Pad Electrode Spacing in Semiconductor Light Emitting Devices
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Solution Overview
Problem
Current semiconductor light emitting devices face challenges in achieving high light extraction efficiency, particularly in applications requiring high output and efficiency, such as large-scale TV backlight units and vehicle headlamps, due to limitations in current spreading and light absorption by electrodes.
Innovation Solution
The semiconductor light emitting device incorporates a unique electrode structure with a current blocking layer, a reflective part, a transparent electrode layer, and a pad electrode part spaced apart from the transparent electrode layer, along with finger electrode parts and connection parts, to enhance current spreading and prevent light absorption, thereby improving light extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the pad electrode is placed in direct contact with the transparent electrode layer, then the electrical connection is simplified, but the light extraction efficiency deteriorates due to light absorption by the electrode
Solution Approach 1:
The electrode structure is segmented into separate functional components: the pad electrode part for electrical connection and the transparent electrode layer for light extraction. By spacing them apart, each component can optimize its function without compromising the other, resolving the contradiction between structural simplicity and light extraction efficiency.
Solution Approach 2:
The finger electrode parts serve as intermediary elements that connect the pad electrode to the transparent electrode layer without requiring direct contact between the pad electrode and transparent electrode. This intermediary structure maintains electrical connectivity while preserving light extraction efficiency.
2Productivity
If the transparent electrode layer is made larger to improve current spreading, then the current distribution improves, but the light absorption by the electrode increases, reducing light extraction efficiency
Solution Approach 1:
The electrode system is divided into the transparent electrode layer optimized for current spreading and the pad electrode optimized for electrical connection. This segmentation allows the transparent electrode layer to extend for better current distribution without proportionally increasing light absorption losses, as the pad electrode remains spaced apart.
Solution Approach 2:
Different regions of the electrode structure have different functions: the transparent electrode layer provides both current conduction and light transmission in the emission region, while the pad electrode provides robust electrical connection in the contact region. This local differentiation optimizes both current spreading and light extraction efficiency.
3Reliability
If the pad electrode covers the reflective part to improve electrical connection, then the electrical signal stability improves, but the light extraction efficiency deteriorates due to increased electrode absorption
Solution Approach 1:
The electrode structure separates the electrical connection function (pad electrode covering reflective part) from the light extraction function (transparent electrode layer). By spacing them apart, the pad electrode can fully cover the reflective part for stable electrical connection without compromising light extraction efficiency.
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 results in improved luminance values, with increased light extraction efficiency and reduced electrical signal concentration, enhancing the performance of semiconductor light emitting devices in high-output applications.
Implementation Method 1
a reflective part disposed on the current blocking layer
Implementation Method 2
a transparent electrode layer spaced apart from the reflective part, having an opening surrounding the reflective part, and disposed on the second conductivity type semiconductor layer
Data Source
AI summary
A semiconductor light emitting device includes a light emitting structure and first and second electrodes. The light emitting structure includes first and second conductivity type semiconductor layers and an active layer interposed therebetween. The first and second electrodes are electrically connected to the first and second conductivity type semiconductor layers. The second electrode includes a current blocking layer, a reflective part disposed on the current blocking layer, a transparent electrode layer disposed on the second conductivity type semiconductor layer, a pad electrode part disposed within a region of the current blocking layer, and at least one finger electrode part disposed at least in part on the transparent electrode layer. The transparent electrode layer can be spaced apart from the reflective part, and have an opening surrounding the reflective part. In some examples, the transparent electrode layer can further be spaced apart from the current blocking layer.