Nitride Semiconductor Electrode Reflectivity via Segmented Metal Layers
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Solution Overview
Problem
Nitride group semiconductor light emitting devices face challenges with low reflectivity of traditional pad electrodes, leading to reduced light output and poor adhesive strength of alloy electrodes, making them impractical for use.
Innovation Solution
A pad electrode structure comprising multiple metal layers, including a first metal layer with Cr and a reflectivity-enhancing material like Rh, and a second metal layer with Pt, optimized for thickness and composition to achieve high reflectivity and adhesive strength, while minimizing light absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a traditional pad electrode structure (Cr/Au or Cr/Pt/Au) is used, then adhesive strength is achieved, but light reflectivity is low
Solution Approach 1:
The pad electrode is divided into multiple functional layers: a Cr-containing layer for adhesion, a Rh-containing layer for high reflectivity, and a Pt-containing layer for oxidation resistance. Each layer performs its specific function, resolving the contradiction between adhesive strength and light reflectivity.
Solution Approach 2:
The pad electrode uses a composite structure combining Cr, Rh, and Pt in specific layers. This composite material approach allows the electrode to simultaneously achieve good adhesion (Cr), high reflectivity (Rh), and oxidation resistance (Pt), resolving the contradiction between adhesive strength and light reflectivity.
2Reliability
If alloy electrodes are used to improve adhesive strength, then bonding is enhanced, but light absorption increases
Solution Approach 1:
The electrode structure assigns different properties to different layers: the Cr layer provides local bonding quality, the Rh layer provides local high reflectivity (low absorption), and the Pt layer provides oxidation resistance. This local quality differentiation resolves the contradiction between bonding strength and light absorption.
Solution Approach 2:
Instead of using alloy electrodes that provide bonding but cause light absorption, the invention uses a multi-layer structure where the Rh layer converts the harmful absorption into beneficial reflection, while the Cr layer provides the necessary bonding. This transforms the harmful effect into a beneficial one.
3Reliability
If the first metal layer thickness is increased to improve adhesion, then bonding is enhanced, but light reflectivity decreases
Solution Approach 1:
The electrode is segmented into layers with the Cr layer (5-20 nm) providing adhesion and the Rh layer (20-50 nm) providing reflectivity. By separating these functions into different layers rather than increasing the Cr layer thickness, both adhesive strength and light reflectivity are optimized.
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 proposed electrode structure significantly improves light reflectivity and adhesive strength, enhancing the light outgoing efficiency and reliability of nitride group semiconductor light emitting devices.
Implementation Method 1
the first metal layer contains Cr, and a first metal material... the first metal material is Rh... the thickness of said first metal layer is smaller than 10 nm
Implementation Method 2
an electrode structure... which includes a plurality of deposited metal layers
Data Source
Figure 1~2
Figure 3
Figure 4~5
AI summary
ISSUE An electrode is provided which has improved reflectivity for improvement of light outgoing efficiency. MEANS FOR SOLUTION A nitride group semiconductor light emitting device includes a nitride group semiconductor layer, and an electrode structure. The electrode structure is arranged on or above the semiconductor layer, and includes a plurality of deposited metal layers. The plurality of deposited metal layers of the electrode structure includes first and second and metal layers. The first metal layer is arranged on the semiconductor layer side. The second metal layer is arranged on or above the first metal layer. The first metal layer contains Cr, and a first metal material. The first metal material has a reflectivity higher than Cr at the light emission peak wavelength of the light emitting device. According to this construction, the first metal layer can have a higher reflectivity as compared with the case where the first metal layer is only formed of Cr, but can keep tight contact with the semiconductor layer.