Semiconductor Light-Emitting Device Composition Gradient Layer
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Solution Overview
Problem
Semiconductor light-emitting devices face a reduction in light extraction efficiency due to lateral spreading of light when the distance between the emission layer and the reflective metal layer is increased, leading to a decrease in the quantity of light flux extracted from the front side.
Innovation Solution
The semiconductor light-emitting device incorporates a reflective metal layer with a composition gradient layer and a first contact layer of lower refractive index, which reduces carrier spread and enhances light extraction efficiency by suppressing lateral diffusion of light, thereby increasing the luminance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the distance between the emission layer and the reflective metal layer is increased, then the light extraction efficiency is improved, but the light quantity of the extracted light flux is reduced due to lateral spreading
Solution Approach 1:
The patent applies local quality by creating a composition gradient layer where the Al composition ratio varies continuously from the emission layer toward the contact layer. This gradient structure provides different optical properties at different depths: the upper portion maintains high light extraction efficiency, while the lower portion suppresses lateral light spreading, thus resolving the contradiction between extraction efficiency and light quantity preservation.
Solution Approach 2:
The patent changes the compositional parameter (Al composition ratio) continuously through the thickness of the contact layer to optimize optical performance. By adjusting the Al composition ratio from 0.5 in the emission layer to 0 in the lower contact layer, the refractive index gradient is controlled to minimize lateral light spreading while maintaining effective light extraction at the emission interface.
2Loss of energy
If a reflective metal layer is provided on the rear side of the emission layer, then light extraction efficiency is increased, but lateral spreading of reflected light reduces the extracted light quantity
Solution Approach 1:
The patent uses a composite structure consisting of the emission layer, composition gradient layer, and reflective metal layer. The composition gradient layer acts as an intermediate composite structure that bridges the optical mismatch between the emission layer and the reflective metal layer, enabling effective light extraction while controlling lateral spreading through its graded refractive index profile.
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 enhances light extraction efficiency and luminance by reducing the spread of light laterally, resulting in a higher output of light flux and improved performance in lighting devices.
Implementation Method 1
A light extraction efficiency of a semiconductor light-emitting device can be increased by providing a reflective metal layer on a rear side of an emission layer of the semiconductor light-emitting device such that light emitted from the emission layer toward a backside is reflected toward a front side.
Implementation Method 2
The semiconductor light-emitting device incorporates a reflective metal layer with a composition gradient layer and a first contact layer of lower refractive index, which reduces carrier spread and enhances light extraction efficiency by suppressing lateral diffusion of light
Data Source
AI summary
An embodiment has an emission layer, a first electrode having a reflective metal layer, an insulating layer, first and second conductivity type layers, and a second electrode. The insulating layer is provided on the first electrode and has an opening where a portion of the first electrode is provided. The first conductivity type layer is provided between the insulating layer and the emission layer and has bandgap energy larger than that of the emission layer. The second conductivity type layer is provided on the emission layer and has a current diffusion layer and a second contact layer. The second contact layer is not superimposed on the opening of the insulating layer, and a thickness of the current diffusion layer is larger than that of the first contact layer. The second electrode has a pad portion and a thin portion extends from the pad portion onto the second contact layer.