Vertical LED Mesa Through-Hole Layout for Uniform 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 emitting short wavelength UV light.
Innovation Solution
A vertical light emitting diode structure is designed with a support substrate, a first conductivity type semiconductor layer, an upper insulation layer, and a mesa with through-holes that expose the semiconductor layer, allowing for even current distribution and protection from moisture using a multi-layer insulation layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a cathode pad and electrode extension are disposed on the epitaxial layer to assist current spreading, then current spreading performance is improved, but light emission is blocked and luminous efficacy deteriorates
Solution Approach 1:
The patent extracts the electrode extension from the light emission region by positioning it on the support substrate rather than on the epitaxial layer. The cathode pad remains on the epitaxial layer but is minimized in size. This separation removes the blocking effect from the light path while maintaining current spreading functionality through the electrode extension on the substrate.
Solution Approach 2:
The patent transitions the electrode extension from a two-dimensional planar structure on the epitaxial layer to a three-dimensional structure that extends vertically from the support substrate up to the epitaxial layer. This dimensional change allows current spreading to occur through the vertical dimension without blocking horizontal light emission from the epitaxial layer.
2Loss of energy
If the epitaxial layer surface is roughened to improve light extraction efficiency, then light extraction is enhanced, but the structure becomes more vulnerable to moisture intrusion
Solution Approach 1:
The patent applies a multi-layer protective coating system consisting of different materials (e.g., aluminum oxide layer and silicon oxide layer) on the roughened epitaxial layer surface. This composite structure combines the light extraction benefits of surface roughening with the moisture barrier properties of the protective coating layers.
Solution Approach 2:
The patent creates a protective environment around the roughened epitaxial layer by applying impermeable coating layers that effectively create an inert barrier against moisture. This protective atmosphere prevents harmful moisture interaction with the vulnerable roughened semiconductor surface.
3Temperature
If a support substrate with higher thermal conductivity than sapphire is used, then heat dissipation performance is improved, but device structure becomes more complex
Solution Approach 1:
The patent uses a support substrate that serves multiple functions simultaneously: it provides mechanical support for the epitaxial layers, acts as a thermal management component due to its high thermal conductivity, and functions as an electrical component by accommodating the electrode extension. This multi-functionality reduces overall device complexity despite the enhanced thermal performance requirements.
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 solution enables more uniform current spreading and improved reliability by preventing moisture intrusion, enhancing the light emitting diode's luminous efficacy and durability.
Implementation Method 1
a first electrode disposed between the second conductivity type semiconductor layer and the support substrate and electrically connected to the first conductivity type semiconductor layer through the first through-holes
Implementation Method 2
a reflective metal layer may be formed between the support substrate and the semiconductor layers to reflect light traveling towards the support substrate, thereby improving light extraction efficiency
Implementation Method 3
the vertical light emitting diode can improve light extraction efficiency through a roughened surface of an epitaxial layer (n-type semiconductor layer) through which light is emitted
Implementation Method 4
The roughened surface of the epitaxial layer need protection from an external environment. In particular, as a light emitting diode, emitting short wavelength UV light including a nitride epitaxial layer containing Al, such as AlGaN, is vulnerable to moisture, there is a need for protection of the light emitting diode
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.