Nitride LED Underlayer Structure for High-Indium Crystal Quality
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Solution Overview
Problem
Semiconductor light emitting devices using nitride semiconductors face challenges in achieving improved light emission characteristics due to lattice mismatch and resulting crystal defects when high indium content active layers are grown on GaN substrates, leading to degraded crystallinity.
Innovation Solution
A semiconductor light emitting device is designed with a nitride semiconductor substrate having a principal plane inclined from the c-plane, featuring a first underlayer with Alx2Inx1Ga(1-x1-x2)N and a second underlayer with Aly2Iny1Ga(1-y1-y2)N, both with dislocations along specific planes, forming a lattice-relaxed underlayer to improve the crystallinity of the active layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the indium content in the active layer is increased to achieve longer emission wavelength, then the emission wavelength is extended, but the lattice mismatch degree increases causing crystal defects and degraded crystallinity
Solution Approach 1:
The patent introduces an underlayer comprising AlGaInN with a specific lattice constant that serves as an intermediary between the GaN substrate and the high-indium-content active layer. This underlayer acts as a buffer that accommodates the lattice mismatch, preventing dislocation propagation from the substrate to the active layer while enabling high indium content growth for long wavelength emission.
Solution Approach 2:
The patent changes the lattice constant parameter of the underlayer by selecting AlGaInN composition with specific aluminum and indium contents. This parameter adjustment allows the underlayer to have a lattice constant that is lattice-relaxed, creating a transition zone that reduces the abrupt lattice mismatch between the GaN substrate and the high-indium active layer.
2Manufacturing precision
If a single underlayer is provided to reduce lattice mismatch, then some lattice relaxation is achieved, but dislocation propagation is not sufficiently suppressed
Solution Approach 1:
The patent divides the underlayer into multiple distinct layers: a first underlayer and a second underlayer, each with different AlGaInN compositions and lattice constants. This segmentation creates multiple transition zones that progressively accommodate lattice mismatch, with each layer serving as an intermediate step that suppresses dislocation propagation more effectively than a single underlayer.
Solution Approach 2:
The patent applies different AlGaInN compositions to different regions (layers) of the underlayer structure. The first underlayer has one specific composition optimized for interfacing with the GaN substrate, while the second underlayer has a different composition optimized for interfacing with the active layer. This local quality variation allows each layer to address specific lattice mismatch issues at its interface.
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 facilitates lattice relaxation and enhances the crystal quality of the active layer, resulting in superior light emission characteristics, particularly for devices emitting in the long wavelength band with high indium content.
Implementation Method 1
a layer with a lattice-relaxed lattice constant is provided between a GaN substrate and an optical device structure by spatially restricting misfit dislocation(s) around heterointerfaces
Data Source
AI summary
A semiconductor light emitting device of an embodiment of the present disclosure includes: a nitride semiconductor substrate having, as a principal plane, a plane inclined from a c-plane in an m-axis direction in a range from 60° to 90° both inclusive; an underlayer provided on the nitride semiconductor substrate and including a first layer and a second layer that are stacked on each other, the first layer including Alx2Inx1Ga(1-x1-x2)N (0<x1<1, 0≤x2<1) and having a dislocation along an intersection line of the principal plane of the nitride semiconductor substrate and a (1-100) plane, the second layer including Aly2Iny1Ga(1-y1-y2)N (0<y1<1, 0≤y2<1) and having a dislocation along an intersection line of the principal plane of the nitride semiconductor substrate and a (0001) plane; and a device layer including an active layer provided on the underlayer.