LED Mirror Reflectivity via Barrier Layer Segmentation
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Solution Overview
Problem
Conventional LED chips face reduced light extraction efficiency due to the light-absorbing effects of metal barrier layers, particularly when these layers extend beyond the periphery of the mirror, leading to absorption of photons that would otherwise contribute to emission.
Innovation Solution
The barrier layers are designed to be smaller than the mirror, minimizing their exposure and reducing the area where they can absorb light, with an insulator and a highly reflective metal layer forming a composite barrier to enhance reflectivity and prevent Ag migration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If barrier layers extend beyond the periphery of the mirror to provide complete coverage and prevent metal migration, then reliability is improved, but light extraction efficiency deteriorates due to light absorption by the barrier layer
Solution Approach 1:
The barrier layer is segmented into two distinct regions: a first barrier layer portion that contacts the mirror and provides migration prevention, and a second barrier layer portion that is removed to expose the mirror periphery. This segmentation allows the barrier to fulfill its protective function while eliminating the light-absorbing portion that extends beyond the mirror.
Solution Approach 2:
The second portion of the barrier layer is completely removed (taken out) from the structure. This extraction eliminates the harmful light-absorbing element while preserving the essential barrier function at the mirror interface, thereby resolving the contradiction between reliability and light extraction efficiency.
2Reliability
If a metal barrier layer is used to prevent Ag migration, then reliability is improved, but light absorption increases reducing emission efficiency
Solution Approach 1:
The barrier layer is designed with local quality variation: it is present where needed (contacting the mirror to prevent Ag migration) and absent where harmful (beyond the mirror periphery where it would absorb light). This spatially differentiated structure optimizes both reliability and optical performance.
Solution Approach 2:
The potential harm of the barrier layer extending beyond the mirror is converted into a benefit by selectively removing that portion. The exposed mirror periphery, previously obscured by the light-absorbing barrier, now directly reflects light, transforming the defect into an optical enhancement.
3Reliability
If barrier layer completely covers mirror to ensure protection, then reliability is improved, but external quantum efficiency deteriorates due to reduced light reflection
Solution Approach 1:
The barrier layer is segmented into a protective portion (first portion contacting the mirror) and a removed portion (second portion beyond the mirror). This segmentation maintains protection where necessary while maximizing light extraction efficiency by eliminating the obstructive portion.
Solution Approach 2:
Instead of complete coverage, a partial barrier layer is used—sufficient to protect the mirror from Ag migration but limited in extent to avoid light absorption. This partial action achieves the minimum necessary protection while optimizing optical performance.
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 improves the light extraction and external quantum efficiency of LED chips by minimizing the light-absorbing effects of the barrier layers, resulting in enhanced emission characteristics and reduced dimming effects, especially in multi-junction chips.
Implementation Method 1
The first contact comprises a highly reflective mirror
Implementation Method 2
a barrier layer adjacent the mirror... to prevent Ag migration
Data Source
AI summary
Embodiments of the present invention are generally related to LED chips having improved overall emission by reducing the light-absorbing effects of barrier layers adjacent mirror contacts. In one embodiment, a LED chip comprises one or more LEDs, with each LED having an active region, a first contact under the active region having a highly reflective mirror, and a barrier layer adjacent the mirror. The barrier layer is smaller than the mirror such that it does not extend beyond the periphery of the mirror. In another possible embodiment, an insulator is further provided, with the insulator adjacent the barrier layer and adjacent portions of the mirror not contacted by the active region or by the barrier layer. In yet another embodiment, a second contact is provided on the active region. In a further embodiment, the barrier layer is smaller than the mirror such that the periphery of the mirror is at least 40% free of the barrier layer, and the second contact is below the first contact and accessible from the bottom of the chip.