Buffer Structure for Semiconductor Light-Emitting Device
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Solution Overview
Problem
Semiconductor light-emitting devices with nitride-based semiconductor layers face performance degradation due to lattice constant and thermal expansion differences between substrates and layers, leading to increased dislocation density and cracking issues.
Innovation Solution
A buffer structure is introduced, comprising a nucleation layer, a dislocation-removing structure with specific material layers having different lattice constants, and a buffer layer to reduce dislocation density and tensile stress, including a first material layer with a rough surface and a second material layer with a lower lattice constant, and a buffer layer with a lattice constant between the semiconductor layers, to improve the light-emitting device's performance and prevent cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a nitride-based semiconductor layer is formed directly on a substrate, then the device structure is simple, but dislocation density increases and cracks occur due to lattice constant and thermal expansion differences
Solution Approach 1:
The buffer structure is divided into multiple functional layers: a nucleation layer for initial crystal formation, a first material layer with specific lattice constant, a second material layer with different lattice constant, and a buffer layer. This segmentation allows each layer to address specific dislocation issues progressively, reducing overall dislocation density while maintaining structural integrity
Solution Approach 2:
The buffer structure acts as an intermediary between the substrate and the nitride-based semiconductor layer. The multiple layers with progressively changing lattice constants serve as transition zones that mediate the stress and dislocation transmission, preventing direct contact between the mismatched substrate and semiconductor layer
2Ease of manufacture
If a nitride-based semiconductor layer is formed directly on a substrate, then the manufacturing process is simple, but cracks occur due to tensile stress from thermal expansion differences
Solution Approach 1:
The buffer structure is formed beforehand to cushion and absorb thermal expansion stresses before the nitride-based semiconductor layer is deposited. The multiple layers with different lattice constants and mechanical properties create a gradient that progressively absorbs stress, preventing crack formation in the final device structure
Solution Approach 2:
The buffer structure uses composite material layers with different lattice constants and mechanical properties. Each layer is carefully selected to provide both structural support and stress management, creating a composite system that resists thermal expansion-induced cracking while maintaining ease of manufacturing through sequential deposition
3Reliability
If the surface of the first material layer is made rough to reduce dislocation, then dislocation density decreases, but the interface quality with the second material layer deteriorates
Solution Approach 1:
The buffer structure employs local quality variations where different layers have different surface roughness characteristics optimized for their specific functions. The first material layer has a rough surface to scatter and terminate dislocations, while the second material layer provides a smoother interface for better epitaxial growth of the nitride-based semiconductor layer, with each layer's properties locally optimized for its role
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 proposed solution effectively reduces dislocation density, tensile stress, and the occurrence of cracks, enhancing the luminous efficiency and manufacturing yield of semiconductor light-emitting devices by optimizing the lattice constants and surface roughness of the material layers.
Implementation Method 1
the second material layer having a lattice constant different from a lattice constant of the first material layer
Implementation Method 2
a roughness of a surface of the first material layer in contact with the second material layer is higher
Implementation Method 3
a lattice constant of the buffer layer is between the lattice constant of the second material layer and a lattice constant of the first-type semiconductor layer
Data Source
AI summary
A semiconductor light-emitting device includes a buffer structure, a first-type semiconductor layer on the buffer structure, an active layer on the first-type semiconductor layer, and a second-type semiconductor layer on the active layer. The buffer structure includes a nucleation layer, a first dislocation-removing structure on the nucleation layer, and a buffer layer on the first dislocation-removing structure. The first dislocation-removing structure includes a first material layer on the nucleation layer and a second material layer on the first material layer. The second material layer has a lattice constant different from a lattice constant of the first material layer. A roughness of a top surface of the first material layer is higher than a roughness of a top surface of the nucleation layer and higher than a roughness of a top surface of the second material layer.