Transparent Conductive Electrodes for Red LED Light Extraction
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Solution Overview
Problem
Red and infrared LEDs suffer from low light extraction efficiency due to light absorption by the GaAs substrate and conventional gold-based electrodes, which also experience inter-diffusion issues during thermal treatment, limiting the improvement of optical power.
Innovation Solution
A p-side up LED structure with a thin ohmic electrode pattern and a transparent conductive metal oxide pattern is used, featuring a metal reflection layer, transparent insulating layer, and n-type GaAs plug, along with a p-type GaP window layer, to reduce optical loss and enhance current spreading, employing materials like indium tin oxide (ITO) and gallium-doped zinc oxide (IGZO) for improved reflectance and transmittance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional gold-based electrode is used, then good electrical contact is achieved, but light absorption increases and light extraction efficiency decreases
Solution Approach 1:
The electrode is divided into multiple functional layers: a thin gold layer (10-50 nm) for electrical contact, followed by a transparent conductive oxide layer (ITO, IGZO, or AZO) for light transmission. This segmentation allows each layer to perform its specialized function without compromising the other.
Solution Approach 2:
The electrode structure uses a composite of金属材料 (gold) and transparent conductive oxide materials (ITO, IGZO, AZO). The gold layer provides excellent electrical conductivity and contact, while the transparent oxide layer provides high optical transmittance in the red wavelength range, creating a composite electrode that satisfies both electrical and optical requirements.
2Ease of manufacture
If the GaAs substrate is used, then device fabrication is simplified, but light absorption by the substrate increases optical loss
Solution Approach 1:
The GaAs substrate is completely removed through wet etching processes. The LED structure is transferred to a suspended membrane configuration where the active layer is released from the substrate, eliminating the source of light absorption entirely while maintaining device functionality through alternative support structures.
Solution Approach 2:
A transparent insulating layer (such as SiO2 or Si3N4) is introduced as an intermediary between the active layer and the external environment. This layer serves as both a structural support after substrate removal and an optical window that does not absorb red light, replacing the substrate's structural role without its harmful optical properties.
3Reliability
If thermal treatment is applied, then electrode properties are improved, but inter-diffusion occurs reducing reflectance
Solution Approach 1:
The patent employs low-cost, easily replaceable transparent conductive oxide materials (ITO, IGZO, AZO) that can be deposited as thin films. These materials provide sufficient electrical conductivity and optical transmittance without requiring complex protective structures or low-temperature processing, effectively replacing the need for high-temperature thermal treatment that causes inter-diffusion.
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 solution significantly increases light extraction efficiency by minimizing absorption and enhancing current spreading, achieving high transmittance and low contact resistance, thereby improving the overall optical power of the LED device.
Implementation Method 1
a transparent conductive metal oxide pattern (144) provided on the p ohmic contact layer (142)... allowing red or infrared light-emitting diodes to have improved light extraction efficiency
Implementation Method 2
a metal reflection layer (174) provided on the conductive substrate (176)
Implementation Method 3
an active layer (126) provided on the n cladding layer (121)... light generated in the active layer
Data Source
AI summary
A light-emitting diode device may include a conductive substrate, a metal reflection layer provided on the conductive substrate, a transparent insulating layer provided on the metal reflection layer, an n ohmic contact plug provided in a lower portion of each of through holes formed in the transparent insulating layer, an n-type gallium arsenide (GaAs) plug provided in an upper portion of the through hole, an n cladding layer provided on the transparent insulating layer, an active layer provided on the n cladding layer, a p cladding layer provided on the active layer, a p-type GaP window layer provided on the p cladding layer, a p ohmic contact pattern provided on the p-type GaP window layer, a transparent conductive metal oxide pattern provided on the p ohmic contact layer, and a p electrode pad provided on the transparent conductive metal oxide.