AlInGaN Layer Stack Structure for Lower GaN Dislocation Density
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Solution Overview
Problem
The high density of threading dislocations in GaN-based compound semiconductor layers leads to deteriorated device characteristics, including leak current generation and reduced luminous efficiency in light-emitting devices.
Innovation Solution
A compound semiconductor layer stack is formed with a first layer having a forward tapered sloped surface and a flat top surface, followed by a second layer grown on both the top and sloped surfaces of the first layer, optimizing the thickness ratios and growth conditions to reduce dislocation density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a GaN-based compound semiconductor layer is grown on a heterogeneous substrate, then the device can be manufactured, but threading dislocation density increases leading to deteriorated device characteristics
Solution Approach 1:
The patent introduces an AlInGaN intermediate layer between the GaN-based compound semiconductor layer and the heterogeneous substrate. This intermediate layer acts as a mediator that reduces lattice mismatch and thermal stress, thereby suppressing threading dislocation generation while enabling manufacturing on heterogeneous substrates. The intermediate layer has compositional gradient (varying In and Al contents) to progressively bridge the lattice constant difference between substrate and GaN layer.
2Productivity
If threading dislocation density is high, then manufacturing is simpler, but leak current increases and luminous efficiency decreases
Solution Approach 1:
The AlInGaN intermediate layer with compositional gradient serves as an intermediary structure that suppresses threading dislocation propagation. By controlling the In and Al content progression through the intermediate layer, the patent reduces dislocation density without complicating the manufacturing process, thereby maintaining productivity while improving luminous efficiency.
3Device complexity
If threading dislocation extends to functional layers, then device manufacturing is easier, but device reliability deteriorates
Solution Approach 1:
The patent segments the semiconductor layer structure into distinct regions: heterogeneous substrate, AlInGaN intermediate layer with compositional gradient, and GaN-based compound semiconductor layer. This segmentation isolates the threading dislocations generated at the substrate interface within the intermediate layer, preventing their extension into the functional GaN layer while maintaining overall structural simplicity.
4Reliability
If insulating layer mask technique is used to reduce threading dislocation, then dislocation density decreases, but manufacturing time increases and flatness is difficult to achieve
Solution Approach 1:
Instead of using an insulating layer mask that requires additional processing steps, the patent changes the compositional parameters of the semiconductor layer itself by introducing an AlInGaN intermediate layer with gradient composition. This parameter change approach reduces threading dislocation density through material composition control rather than geometric masking, thereby reducing manufacturing time and naturally achieving flat surfaces.
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 approach significantly reduces the threading dislocation density, leading to improved device reliability, reduced leak current, and enhanced luminous efficiency in light-emitting devices.
Implementation Method 1
a second layer which is grown on both the top surface and the sloped surface of the first layer
Data Source
Figure 1
Figure 2A~2D
Figure 3
AI summary
A compound semiconductor layer stack includes: a first layer 11 being formed on a base 14 and including an island-shaped Alx1Iny1Ga(1-x1-y1)N; a second layer 12 being formed on the first layer 11 and including Alx2Iny2Ga(1-x2-y2)N; and a third layer 13 being formed on an entire surface including a top of the second layer 12, the third layer 13 including Alx3Ga(1-x3)N (provided that the following hold true: 0 ≤ x1 < 1; 0 ≤ x2 < 1; 0 ≤ x3 < 1; 0 ≤ y1 < 1; and 0 < y2 < 1), and the third layer 13 has a top surface 13A that is flat.