Nitride Semiconductor Substrate Off-Orientation Control
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Solution Overview
Problem
Conventional nitride semiconductor devices face issues such as low color purity, increased threshold current, and current collapse due to non-uniform crystal growth and imperfections in substrate surfaces, limiting their application in devices like liquid crystal displays and high-electron-mobility transistors.
Innovation Solution
A nitride semiconductor free-standing substrate with a surface inclined 0.03° to 1.0° from the C-plane and an off-orientation angle between 0.5° to 16° from the M-axis orientation, ensuring uniform step growth and minimizing regions with off-orientation displacement, is used to improve crystal linearity and device performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a substrate with large off-orientation (conventional approach) is used to achieve step-flow mode growth, then crystal growth uniformity is improved, but emission color purity deteriorates due to increased half-value width
Solution Approach 1:
The invention changes the off-orientation parameter from the conventional large angle (several degrees from M-axis) to a small angle (0.5° to 16° from M-axis). This parameter change enables simultaneous achievement of uniform step-flow growth and high emission color purity by optimizing the balance between step linearity and emission spectrum characteristics.
2Manufacturing precision
If conventional substrates with M-axis orientation are used, then step linearity is improved for crystal growth, but device performance deteriorates due to current collapse and high threshold current
Solution Approach 1:
The invention modifies the orientation parameter by displacing it from the conventional M-axis orientation by a small angle (0.5° to 16°). This creates an optimized orientation that maintains sufficient step linearity for uniform crystal growth while simultaneously improving device reliability by suppressing current collapse and reducing threshold current in laser diodes.
3Ease of manufacture
If hetero-substrates like sapphire or SiC are used, then crystal growth is enabled, but device characteristics deteriorate due to non-uniformity in crystal growth across the substrate surface
Solution Approach 1:
The invention creates a substrate with locally optimized surface properties by controlling the off-orientation angle uniformly across the entire substrate surface. This ensures that each region of the substrate provides consistent step-flow growth conditions, eliminating the non-uniformity problem that occurs with conventional hetero-substrates and enabling uniform device characteristics across the wafer.
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 enables the growth of high-quality nitride semiconductor layers with improved emission purity, reduced threshold currents, and suppressed current collapse, enhancing the characteristics of nitride semiconductor light-emitting and electronic devices.
Implementation Method 1
atoms supplied onto the substrate surface are likely to be incorporated into the steps when growing a nitride semiconductor crystal on the substrate, which results in so-called step-flow mode growth, and a good quality crystal with few defects can be obtained
Data Source
AI summary
A nitride semiconductor free-standing substrate includes a surface inclined in a range of 0.03° to 1.0° from a C-plane, and an off-orientation that an angle defined between a C-axis and a tangent at each point on a whole surface of the substrate becomes maximum is displaced in a range of 0.5° to 16° from a particular M-axis orientation of six-fold symmetry M-axis orientations. The substrate does not include a region of −0.5°<φ<+0.5° on the surface, where φ represents a displacement angle of the off-orientation on a surface of the substrate from the particular M-axis orientation.