Silver Electrode Adhesion in Semiconductor Light Emitting Devices
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Solution Overview
Problem
Semiconductor light emitting devices face challenges with silver electrodes due to poor adhesion, chemical reactions, and deteriorating reflecting characteristics, especially when sintering is performed, which affects the electrical and optical performance.
Innovation Solution
A semiconductor light emitting device is designed with a stacked structural unit comprising a nitride semiconductor layer and an electrode structure that includes a silver or silver alloy layer paired with a noble metal layer, such as platinum, palladium, or iridium, where the noble metal is concentrated at the interface between the layers, and sintered in an oxygen-containing atmosphere to maintain reflectivity and adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If sintering is performed to improve adhesion, then adhesion is improved, but reflecting characteristics deteriorate
Solution Approach 1:
The electrode is divided into multiple functional layers: a silver-based first metal layer for high reflectance, a noble metal-containing second metal layer for migration suppression, and an interface layer for adhesion enhancement. This segmentation allows each layer to optimize its specific function without compromising others.
Solution Approach 2:
The electrode uses a composite structure combining silver (for reflectance) with noble metals like Pt, Pd, Rh, Ir, Ru, or Os (for stability and migration suppression). The noble metal concentration increases toward the interface with the semiconductor layer, creating a gradient composite material that simultaneously achieves adhesion, stability, and reflectance.
2Strength
If sintering is performed at high temperature to improve adhesion, then adhesion is improved, but reflecting characteristics easily deteriorate
Solution Approach 1:
The sintering temperature is controlled within a specific range (800°C to 1050°C) to achieve optimal adhesion while preventing excessive grain growth that would deteriorate reflectance. The noble metal concentration gradient is also optimized to suppress migration at these temperatures.
Solution Approach 2:
The interface layer containing silver and the noble metal concentration gradient act as intermediaries between the silver first metal layer and the semiconductor layer. This interface structure enhances adhesion at high temperatures while the noble metal prevents silver migration and maintains reflecting characteristics.
3Stability of the object's composition
If a metal layer is formed to cover silver electrode to prevent migration, then migration is suppressed, but electrical characteristics deteriorate
Solution Approach 1:
The noble metal is not uniformly distributed but concentrated in the interface layer near the semiconductor contact. This local concentration provides migration suppression exactly where needed at the interface, while the bulk silver layer maintains its excellent electrical conductivity and reflectance properties.
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 enhances the reflectivity, electrical characteristics, and adhesion of the silver electrode, leading to improved luminance, efficiency, and reliability of the semiconductor light emitting device while controlling grain growth and migration.
Implementation Method 1
a concentration of the element in a region including an interface between the first metal layer and the second semiconductor layer being higher than a concentration of the element in a region of the first metal layer distal to the interface
Implementation Method 2
sintering the second semiconductor layer, the first metal layer, and the second metal layer in an atmosphere containing oxygen, a temperature of the sintering causing an average particle diameter of the silver included in the first metal layer after the sintering to be not more than three times an average particle diameter of the silver prior to the sintering
Implementation Method 3
a first metal layer including silver or silver alloy and being provided on a side of the second semiconductor layer opposite to the light emitting layer
Data Source
AI summary
A semiconductor light emitting device, includes: a stacked structural unit including a first semiconductor layer of a first conductivity type, a second semiconductor layer of a second conductivity type, and a light emitting layer provided therebetween; and an electrode including a first and second metal layers, the first metal layer including silver or silver alloy and being provided on a side of the second semiconductor layer opposite to the light emitting layer, the second metal layer including at least one element selected from gold, platinum, palladium, rhodium, iridium, ruthenium, and osmium and being provided on a side of the first metal layer opposite to the second semiconductor layer. A concentration of the element in a region including an interface between the first and second semiconductor layers is higher than that of the element in a region of the first metal layer distal to the interface.