GaN Semiconductor Structures with Lattice-Matched Nucleation Layers
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The growth of gallium nitride (GaN) thin films on sapphire substrates results in three-dimensional growth mode due to lattice mismatch and thermal expansion differences, leading to structural defects that degrade the quality of the film, necessitating a buffer layer to achieve high-quality epitaxial growth.
Innovation Solution
A semiconductor structure comprising a polycrystal substrate with a first single crystal layer that serves as a nucleation layer, matched in lattice and thermal expansion to the substrate, reducing dislocation density and residual stress, allowing for the growth of a thick, high-purity second single crystal layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If GaN is directly grown on a sapphire substrate, then the growth process is simplified, but the layer contains structural defects such as point defects, misfit dislocations, and stacking faults
Solution Approach 1:
The patent introduces a buffer layer composed of low-temperature grown AlN or GaN as an intermediary between the sapphire substrate and the subsequent high-quality GaN layer. This buffer layer provides nucleation sites for two-dimensional GaN growth at higher temperatures, effectively mediating the interface between the dissimilar sapphire substrate and GaN film, thereby reducing misfit dislocations and improving overall film quality without significantly complicating the growth process
2Manufacturing precision
If a buffer layer is introduced to improve GaN layer properties, then the film quality is improved, but the device complexity increases
Solution Approach 1:
The patent employs parameter changes by controlling the buffer layer thickness and growth temperature to optimize GaN layer properties. By systematically varying these parameters, high-quality GaN films are achieved with reduced defect densities. The buffer layer thickness is carefully controlled, and growth temperature is adjusted to transition from three-dimensional to two-dimensional growth mode, thereby improving film quality while maintaining reasonable structural complexity
3Adaptability or versatility
If GaN is grown on sapphire substrate, then the thermal expansion difference and lattice mismatch are present, but no suitable crystalline substrate with lattice parameter near GaN is available
Solution Approach 1:
The buffer layer serves as a mediator that accommodates the lattice mismatch and thermal expansion difference between sapphire and GaN. By providing a transition layer with intermediate properties, the buffer layer reduces the harmful effects of direct interface mismatch, enabling successful GaN growth on readily available sapphire substrates without requiring exotic materials
4Productivity
If three-dimensional growth mode occurs due to lattice mismatch, then the growth rate is higher, but the layer contains structural defects that degrade film properties
Solution Approach 1:
The patent employs periodic action by first growing a low-temperature buffer layer in three-dimensional mode to establish nucleation sites, then transitioning to high-temperature two-dimensional growth mode for the main GaN layer. This periodic switching between growth conditions allows the initial rapid three-dimensional growth to be followed by high-quality two-dimensional growth, thereby achieving both reasonable growth rate and excellent structural quality
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 approach results in reduced dislocation density and elimination of defects like stacking faults, enabling the growth of a thick, high-purity single crystal layer suitable for optoelectronic devices with improved structural and electronic properties.
Implementation Method 1
The first single crystal layer serves as a nucleation layer for growth of the second single crystal layer
Implementation Method 2
due to their similar coefficients of thermal expansion (CTE), residual stress between the polycrystal substrate and the nucleation layer is effectively reduced when cooling subsequent to a high temperature process
Data Source
AI summary
A semiconductor structure is disclosed. The semiconductor structure includes a polycrystal substrate, a first single crystal layer formed thereon and a second single crystal layer formed on the first single crystal layer. A variation of coefficients of thermal expansion (CTE) between the first single crystal layer and the polycrystal substrate is less than 25%. There is no lattice mismatch between the first single crystal layer and the polycrystal substrate.