Nitride Semiconductor Layer Composition Gradient for Lattice Mismatch
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Solution Overview
Problem
Conventional nitride semiconductor laser devices face issues such as substrate warping and cracking due to lattice constant differences, leading to reduced yield and deteriorated device characteristics, and strain in the active layer resulting in decreased luminous efficiency.
Innovation Solution
A semiconductor device structure where the nitride semiconductor layer is formed with a higher composition ratio of the lightest group III element than the substrate, reducing lattice constant differences and enhancing bonding strength, which suppresses substrate warping, cracking, and dislocation, thereby improving device characteristics and luminous efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If AlGaN cladding layers with the same Al composition ratio as the substrate are used, then substrate warping and cracking are suppressed, but absorption power of Al, Ga, and N decreases leading to pit and dislocation formation
Solution Approach 1:
The patent changes the Al composition ratio parameter of the AlGaN cladding layer to be higher than that of the substrate. This parameter change increases absorption power of Al, Ga, and N, suppressing pit and dislocation formation, while the gradient structure manages substrate stress.
Solution Approach 2:
The patent creates a gradient in Al composition ratio from the substrate interface toward the active layer. The AlGaN cladding layer has locally higher Al composition than the substrate, optimizing absorption power in the region where it is most needed while managing overall substrate stress.
2Device complexity
If InGaN active layer is sandwiched by AlGaN cladding layers occupying most of the thickness, then device structure is formed, but strain occurs in the active layer causing reduced luminous efficiency
Solution Approach 1:
The patent adjusts the Al composition ratio parameter of the AlGaN cladding layer to be higher than the substrate, which modifies the lattice constant and reduces strain in the InGaN active layer, thereby improving luminous efficiency while maintaining the layered structure.
Solution Approach 2:
The patent creates a gradient in Al composition ratio that is localized in the AlGaN cladding layer. This local quality change reduces lattice mismatch strain specifically at the interfaces with the active layer, improving luminous efficiency without compromising the overall 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 proposed structure effectively suppresses substrate warping and cracking, reduces dislocation, and enhances luminous efficiency by compensating for strain in the active layer, leading to improved semiconductor device performance.
Implementation Method 1
a lattice constant difference between the GaN substrate and each of the AlGaN cladding layers that occupy most of the thickness of the light-emitting device structure
Implementation Method 2
A decrease, however, in absorption power of Al, Ga, and N which are constituent elements of the nitride semiconductor layer growing on the AlGaN substrate leads to a drawback
Implementation Method 3
strain occurs in the active layer due to the lattice constant difference between the AlGaN cladding layer and the InGaN substrate
Data Source
AI summary
A semiconductor device includes a semiconductor substrate formed of at least two kinds of group III elements and nitrogen, an active layer formed on the semiconductor substrate, and a nitride semiconductor layer formed on a surface of the semiconductor substrate and formed between the semiconductor substrate and the active layer. The nitride semiconductor layer is formed of the same constituent elements of the semiconductor substrate. A composition ratio of the lightest element among the group III elements of the nitride semiconductor layer is higher than a composition ratio of the corresponding element of the semiconductor substrate.