LED Light Redirection Layer for Low-Bounce Photon Extraction
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Solution Overview
Problem
Conventional light-emitting diodes (LEDs) face challenges in achieving high photon extraction efficiency due to total internal reflection, requiring a large number of photon bounces and potentially increasing costs or complexity.
Innovation Solution
The light-emitting device incorporates a semiconductor diode structure with an anti-reflection coating on the front surface and a redirection layer on the back surface, which includes nano-antennae, photonic bandgap structures, or meta-atoms to redirect light and enhance extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If texturing is formed on the front surface to extract light, then light extraction efficiency is improved, but the number of photon bounces increases requiring low optical loss per round trip
Solution Approach 1:
The patent applies preliminary action by forming a roughness layer during the semiconductor growth process itself, rather than adding it separately afterward. This integration ensures that the light extraction structure is built in conjunction with the active layers, reducing subsequent manufacturing steps and potential damage to the structure.
Solution Approach 2:
The patent merges the light extraction function with the semiconductor growth process by forming the roughness layer concurrently with growing the light-emitting active layers. This combining of functions eliminates the need for separate texturing steps and reduces overall device complexity.
2Productivity
If a back-surface reflector is used to redirect light, then light recirculation is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the light redirection function from a separate back-surface reflector structure and integrates it directly into the semiconductor diode structure itself. The roughness layer performs both light extraction and redirection functions, eliminating the need for a distinct reflector component.
Solution Approach 2:
The roughness layer serves multiple functions simultaneously: it extracts light from the active layers, redirects light toward the front surface, and eliminates the need for a separate reflector. This multi-functionality reduces device complexity while maintaining light recirculation efficiency.
3Productivity
If multiple photon bounces are required for extraction, then extraction efficiency can reach 90%, but optical loss per round trip must be sufficiently low increasing cost
Solution Approach 1:
The patent applies local quality by creating a roughness layer with specific local structural properties that enhance light extraction at the front surface. The non-uniform roughness structure provides localized light redirection paths that reduce the number of bounces required, thereby reducing cumulative optical losses.
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 achieves a photon extraction efficiency greater than 80%, with a reduced number of photon bounces, thereby improving the device's performance while potentially lowering costs and complexity.
Implementation Method 1
an anti-reflection coating on the front surface of the semiconductor diode structure that exhibits reflectivity, for light incident on the front surface within the semiconductor diode structure at an incidence angle less than the critical angle, that is less than corresponding Fresnel reflectivity
Implementation Method 2
Many semiconductor materials have relatively large refractive indices (often around 3 or more) which would result in a large fraction of the emitted light being trapped within the semiconductor diode structure by total internal reflection
Data Source
AI summary
A light-emitting device includes a semiconductor diode structure with one or more light-emitting active layers, an anti-reflection coating on its front surface, and a redirection layer on its back surface. Active-layer output light propagates within the diode structure. The anti-reflection coating on the front surface increases transmission of active-layer output light incident below the critical angle Θc. Active-layer output light incident on the redirection layer at an incidence angle greater than Θc is redirected to propagate toward the front surface at an incidence angle that is less than Θc. Device output light is transmitted by the front surface to propagate in an ambient medium, and includes first and second portions of the active-layer output light incident on the front surface at an incidence angle less than Θc, the first portion without redirection by the redirection layer and the second portion with redirection by the redirection layer.