Multilayer Nitride Semiconductor Electrodes for Low Resistance
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Solution Overview
Problem
Nitride semiconductor LEDs face challenges with high contact resistance due to large energy band-gaps in p-type and n-type layers, leading to increased operational voltage and heating, as well as reduced light extraction efficiency due to low reflectivity of Cr/Au electrodes.
Innovation Solution
The implementation of a multilayer structure for the n-electrode and p-electrode, including an ohmic contact layer, a compound layer with aluminum or silver, and a degradation preventing layer, which enhances ohmic contact resistance, adhesive force, and reflectivity, while preventing degradation and oxidation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If Cr/Au electrodes are used for p-type and n-type nitride semiconductor layers, then the manufacturing process is simplified, but the contact resistance increases due to large energy band-gap
Solution Approach 1:
The electrode structure is segmented into multiple functional layers: Cr layer for ohmic contact with nitride semiconductor, Al or Ag layer for low resistance and conductivity, and Au layer for wire bonding. This segmentation allows each layer to optimize for its specific function, resolving the contradiction between ease of manufacture and low contact resistance.
Solution Approach 2:
The electrode uses a composite multilayer structure combining Cr, Al/Ag, and Au materials. Each material contributes its superior properties: Cr for adhesion and ohmic contact, Al/Ag for low resistance, and Au for bonding. This composite approach achieves low contact resistance while maintaining manufacturing simplicity.
2Ease of manufacture
If Cr/Au electrodes are used for p-type and n-type nitride semiconductor layers, then the manufacturing process is simplified, but the light extraction efficiency decreases due to low reflectivity
Solution Approach 1:
The electrode structure applies local quality by using different materials at different locations and depths: Cr at the interface for contact, Al or Ag in the middle layer for high reflectivity where light extraction occurs, and Au at the top for bonding. This localized material optimization simultaneously achieves ease of manufacture and high light extraction efficiency.
Solution Approach 2:
The multilayer composite electrode combines Cr, Al/Ag, and Au to achieve both manufacturing simplicity and high reflectivity. The Al or Ag layer specifically provides the high reflectivity needed for light extraction, while the overall structure maintains the simple Cr/Au-based manufacturing process.
3Productivity
If Al or Ag is used in the compound layer, then the reflectivity increases for better light extraction, but the degradation and oxidation resistance decreases
Solution Approach 1:
The Cr layer acts as an intermediary between the nitride semiconductor and the Al/Ag compound layer, providing oxidation resistance at the semiconductor interface. The Au layer serves as an outer intermediary, protecting the Al/Ag layer from oxidation and environmental degradation. This allows Al/Ag to provide high reflectivity for light extraction while the Cr and Au layers protect against oxidation.
Solution Approach 2:
The electrode composite combines Al or Ag for high reflectivity with Cr and Au for oxidation resistance. The multilayer structure allows the Al/Ag layer to maximize light extraction efficiency while the Cr and Au layers provide protective functions, resolving the contradiction between reflectivity and oxidation resistance.
4Ease of manufacture
If the operational voltage increases due to high contact resistance, then the device can be manufactured with simple Cr/Au electrodes, but the heating value increases reducing reliability
Solution Approach 1:
The electrode is segmented into Cr, Al/Ag, and Au layers, where the Al or Ag layer specifically addresses the resistance issue by providing low resistivity. This segmentation allows the electrode to maintain manufacturing simplicity while reducing contact resistance and the resulting heating value.
Solution Approach 2:
The Cr/Al-Ag/Au composite electrode structure combines materials with complementary properties: Cr for contact, Al/Ag for low resistance (reducing heating), and Au for bonding. This composite approach reduces operational voltage and heating value while maintaining ease of manufacture.
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 solution reduces heating values, improves reliability, and increases light extraction efficiency by maintaining low ohmic contact resistance and high reflectivity, thereby enhancing the brightness and performance of nitride semiconductor LEDs.
Implementation Method 1
an ohmic contact layer which comes in an ohmic contact with the adjacent nitride semiconductor layer
Implementation Method 2
a compound layer containing aluminum or silver which has a function of reflecting the light emitted from an active layer
Implementation Method 3
a degradation preventing layer which has a function of preventing degradation and oxidation of the compound layer
Data Source
AI summary
A nitride semiconductor LED comprises a substrate; an n-type nitride semiconductor layer formed on the substrate; an active layer formed on a predetermined region of the n-type nitride semiconductor layer; a p-type nitride semiconductor layer formed on the active layer; a p-electrode formed on the p-type nitride semiconductor layer; and an n-electrode formed on the n-type nitride semiconductor layer in which the active layer is not formed. The p-electrode and n-electrode are formed to have such a multilayer structure that an ohmic contact layer, a compound layer containing aluminum or silver, and a degradation preventing layer are sequentially laminated.