GaN Seed Crystal with Graded Buffer for Crack-Free Ammonothermal Growth
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Solution Overview
Problem
The challenge lies in growing high-quality gallium nitride (GaN) substrates with low dislocation density, as current methods like hydride vapor phase epitaxy face difficulties in reducing dislocation density below 10^5 cm^-2, and existing seed crystals often crack, especially on nitrogen-polar faces, hindering the production of high-end optoelectronic and electronic devices.
Innovation Solution
A group III nitride crystal with a nitrogen-polar c-plane face of high structural quality and a gradually degrading polycrystalline or amorphous second face is used as a seed for ammonothermal bulk growth, fabricated through epitaxial growth methods like HVPE, where growth conditions are adjusted to prevent cracking and allow self-separation into suitable wafers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional epitaxial growth methods are used to grow GaN substrates, then high structural quality can be achieved on the nitrogen-polar face, but the substrates develop cracks due to stress accumulation
Solution Approach 1:
The invention changes the growth parameters during the epitaxial process, specifically transitioning from conditions that produce high-quality crystalline structure to conditions that produce lower-quality polycrystalline or amorphous structure. This gradual parameter change creates a stress-gradient that prevents crack formation while maintaining the high-quality nitrogen-polar face needed for device fabrication.
Solution Approach 2:
The invention creates a substrate with non-uniform local quality: the nitrogen-polar face maintains high structural quality suitable for device growth, while the opposite face and intermediate regions have progressively degraded quality. This local quality gradient serves to distribute and relieve stress without compromising the functional surface.
2Ease of manufacture
If hydride vapor phase epitaxy is used to grow GaN, then epitaxial layers can be formed on heteroepitaxial substrates, but dislocation density remains high (above 10^5 cm^-2)
Solution Approach 1:
The invention performs a preliminary action by creating a graded buffer layer structure before growing the final high-quality epitaxial layer. This buffer layer with gradually degrading crystal structure absorbs dislocations and prevents them from propagating to the functional device layers, enabling low-dislocation-density GaN growth on cost-effective heteroepitaxial substrates.
3Manufacturing precision
If seed crystals with high structural quality are used for ammonothermal bulk growth, then high-quality bulk GaN can be produced, but the seed crystals crack during growth processes
Solution Approach 1:
The invention applies beforehand cushioning by creating a graded buffer layer with progressively degraded crystal quality that acts as a stress-absorbing cushion. This buffer layer is formed before the high-quality epitaxial growth, and it prevents stress-induced cracking during subsequent ammonothermal bulk growth processes while still allowing high-quality bulk crystal production.
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 crack-free, high-quality GaN substrates suitable for ammonothermal bulk growth, reducing stress and dislocation density, enabling the production of high-quality GaN wafers for advanced devices.
Implementation Method 1
growing a single crystalline or a highly oriented polycrystalline group III nitride layer on a substrate
Implementation Method 2
fabricated through epitaxial growth methods like HVPE
Data Source
AI summary
In one instance, the invention provides a group III nitride crystal having a first side exposing nitrogen polar c-plane of single crystalline or highly oriented polycrystalline group III nitride and a second side exposing group III polar surface, polycrystalline phase, or amorphous phase of group III nitride. Such structure is useful as a seed crystal for ammonothermal growth of bulk group III nitride crystals. The invention also discloses the method of fabricating such crystal. The invention also discloses the method of fabricating a bulk crystal of group III nitride by ammonothermal method using such crystal.