LED Chip Current-Spreading Layer Thickness Variation
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Solution Overview
Problem
Conventional light-emitting diodes face challenges in achieving uniform brightness and maintaining suitable electrical properties due to the obstruction caused by opening patterns in the current-spreading layer, which affects light extraction efficiency and driving voltage.
Innovation Solution
A light-emitting diode chip design featuring a current-spreading layer with varying thickness portions, where the second portion's vertical projection surrounds the first electrode's projection, and an optional recess on the current-spreading layer to enhance light emission angle, improving light extraction efficiency while maintaining current-spreading efficiency within a suitable range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If an opening pattern that penetrates through the current-spreading layer is formed to increase light emission angle, then light extraction efficiency is improved, but current-spreading is obstructed resulting in non-uniform brightness and degraded electrical properties
Solution Approach 1:
The current-spreading layer is designed with spatially varying thickness: a first portion with greater thickness for optimal current distribution, and a second portion with lesser thickness to allow light extraction. This local differentiation enables the same layer to fulfill both current-spreading and light extraction functions without requiring opening patterns that would obstruct current flow.
Solution Approach 2:
Instead of creating openings in the planar current-spreading layer (2D approach), the invention utilizes the thickness dimension (3D approach) by forming a current-spreading layer with varying thickness. The second portion's vertical projection surrounds the first electrode's projection, creating a stepped structure that allows light extraction through the thinner region while maintaining current-spreading integrity through the thicker region.
2Loss of energy
If the current-spreading layer is made thinner to improve light extraction, then light emission angle increases, but current-spreading efficiency deteriorates
Solution Approach 1:
The current-spreading layer employs local quality variation with a first portion having greater thickness for current-spreading and a second portion having lesser thickness for light extraction. This resolves the contradiction by assigning different thickness characteristics to different functional regions of the same layer.
Solution Approach 2:
The current-spreading layer is segmented into multiple portions with different thickness characteristics. The first portion (thicker) handles current distribution while the second portion (thinner) facilitates light extraction, allowing both functions to operate optimally without compromising either.
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 design enhances brightness and luminous efficiency of light-emitting diodes by 0.5-1.1% while keeping the driving voltage variation minimal, improving overall performance compared to conventional designs.
Implementation Method 1
a current-spreading layer is formed on the second-type semiconductor layer... such that the current can be uniformly transferred to the p-type semiconductor layer and the p-n junction
Implementation Method 2
the electrons combine with the holes at the p-n junction. As a result, energy is released and therefore a luminescence phenomenon happens
Implementation Method 3
an opening pattern that penetrates through the current-spreading layer may be formed to increase the light emission angle of the light generated by the active layer
Data Source
AI summary
A light-emitting diode (LED) chip is disclosed. The LED chip includes a substrate and a LED stack on the substrate. The LED stack includes a first-type semiconductor layer, an active layer covering a portion and exposing another portion of the first-type semiconductor layer, and a second-type semiconductor layer on the active layer. A current spreading layer is formed on the second-type semiconductor layer. A first electrode is formed on the exposed portion of the first-type semiconductor layer, and a second electrode is formed on the current spreading layer. The current spreading layer includes a first portion having a first thickness and a second portion having a second thickness. A vertical projection of the second portion onto the first-type semiconductor layer surrounds a vertical projection of a portion of the first electrode onto the first-type semiconductor layer. The first thickness is greater than the second thickness.