Reflective LED Die for Light Extraction
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Solution Overview
Problem
Conventional phosphor-converted LEDs face inefficiencies due to low reflectivity of metal contacts and internal reflections, limiting light extraction and package efficiency.
Innovation Solution
Incorporating highly reflective regions on the LED die, either as metal layers or distributed Bragg reflectors, to enhance light reflection and reduce internal reflections, while maintaining electrical functionality and mechanical support by retaining the transparent growth substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional metal contacts are used in phosphor-converted LEDs, then electrical functionality is achieved, but reflectivity is insufficient leading to light loss
Solution Approach 1:
The patent combines the electrical contact function and the light reflection function into a single integrated metal contact layer. This eliminates the need for separate reflective layers while achieving both electrical connectivity and high reflectivity, thereby reducing light loss without increasing device complexity
Solution Approach 2:
The metal contact layer is designed to serve multiple functions simultaneously: providing electrical contact to the semiconductor layer and acting as a highly reflective mirror for upward-directed light. This multi-functionality resolves the contradiction by achieving high reflectivity without adding separate structural elements
2Productivity
If the growth substrate is removed to improve light extraction, then package efficiency increases, but mechanical support and structural stability are compromised
Solution Approach 1:
The patent performs preliminary roughening of the lower semiconductor layer surface before final device assembly. This pre-treatment creates a textured surface that enhances light extraction efficiency while the layer itself maintains structural integrity, resolving the contradiction between light extraction and mechanical stability
Solution Approach 2:
The patent applies localized roughening only to the lower semiconductor layer surface where light extraction is needed, while maintaining smooth surfaces and intact structure in other critical areas. This localized treatment improves light extraction without compromising overall structural stability
3Productivity
If internal reflections are reduced to improve light extraction, then package efficiency increases, but device complexity increases
Solution Approach 1:
The patent combines the roughening treatment directly into the semiconductor layer structure itself, eliminating the need for separate anti-reflective coatings or additional structural elements. This integrated approach reduces internal reflections and improves package efficiency without increasing device complexity
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
Significantly increases the reflectivity of the LED die, leading to improved light extraction and package efficiency, resulting in enhanced luminous efficacy and brighter LED performance.
Implementation Method 1
the wavelength-converted light emitted by the phosphor is combined with the blue light that leaks through the phosphor. Most of this light is then reflected back upwards by the metal contacts on the bottom surface of the LED die
Implementation Method 2
Incorporating highly reflective regions on the LED die, either as metal layers or distributed Bragg reflectors
Implementation Method 3
The blue light energizes the phosphor, and the wavelength-converted light emitted by the phosphor
Data Source
Figure 1~3
Figure 4~5
Figure 6~7
AI summary
An LED die (40) includes an N-type layer (18), a P-type layer (22), and an active layer (20) epitaxially grown over a first surface of a transparent growth substrate (46). Light is emitted through a second surface of the substrate opposite the first surface and is wavelength converted by a phosphor layer (30). Openings (42, 44) are etched in the central areas (42) and along the edge (44) of the die to expose the first surface of the substrate (46). A highly reflective metal (50), such as silver, is deposited in the openings and insulated from the metal P-contact. The reflective metal may conduct current for the N- type layer by being electrically connected to an exposed side of the N-type layer along the inside edge of each opening. The reflective metal reflects downward light emitted by the phosphor layer to improve efficiency. The reflective areas provided by the reflective metal may form 10%-50% of the die area.