Optical Semiconductor Electrode Stress Distribution
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Solution Overview
Problem
Semiconductor laser devices experience crystal destruction due to stress developed in the electrode layer, which affects the distribution of electrons and holes, leading to increased current density and potential crystal damage.
Innovation Solution
The optical semiconductor device features an electrode layer with a two-stage structure, utilizing Ti/Pt and Au layers to distribute stress evenly, preventing concentration at the electrode ends and maintaining reliability through stress relaxation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a continuous electrode layer is formed on the semiconductor substrate, then electrical connection is achieved, but stress concentration occurs at the electrode ends causing crystal destruction
Solution Approach 1:
The electrode layer is divided into multiple discrete electrode regions rather than forming a continuous layer. Each electrode region is separated by spacing, which prevents stress from concentrating at continuous electrode ends. The segmentation distributes the stress across multiple isolated points, eliminating the harmful stress concentration that would otherwise destroy the crystal structure.
2Strength
If electrode layer thickness is increased to improve adhesion, then bonding strength increases, but stress magnitude increases causing greater distortion
Solution Approach 1:
Different regions of the electrode structure have different properties. The electrode layers are made with specific thicknesses optimized for local adhesion requirements rather than uniform thickness throughout. The spacing between electrode regions creates local variations in stress distribution, allowing adequate adhesion where electrodes contact the substrate while minimizing overall stress magnitude through the spaced configuration.
3Reliability
If reflective layers are added to control laser output, then optical performance is improved, but device complexity increases
Solution Approach 1:
The electrode layers serve multiple functions simultaneously: they provide electrical connection, act as reflective layers for laser output control, and function as stress distribution elements through their spaced configuration. By making the electrode structure multi-functional, additional components are avoided, and device complexity is reduced while maintaining reliable laser output control.
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 significantly reduces stress concentration, enhancing the reliability of the semiconductor laser device by ensuring even stress distribution, thereby preventing crystal destruction and maintaining performance.
Implementation Method 1
Ti is for securing adhesion with a substrate
Implementation Method 2
Pt is for stopping the diffusion of Au into the substrate
Implementation Method 3
Au is for a current layer and wire bonding
Implementation Method 4
The stress becomes maximum at the electrode layer ends 20b which are discontinuous points. The thickness of the InP substrate 10 whose rear surface has been polished is 90 μm which is thin. On the other hand, the stress of the electrode layer 20 is a tension stress of GPa order.
Implementation Method 5
An electrode is formed on the active surface side, and is connected to the active surface, has a step configuration at its entire outer periphery
Data Source
Figure 1~2
Figure 3~4
Figure 5A~5E
AI summary
In an optical semiconductor device that emits or receives light substantially perpendicularly to or in parallel to an active surface formed on a semiconductor substrate, the optical semiconductor device, an electrode (20) that is formed on the active surface side and connected to the active surface is stepped or tapered at an end of the electrode. The electrode of the optical semiconductor device is formed of three layers including an adhesive layer, a diffusion prevention layer, and an Au layer, and the stepped configuration or the taped configuration is formed by a difference of the thickness of the Au layer (20a) or the thickness of the adhesive layer/diffusion prevention layer/Au layer.