteristic scale is approximately an order of magnitude larger than the second, to enhance light extraction by providing additional surfaces for reflection and refraction, and using a bonding material and filler to facilitate light propagation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If roughness is introduced at interfaces to alleviate light trapping, then light extraction is improved, but Fresnel losses still cause significant light reflection and transmission loss

Engineering Contradiction:

Improvelight extraction efficiencyVSAvoidinterface structure complexity

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

The interface is segmented into multiple distinct layers with different roughness characteristics. The first interface has large roughness components while the second interface has small roughness components, creating a graduated transition structure that systematically addresses light extraction at different scales rather than using a single uniform interface

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the interface structure are given different roughness properties tailored to their specific functions. The first interface region uses large roughness for primary light extraction, while the second interface region uses small roughness for fine-tuning and reducing Fresnel losses, optimizing each local region for its specific role

Inventive Principle:

Principle #3Local quality

2Loss of energy

If large roughness components are used at the first interface, then total internal reflection is reduced, but the interface complexity and manufacturing difficulty increase

Engineering Contradiction:

Improvetotal internal reflection lossVSAvoidinterface fabrication ease

Core Design Contradiction:

Loss of energyVSEase of manufacture

Solution Approach 1:

The fabrication process is segmented into distinct stages corresponding to the two interfaces. Large roughness components are formed first, then small roughness components are added in a subsequent stage, allowing each fabrication step to be optimized independently and simplifying the overall manufacturing process

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The large roughness components are formed in advance as a preliminary step before adding the small roughness components. This preliminary action establishes the primary light extraction structure first, making the subsequent fine-detail work easier and more controlled

Inventive Principle:

Principle #10Preliminary action

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 configuration significantly increases the amount of light that escapes the device, reducing total internal reflection and Fresnel losses, thereby enhancing the overall light extraction efficiency and output of the emitting device.

Implementation Method 1

A larger change in the index of refraction between the layers, and between the substrate and its surroundings, results in a smaller total internal reflection (TIR) angle

Methodology Applied

Scientific EffectTotal internal reflection: Total Internal Reflection

Implementation Method 2

Fresnel losses are associated with light partially reflected at the interface for all the incident light angles

Methodology Applied

Scientific EffectFresnel losses:

Implementation Method 3

Light is generated with uniform angular distribution and escapes the LED die by traversing semiconductor layers in all directions

Methodology Applied

Scientific EffectRefraction: Refraction

Data Source

PatentUS9048378B2Device with inverted large scale light extraction structures

Publication Date: 2015.06.02 SENSOR ELECTRONIC TECHNOLOGY INC

AI summary

An interface including roughness components for improving the propagation of radiation through the interface is provided. The interface includes a first profiled surface of a first layer comprising a set of large roughness components providing a first variation of the first profiled surface having a first characteristic scale and a second profiled surface of a second layer comprising a set of small roughness components providing a second variation of the second profiled surface having a second characteristic scale. The first characteristic scale is approximately an order of magnitude larger than the second characteristic scale. The surfaces can be bonded together using a bonding material, and a filler material also can be present in the interface.