GaN LED Intermediate Layers for Radiative Efficiency
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Solution Overview
Problem
Current LED manufacturing techniques using GaN/InGaN semiconductors face challenges in achieving high radiative efficiency due to low hole current mobility and high indium content, which leads to lattice stress, defects, and reduced crystalline quality, limiting the efficiency of LEDs, especially at higher current densities.
Innovation Solution
Incorporating intermediate layers with a larger bandgap than the barrier layers within the active zone of LEDs, composed of InGaN, to relax stress and improve crystalline quality, allowing for higher indium concentrations and enhanced radiative efficiency by promoting better hole circulation and balance between electrons and holes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the proportion of indium in InGaN is increased to enhance radiative efficiency, then the radiative efficiency improves, but lattice stress and defects increase due to the large difference in lattice parameter between GaN and InN
Solution Approach 1:
An intermediate layer comprising AlInGaN is inserted between the GaN buffer layer and the InGaN active zone. This intermediate layer acts as a mediator that gradually transitions the lattice structure, reducing the abrupt lattice mismatch between GaN and high-indium-content InGaN. The intermediate layer has a composition gradient with increasing indium content from bottom to top, which progressively accommodates the lattice expansion, thereby reducing dislocation density and maintaining crystalline quality while enabling higher indium content in the active zone for improved radiative efficiency.
2Ease of operation
If the thickness of InGaN barrier layers is increased to facilitate hole circulation, then hole current improves, but the crystalline quality deteriorates due to stress and defect formation
Solution Approach 1:
The barrier layers are designed with spatially varying indium content, creating local compositional gradients. The indium concentration increases from the bottom interface toward the top of each barrier layer, which locally accommodates lattice stress and reduces dislocation formation. This local quality variation allows the barrier layers to maintain adequate thickness for hole circulation while preserving overall crystalline quality by distributing stress locally rather than uniformly.
3Power
If high current density is applied to increase LED power output, then the power increases, but radiative efficiency drops rapidly due to LED droop
Solution Approach 1:
The LED structure employs systematic parameter changes in the composition gradient of the intermediate layer and barrier layers. The indium content is optimized to vary spatially, creating a gradient that modifies the conduction band profile and enhances hole injection efficiency. This parameter optimization ensures that at high current densities, holes are efficiently supplied to the active zone, maintaining high radiative efficiency even at elevated power outputs by reducing the imbalance between electron and hole injection rates that causes LED droop.
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 introduction of intermediate layers increases radiative efficiency and reduces non-radiative recombination centers, leading to improved optical quality and efficiency across a wider range of current densities, particularly beneficial for LEDs emitting in the green and red spectrum.
Implementation Method 1
the reduction in lattice stress between InyGa1-yN barrier layers and InXGa1-XN emissive layers, where X > Y
Implementation Method 2
the charge carriers (electrons and holes) can recombine radiatively in the p-n junction depletion zone
Implementation Method 3
an active zone made up of several quantum wells formed from emissive layers of InGaN each placed between two barrier layers of GaN
Data Source
Figure 1~2
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Figure 5~6
AI summary
Light-emitting diode (100) comprising: first and second semiconductor layers (102, 104) respectively doped n-type and p-type, forming a p-n junction; an active zone (105) placed between the first and second layers, comprising an InXGa1-XN emitting layer (106) able to form a quantum well, and two InYGa1-YN, 0 < Y < X, barrier layers (108) between which the emitting layer is placed; an intermediate layer (114), which is placed either in the barrier layer located between the emitting layer and the first layer and portions of which are then on either side of the intermediate layer, or placed between said barrier layer and the emitting layer, the intermediate layer including a III-N semiconductor of bandgap wider than that of said barrier layer; and wherein: the second layer includes GaN or InWGa1-WN, 0 < W < Y, and the first layer In VGa1-VN, V > W > 0.