Light Emitting Device Second Electrode Layer Bandgap Engineering
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Solution Overview
Problem
Conventional light emitting devices suffer from low light extraction efficiency due to light absorption in the p-type GaN layer, which reduces the overall emission of light from the multi quantum well layer.
Innovation Solution
The implementation of a second electrode layer with an energy band gap higher than the active layer, made of materials like AlN or BN, which allows light to pass through or be reflected instead of being absorbed, thereby improving light extraction efficiency. This layer also functions as an electron blocking layer and eliminates the need for a separate electron blocking layer, and can include dopants like oxygen and carbon to enhance carrier concentration and electric properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a p-type GaN layer is used as the second electrode layer, then good electrical contact and hole injection are achieved, but light emitted from the active layer is absorbed, reducing light extraction efficiency
Solution Approach 1:
The patent divides the second electrode layer into multiple sub-layers with different functions: a lower sub-layer for electrical contact and hole injection, and an upper sub-layer for light transmission. This segmentation allows each sub-layer to optimize its specific function without compromising the other.
Solution Approach 2:
Different regions of the second electrode layer are given different material compositions and properties. The lower region near the active layer has properties optimized for electrical contact, while the upper region has properties optimized for light transmission, creating local quality variations that resolve the contradiction.
2Reliability
If the thickness of the second electrode layer is increased to improve electrical properties, then carrier concentration increases, but light absorption increases, reducing light extraction efficiency
Solution Approach 1:
The second electrode layer is segmented into multiple thin sub-layers instead of one thick layer. This allows the total thickness to be sufficient for electrical properties while each individual sub-layer remains thin enough to transmit light effectively.
Solution Approach 2:
The patent changes the material composition parameter of the second electrode layer, using materials with wider bandgap than the active layer. This parameter change allows the layer to maintain electrical functionality while reducing light absorption across the emission spectrum.
3Reliability
If a separate electron blocking layer is added to prevent electron leakage, then device reliability improves, but device complexity and manufacturing steps increase
Solution Approach 1:
The patent merges the electron blocking function with the second electrode layer by incorporating electron blocking materials into the electrode layer structure. This combining eliminates the need for a separate electron blocking layer while maintaining both electron blocking and electrical contact functions.
Solution Approach 2:
The second electrode layer is designed to perform multiple functions simultaneously: electrical contact, hole injection, electron blocking, and light transmission. This multi-functionality reduces the total number of layers needed in the device structure.
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 significantly enhances light extraction efficiency by allowing more light to escape into air, improving luminous efficacy, and reduces the thickness and activation energy of the second electrode layer, leading to improved electric properties and reduced absorption of emitted light.
Implementation Method 1
light directed toward the p-type GaN layer 28 is absorbed in the p-type GaN layer 28 and thus does not contribute to light emission of the light emitting device
Implementation Method 2
a second electrode layer which contacts the second conductive type semiconductor layer and has an energy band gap higher than an energy band gap of the active layer
Implementation Method 3
The MQW layer 24 emits light having an energy determined by an inherent energy band of a material constituting an active layer 24, based on recombination between holes injected through the p-type AlGaN layer 26 and electrons injected through the n-type AlGaN layer 22
Data Source
AI summary
A light emitting device includes a substrate and a light emitting structure including a first conductive type semiconductor layer, an active layer and a second conductive type semiconductor layer provided in a first direction on the substrate. A first electrode layer is provided over the first conductive type semiconductor layer, and a second electrode layer is provided in a second direction over the second conductive type semiconductor layer. The second electrode layer has an energy band gap wider than an energy band gap of the active layer.