GaN Composite Substrate with Metal Oxide Protective Layer
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Solution Overview
Problem
Current semiconductor substrates, particularly those made of gallium nitride, face challenges with high dislocation density due to heteroepitaxial growth on non-native substrates, leading to defective device performance, and existing methods like hydride vapor phase epitaxy struggle to reduce dislocation density below 10^5 cm^-2, while ammonothermal growth improves this but requires a high-quality interface for optimal performance.
Innovation Solution
A composite substrate with a metal oxide layer on top of a low-dislocation group III nitride layer, where the metal oxide acts as a protective layer until device formation, and can be removed through in-situ etching, ensuring a smooth interface and preventing defect propagation by selectively staying at dislocation termination points.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If heteroepitaxial growth is used on sapphire or silicon carbide substrates, then device fabrication can proceed with available substrates, but high dislocation density and defective performance result
Solution Approach 1:
The substrate structure is segmented into multiple functional layers: a support substrate (sapphire or silicon carbide) providing mechanical strength and availability, and a separate low-dislocation GaN buffer layer grown on top, which provides the high-quality crystalline interface needed for device performance. This segmentation allows each layer to fulfill its specific function independently.
Solution Approach 2:
A low-dislocation GaN buffer layer acts as an intermediary between the heteroepitaxial substrate and the device structure. This intermediate layer mediates the lattice mismatch and dislocation propagation, allowing the device to achieve low dislocation density despite being grown on a heterogeneous substrate.
2Reliability
If ammonothermal growth is used to reduce dislocation density, then low dislocation density can be achieved, but a high-quality interface is required which complicates the process
Solution Approach 1:
The low-dislocation GaN buffer layer is grown in advance using ammonothermal growth before device fabrication begins. This preliminary action creates a pre-prepared high-quality interface that eliminates the need for complex in-situ interface preparation steps during device fabrication, simplifying the overall process.
Solution Approach 2:
The invention changes the growth parameters and methodology by using ammonothermal growth at controlled temperatures and pressures to grow the buffer layer with extremely low dislocation density. This parameter change enables achievement of low dislocation density without requiring complex interface preparation during subsequent device fabrication.
3Manufacturing precision
If a protective layer is added to protect the substrate surface, then surface quality is improved, but additional processing steps are required
Solution Approach 1:
A metal oxide layer is introduced as an intermediary protective layer on top of the low-dislocation GaN buffer. This layer protects the buffer surface during handling and fabrication while being removable through in-situ etching, thereby adding minimal complexity while significantly improving surface quality protection.
Solution Approach 2:
The metal oxide protective layer is temporarily added to protect the substrate surface during fabrication, then deliberately removed through in-situ etching to expose the high-quality GaN surface for device growth. This temporary addition and subsequent removal allows surface protection without permanent complexity.
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 provides a high-quality surface for device fabrication, reducing dislocation density and enhancing the reliability and performance of optoelectronic and electronic devices by protecting the substrate surface and allowing for precise control of the interface quality.
Implementation Method 1
a metal oxide layer on top of a low-dislocation group III nitride layer
Implementation Method 2
can be removed through in-situ etching
Data Source
AI summary
The present invention discloses a novel composite substrate which solves the problem associated with the quality of substrate surface. The composite substrate has at least two layers comprising the first layer composed of GaxAlyIn1-x-yN (0≦x≦1, 0≦x+y≦1) and the second layer composed of metal oxide wherein the second layer can be removed with in-situ etching at elevated temperature. The metal oxide layer is designed to act as a protective layer of the first layer until the fabrication of devices. The metal oxide layer is designed so that it can be removed in a fabrication reactor of the devices through gas-phase etching by reactive gas such as ammonia.