LED Chip Electrode Pad Design for Uniform Current Spreading
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Solution Overview
Problem
GaN-based light emitting diodes (LEDs) face issues with reduced light emitting area and efficiency due to the formation of electrode pads and extensions, which cause current crowding and optical loss, leading to deterioration in light emitting efficiency and external quantum efficiency, especially at high currents.
Innovation Solution
The LED chip design includes a semiconductor stack with electrode pads and extensions connected through through-holes or mesa structures, and the use of insulation and reflective layers to prevent current crowding and optical loss, allowing for uniform current spreading and reduced absorption of light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If electrode pads and extensions are formed on the semiconductor layer to assist current spreading, then current spreading is improved, but light emitting area is reduced
Solution Approach 1:
An insulation layer is introduced as an intermediary between the electrode pad and the semiconductor layer. This insulation layer allows the electrode pad to be positioned above the light emitting area without directly contacting the semiconductor layer, thereby maintaining current spreading functionality while preventing the electrode pad from occupying the light emitting area.
2Ease of operation
If electrode pads and extensions are formed to enhance current spreading, then current distribution is improved, but optical loss increases due to light absorption by metal electrodes
Solution Approach 1:
The insulation layer acts as an intermediary that optically isolates the light-emitting region from the metal electrode pad. This prevents direct absorption of generated light by the metal electrode, reducing optical loss while preserving the current spreading function of the electrode extensions.
3Ease of operation
If electrode extensions are used to improve current spreading, then current distribution is enhanced, but current crowding still occurs at regions near the electrode extensions
Solution Approach 1:
The electrode pad is positioned in a different spatial dimension (above the semiconductor layer rather than on it), and the insulation layer creates a vertical separation. This dimensional change allows current to spread more uniformly through the insulation layer and into the semiconductor layer, reducing current crowding at the interface.
Data Source
AI summary
Disclosed herein in an LED chip including electrode pads. The LED chip includes a semiconductor stack including a first conductive type semiconductor layer, a second conductive type semiconductor layer on the first conductive type semiconductor layer, and an active layer interposed between the first conductive type semiconductor layer and the second conductive type semiconductor layer, a first electrode pad located on the second conductive type semiconductor layer opposite to the second conductive type semiconductor layer; a first electrode extension extending from the first electrode pad and connected to the first conductive type semiconductor layer; a second electrode pad electrically connected to the second conductive type semiconductor layer; and an insulation layer interposed between the first electrode pad and the second conductive type semiconductor layer. The LED chip includes the first electrode pad on the second conductive type semiconductor layer, thereby increasing a light emitting area.