Vertical LED Through-Hole Mesa Layout for Current Spreading
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Solution Overview
Problem
Vertical light emitting diodes face challenges in achieving uniform current spreading and are vulnerable to moisture, which affects their luminous efficacy and reliability, especially when using nitride semiconductor layers that emit short wavelength UV light.
Innovation Solution
The design incorporates a support substrate, a first conductivity type semiconductor layer, an upper insulation layer, and a mesa structure with through-holes that expose the semiconductor layer, allowing for even current distribution and protection from moisture through a multi-layer insulation structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If electrode extensions are formed near edges of the epitaxial layers to evenly distribute current, then current spreading performance is improved, but light emission is blocked by the electrode extensions, deteriorating luminous efficacy
Solution Approach 1:
The patent transitions from planar current distribution to three-dimensional current distribution by forming through-holes through the mesa structure. This allows current to be injected from the top surface through the active layer to the first conductivity type semiconductor layer, enabling uniform current spreading without requiring lateral electrode extensions that would block light emission.
2Loss of energy
If the epitaxial layer surface is roughened to improve light extraction efficiency, then light extraction is enhanced, but the nitride semiconductor layer becomes vulnerable to moisture intrusion
Solution Approach 1:
The patent applies a multi-layer insulation structure consisting of a first insulation layer and a second insulation layer that covers the roughened surface of the first conductivity type semiconductor layer. This protective film structure prevents moisture intrusion while maintaining the light extraction benefits of the roughened surface.
Solution Approach 2:
The patent uses a composite insulation structure with multiple layers having different properties. The first insulation layer provides base protection, while the second insulation layer provides enhanced moisture barrier protection, creating a composite protective system that addresses both light extraction and moisture protection requirements.
Data Source
AI summary
A light-emitting diode includes a first conductive semiconductor layer, an upper insulating layer positioned on the first conductive semiconductor layer, a mesa including an active layer and a second conductive semiconductor layer and positioned under a certain region of the first conductive semiconductor layer, and first and second through-holes through which the first conductive semiconductor layer is exposed. The first through-holes are arranged in a region encompassed by the edge of the mesa. The second through-holes are arranged along the edge of the mesa so that some of the second through-holes are encompassed by the active layer and the second conductive semiconductor layer, respectively.