Multiple Reflection Layer Electrode for Nitride Semiconductor Light Emitting Devices
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Solution Overview
Problem
Conventional semiconductor light emitting devices, particularly those using nitride semiconductors, face issues with agglomeration of the p-type electrode during annealing, leading to reduced reflectivity and optical output due to differences in surface energies between the nitride semiconductor and metal materials like silver.
Innovation Solution
A multiple reflection layer electrode is designed with a reflection layer, an agglomeration protecting layer (APL), and a diffusion barrier to prevent agglomeration and diffusion, along with an oxidation protecting layer to maintain thermal stability and ohmic contact characteristics, using materials like Ag, Al, and transparent conductive materials to reduce contact resistance and prevent void formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a p-type electrode is formed of a conductive metal with increased reflectivity (e.g., Ag) on a p-type nitride semiconductor layer, then light extraction efficiency is improved, but agglomeration occurs during annealing due to surface energy differences, leading to reduced reflectivity and optical output
Solution Approach 1:
An agglomeration protecting layer (APL) is introduced as an intermediary between the p-type nitride semiconductor layer and the silver reflection layer. This APL has surface energies that are intermediate between the semiconductor and metal, preventing direct contact and the resulting agglomeration while maintaining light extraction efficiency through the multi-layer structure.
Solution Approach 2:
The electrode structure is transformed from a single-material silver layer into a composite multi-layer structure consisting of the p-type nitride semiconductor layer, agglomeration protecting layer, silver reflection layer, and diffusion barrier layer. This composite structure combines materials with different properties to simultaneously achieve high reflectivity, prevent agglomeration, and block diffusion.
2Reliability
If annealing is performed to reduce resistance of the p-type electrode, then contact resistance is reduced, but agglomeration and void formation occur, lowering reflectivity and optical output
Solution Approach 1:
The agglomeration protecting layer serves as a mediator that enables the annealing process to proceed without causing agglomeration. During annealing, the APL prevents direct interaction between the silver atoms and the nitride semiconductor surface, allowing resistance reduction while maintaining structural integrity and reflectivity.
Solution Approach 2:
The agglomeration protecting layer is deposited on the nitride semiconductor layer before the silver reflection layer is formed. This preliminary action prepares the surface to prevent agglomeration during subsequent annealing processes, ensuring that when annealing is performed to reduce resistance, the optical output is preserved.
3Device complexity
If a single-layer p-type electrode is used, then device complexity is reduced, but thermal stability and ohmic contact characteristics are insufficient
Solution Approach 1:
The single-layer p-type electrode is segmented into multiple functional layers: the p-type nitride semiconductor layer provides ohmic contact, the agglomeration protecting layer prevents surface energy mismatch, the silver reflection layer provides high reflectivity, and the diffusion barrier layer prevents material diffusion. Each layer performs a specific function to collectively achieve thermal stability and ohmic contact characteristics.
Solution Approach 2:
The electrode is constructed as a composite multi-layer structure where each layer is made of materials with specific properties tailored to its function. This composite structure achieves thermal stability and ohmic contact characteristics that cannot be obtained with a single material, while the layered design systematically addresses each technical requirement.
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 effectively prevents agglomeration and maintains high reflectivity, enhancing the thermal stability and optical output of nitride-based semiconductor light emitting devices by reducing contact resistance and preventing oxidation, thus improving the brightness and reliability of the devices.
Implementation Method 1
a diffusion barrier between the reflection layer and the APL so as to prevent or retard diffusion of the APL
Implementation Method 2
Light emitted from the active layer 14 may be reflected by the p-type electrode 30 and may be emitted to the outside of the semiconductor LED 50 through the sapphire substrate 10
Data Source
AI summary
Provided are a multiple reflection layer electrode, a compound semiconductor light emitting device having the same and methods of fabricating the same. The multiple reflection layer electrode may include a reflection layer on a p-type semiconductor layer, an APL (agglomeration protecting layer) on the reflection layer so as to prevent or retard agglomeration of the reflection layer, and a diffusion barrier between the reflection layer and the APL so as to retard diffusion of the APL.