Selective Area Epitaxy GaN Film Release via AlN Etching
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Solution Overview
Problem
Gallium nitride-based devices fabricated on foreign substrates suffer from high defect densities due to lattice and thermal expansion mismatches, leading to inferior performance and high manufacturing costs, with existing substrate removal techniques being complex and costly.
Innovation Solution
The use of selective area epitaxy (SAG) combined with dry and wet etching techniques to grow high-quality gallium-nitride thin films on inexpensive substrates, allowing for the redirection of threading dislocations away from the active zone and enabling the reuse of substrates, thereby reducing defect densities and manufacturing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If foreign substrates (sapphire, Si) are used for GaN device fabrication, then substrate cost is reduced, but defect density increases due to lattice and thermal expansion mismatch
Solution Approach 1:
The substrate is segmented into multiple regions with different functions: a sacrificial release layer (AlN) is introduced between the substrate and the GaN epitaxial layer. This release layer can be selectively removed to detach the GaN layer from the substrate, enabling the use of inexpensive substrates while maintaining high material quality. The segmentation allows separation of the substrate's mechanical support function from the epitaxial growth function.
Solution Approach 2:
An AlN buffer layer serves as an intermediary between the foreign substrate and the GaN epitaxial layer. This intermediate layer accommodates the lattice and thermal expansion mismatch, reducing defect propagation to the active GaN regions. The buffer layer acts as a mediator that absorbs the incompatibility between substrate and epilayer materials.
2Reliability
If high-quality GaN substrates are used, then device performance improves with lower defect densities, but substrate cost increases significantly
Solution Approach 1:
The sacrificial AlN release layer is designed as a disposable component that is removed after serving its purpose of enabling epitaxial growth. This allows the use of inexpensive, disposable foreign substrates instead of expensive reusable GaN substrates, significantly reducing substrate costs while maintaining device performance through controlled defect management.
Solution Approach 2:
The invention creates local quality differentiation within the film structure: the AlN buffer layer region tolerates high defect densities from foreign substrates, while the GaN epitaxial layer grown on top maintains low defect densities in the active regions. This local quality separation allows inexpensive substrates to be used without compromising device performance in the critical active zones.
3Reliability
If selective area epitaxy with patterned mask is used, then threading dislocations are redirected away from active zones, but fabrication process complexity increases
Solution Approach 1:
A patterned mask is applied to the AlN buffer layer before epitaxial growth to define the locations where GaN will grow. This preliminary patterning redirects threading dislocations away from future active zones by controlling the nucleation and growth positions. The mask pattern is designed in advance to achieve optimal dislocation management before the critical device layers are formed.
Solution Approach 2:
The invention addresses the two-dimensional defect distribution problem by introducing a temporal dimension through sequential growth stages. First, the AlN buffer is grown with patterned mask to redirect dislocations, then the GaN layer is grown to planarize the surface and create low-defect active regions. This dimensional approach in the growth process enables defect management without excessive fabrication 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 results in high-performance gallium-nitride-based devices with reduced structural defects, improved lifetimes, and lower production costs, while allowing for the use of inexpensive substrates and simplified fabrication processes.
Implementation Method 1
The second thin film layer is grown from the first thin film layer through a patterned mask, having openings, under selective area growth (SAG) conditions
Implementation Method 2
The trench may provide access to the patterned mask and the patterned mask may be eliminated with a wet etchant
Data Source
AI summary
A thin film device described herein includes a first thin film layer, a second film layer and a heterostructure within the second film layer. The first thin film layer is atop a substrate. The second thin film layer is grown from the first thin film layer through a patterned mask, having openings, under selective area growth (SAG) conditions. The second thin film layer is configured to be released from the first thin film layer by etching a trench. The etched trench may provide access to the patterned mask and the patterned mask may be eliminated with a wet etchant.