AlGaInP LED Double Reflective Layers for High Efficiency
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Solution Overview
Problem
AlGaInP-based red LEDs have low light-emission efficiency due to light absorption by the gallium arsenide substrate and limited reflectivity of single reflective metal layers, which also risk diffusion and index drop at high temperatures.
Innovation Solution
An AlGaInP-based LED with double reflective layers, comprising a distributed Bragg reflector and a reflective metal layer, where the distributed Bragg reflector is grid-like and formed on an epitaxial layer with openings for the metal layer, and a permanent substrate bonded to the metal layer, enhancing reflectivity and avoiding substrate absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single reflective metal layer is used, then the structure is simple, but the reflectivity is limited to less than 90%
Solution Approach 1:
The patent combines a distributed Bragg reflector (DBR) and a reflective metal layer to form a composite reflective structure. The DBR consists of multiple alternating layers of high and low refractive index materials, which when combined with the metal layer, achieves over 99% reflectivity. This composite structure resolves the contradiction by sacrificing some structural simplicity to gain significantly improved reflectivity.
2Illumination intensity
If a reflective metal layer is used, then reflectivity improves, but metal diffusion at high temperature causes index drop
Solution Approach 1:
The patent introduces an intermediary layer between the reflective metal layer and the semiconductor layer. This intermediary layer acts as a diffusion barrier that prevents metal atoms from migrating into the semiconductor at high temperatures during operation, thereby maintaining the refractive index and optical properties. This resolves the contradiction by protecting the system from thermal degradation while preserving the high reflectivity benefits.
3Reliability
If the GaAs substrate is used, then the substrate is permanent and stable, but it absorbs red light reducing emission efficiency
Solution Approach 1:
The patent extracts or removes the light-absorbing GaAs substrate from the final LED structure. Instead, a reflective metal layer is bonded to the back of the semiconductor device, and the GaAs substrate is detached and discarded. This extraction eliminates the harmful light absorption effect while the reflective metal layer provides the beneficial reflection of red light, resolving the contradiction between substrate stability and light absorption.
4Illumination intensity
If multiple layers (metal layer, dielectric layer, unalloy ohmic contact layer) are used to maintain reflectivity, then reflectivity is improved, but the structure becomes complex and manufacturing is difficult
Solution Approach 1:
The patent merges the reflective metal layer with the ohmic contact function by directly bonding the metal layer to the semiconductor without requiring separate dielectric and unalloy ohmic contact layers. The metal layer is designed to provide both optical reflection and electrical contact, reducing the total number of layers from three or more to a single integrated layer. This merging resolves the contradiction by simplifying the structure while maintaining both high reflectivity and proper electrical contact.
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
The double reflective layers achieve a reflectivity of over 99% and improve light-emission efficiency by 20%, simplifying the LED structure and reducing absorption, while maintaining the reflective metal layer's effectiveness as an ohmic contact.
Implementation Method 1
a distributed Bragg reflector formed on a top of the epitaxial layer
Implementation Method 2
the arrangement of the distributed Bragg reflector is grid-like with a portion of the top of the epitaxial layer exposed
Implementation Method 3
a reflective metal layer formed on the distributed Bragg reflector and on the exposed portion of the top of the epitaxial layer
Implementation Method 4
An LED is a semiconductor diode, converting electrical energy into light energy, and emitting visible (e.g. yellow, green and blue), infrared or ultraviolet light
Data Source
AI summary
The invention discloses an AlGaInP-based LED with double reflective layers and a fabrication method thereof. The method includes: providing a temporary substrate; forming an epitaxial layer on a front of the temporary substrate; forming a distributed Bragg reflector on the epitaxial layer; forming an some openings in the distributed Bragg reflector, such that the arrangement of the distributed Bragg reflector is grid-like and a portion of a top of the epitaxial layer is exposed; forming a reflective metal layer on the distributed Bragg reflector and on the exposed portion of the top of the epitaxial layer, to fill the openings; bonding a permanent substrate onto the reflective metal layer; removing the temporary substrate; forming a first electrode and a second electrode at a bottom of the epitaxial layer and a top of the permanent substrate, respectively; and dicing to obtain the AlGaInP-based LED chips. The AlGaInP-based LED with both the distributed Bragg reflector and the reflective metal layer according to the invention can fully utilize good reflectivity of the reflective layers to the extreme, and improve the light-emission efficiency of the AlGaInP-based LED effectively.