Nitride Semiconductor Buffer Structure for Silicon Substrates
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Solution Overview
Problem
The growth of nitride-based semiconductor thin films on silicon substrates faces challenges due to lattice constant and thermal expansion coefficient differences, leading to increased dislocation density and crack formation, which affects the performance of devices like LEDs and power devices.
Innovation Solution
A semiconductor buffer structure is proposed, comprising a nucleation layer of AlN and a buffer layer with specific layer configurations of AlInGaN, which applies compressive stress to offset lattice and thermal expansion differences, reducing dislocation density and crack formation by inserting layers with varying Ga composition ratios and thicknesses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a nitride thin film is grown on a silicon substrate, then heat conductivity is improved and large-size substrate growth is enabled, but dislocation density increases and cracks are generated due to lattice constant and thermal expansion coefficient differences
Solution Approach 1:
An AlN nucleation layer is introduced as an intermediary between the silicon substrate and the GaN thin film. This intermediate layer serves as a buffer that partially accommodates the lattice mismatch and thermal expansion differences, reducing dislocation density and preventing crack formation while allowing the beneficial heat conductivity of the silicon substrate to be utilized
Solution Approach 2:
The patent employs a composite buffer layer structure consisting of multiple materials (AlN and AlGaN) with different properties. The AlN layer provides strong lattice matching to reduce dislocations, while the AlGaN layer with graded composition helps manage thermal expansion differences, creating a composite structure that addresses multiple interface problems simultaneously
2Manufacturing precision
If a buffer layer is formed to reduce dislocation density, then crystallinity is improved, but device complexity increases due to multiple layer configurations
Solution Approach 1:
The buffer layer is segmented into distinct functional layers: an AlN nucleation layer for initial dislocation reduction, followed by AlGaN buffer layers with graded aluminum composition. Each segment performs a specific function in the progressive reduction of dislocation density, allowing complex performance improvement through modular layer design
Solution Approach 2:
Different regions of the buffer layer structure have locally optimized properties: the AlN layer at the interface provides strong lattice matching, while the AlGaN layers have progressively varying aluminum compositions tailored to specific depth positions. This local optimization of material properties at different locations achieves high overall crystallinity
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 buffer layer structure effectively reduces dislocation density and crack formation, improving the crystallinity and compressive stress of nitride semiconductor layers, enabling the growth of high-quality thin films for large-size semiconductor devices.
Implementation Method 1
A buffer layer offsets a lattice constant difference between a silicon substrate and a nitride semiconductor thin film
Implementation Method 2
A buffer layer offsets a thermal expansion coefficient difference between a silicon substrate and a nitride semiconductor thin film
Implementation Method 3
the GaN thin film has to be grown to have low dislocation for performance improvement and to receive compressive stress for crack prevention
Data Source
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Figure 3A~3B
Figure 4~5
AI summary
A semiconductor buffer structure includes a silicon substrate, a nucleation layer formed on the silicon substrate, and a buffer layer formed on the nucleation layer. The buffer layer includes a first layer formed of a nitride semiconductor material having a uniform composition rate, a second layer formed of the same material as the nucleation layer on the first layer, and a third layer formed of the same material with the same composition ratio as the first layer on the second layer.