LED Reflective Electrode Structure for Light Extraction
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Solution Overview
Problem
Contemporary light emitting diodes (LEDs) suffer from inefficiency due to internal absorption of light, limiting their brightness and suitability for applications beyond indicator use, such as general illumination.
Innovation Solution
A reflective electrode structure is implemented, featuring a metal electrode with a thick, optically transmissive dielectric layer and a distributed Bragg reflector (DBR) pair, which enhances light reflection and reduces absorption by making electrical contact through an ohmic layer, allowing light to be redirected back into the semiconductor material for extraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a metal electrode is used in contemporary LEDs, then electrical contact is achieved, but light absorption increases and efficiency decreases
Solution Approach 1:
The electrode structure is segmented into distinct functional zones: a suspended portion over the active area that does not absorb light, and contact portions at the periphery that provide electrical connection. This segmentation allows the electrode to simultaneously minimize light absorption and maintain reliable electrical contact.
Solution Approach 2:
A dielectric layer is introduced as an intermediary between the metal electrode and the semiconductor substrate. This dielectric mediator allows electrical contact to be achieved through controlled pathways while preventing direct contact between the metal and light paths, thereby reducing light absorption.
2Reliability
If the electrode area is increased to improve electrical contact, then reliability improves, but light absorption increases and brightness decreases
Solution Approach 1:
The electrode is divided into a suspended central portion and peripheral contact portions. The suspended portion is positioned over the active emission area without contacting it, eliminating light absorption in this region. The peripheral portions provide adequate electrical contact area without interfering with the light emission zone, thus maintaining brightness while ensuring reliability.
Solution Approach 2:
The electrode structure utilizes vertical dimension by suspending the central portion above the substrate using a dielectric layer. This dimensional change allows the electrode to provide electrical contact through vertical pathways while maintaining horizontal separation from the light emission area, preventing light absorption.
3Loss of energy
If a thick dielectric layer is used to reduce light absorption, then efficiency improves, but device complexity increases
Solution Approach 1:
The dielectric layer is extracted and positioned only in specific regions where it is needed - beneath the suspended electrode portions - rather than being a universal layer throughout the device. This selective placement reduces the overall complexity of the device structure while still achieving the goal of reducing light absorption in critical areas.
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 increases the brightness and efficiency of LEDs, making them more suitable for a wider range of applications, including general illumination by minimizing light absorption and maximizing light extraction.
Implementation Method 1
The electrode cooperates with the thick dielectric to enhance reflection such that light emitted in the direction of the electrode is reflected back into the semiconductor material
Implementation Method 2
A series of one or more pairs of DBR dielectric layers can be formed between the thick dielectric layer and the metal electrode such that each DBR dielectric layer of this pair can be optically transmissive, of different indices of refraction from each other
Data Source
AI summary
An electrode structure is disclosed for enhancing the brightness and/or efficiency of an LED. The electrode structure can have a metal electrode and an optically transmissive thick dielectric material formed intermediate the electrode and a light emitting semiconductor material. The electrode and the thick dielectric cooperate to reflect light from the semiconductor material back into the semiconductor so as to enhance the likelihood of the light ultimately being transmitted from the semiconductor material. Such LED can have enhanced utility and can be suitable for uses such as general illumination. The semiconductor material can have a cutout formed therein and a portion of the electrode can be formed outside of the cutout and a portion of the electrode can be formed inside of the cutout. The portion of the electrode outside the cutout can be electrically isolated from the semiconductor material by the dielectric material.