Graded Cl Concentration in AlN Buffer Layers for HVPE Growth
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Solution Overview
Problem
The challenge in growing high-quality AlN layers using the Hydride Vapor Phase Epitaxy (HVPE) method arises from the reaction of AlCl and NH3 before reaching the substrate, leading to difficulties in forming AlN layers with sufficient quality, and adjusting crystal growth conditions such as source gas flow rates does not adequately address this issue.
Innovation Solution
The solution involves forming a nitride semiconductor template with a Cl-containing AlN layer, where the Cl concentration gradually decreases from the substrate side to the nitride semiconductor layer side, achieved by controlling the flow rate of HCl gas during the growth process, ensuring a high Cl concentration on the substrate side and a lower concentration on the nitride semiconductor layer side, thereby preventing pits and improving crystal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If AlCl and NH3 are used as source materials in HVPE method, then AlN layer can be formed, but the source materials react before reaching the substrate surface causing insufficient quality
Solution Approach 1:
The patent introduces HCl gas as an intermediary substance that reacts with Al to form AlCl3 in the gas phase, which then transports Al to the substrate. This intermediary mechanism prevents direct reaction between AlCl and NH3 before substrate deposition, solving the premature reaction problem while maintaining AlN layer formation quality.
Solution Approach 2:
The patent optimizes multiple parameters including HCl gas flow rate (10-1000 sccm), Al source flow rate (10-100 sccm), NH3 flow rate (10-100 sccm), and substrate temperature (900-1100°C) to control the reaction kinetics and transport mechanisms, ensuring source materials reach the substrate without premature reaction while forming high-quality AlN layers.
2Device complexity
If uniform Cl concentration is maintained in AlN buffer layer, then layer formation is simplified, but Cl diffusion to nitride semiconductor layer causes increased contact resistance
Solution Approach 1:
The patent implements a graded Cl concentration distribution in the AlN buffer layer, where the Cl concentration is higher near the substrate and gradually decreases toward the nitride semiconductor layer. This local variation in composition prevents Cl diffusion to the active layer while maintaining the buffer layer's structural function, thereby reducing contact resistance without complicating the overall device structure.
Solution Approach 2:
The patent pre-establishes a Cl concentration gradient in the AlN buffer layer before forming the nitride semiconductor layer. This preliminary structuring of the buffer layer creates a diffusion barrier that prevents Cl from migrating to subsequent layers, proactively solving the contact resistance issue before device operation begins.
3Object-generated harmful factors
If source gas flow rates are increased to prevent premature reaction, then reaction prevention may improve, but crystal growth quality deteriorates
Solution Approach 1:
The patent optimizes the flow rates of HCl (10-1000 sccm), Al source (10-100 sccm), and NH3 (10-100 sccm) within specific ranges to balance two competing requirements: preventing premature reaction between source materials and ensuring high-quality crystal growth. This parameter optimization allows sufficient residence time for controlled reaction on substrate while preventing gas-phase reactions.
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 a nitride semiconductor template with improved crystal quality, as evidenced by reduced full width at half maximum (FWHM) values in X-ray rocking curves, and enables the production of high-brightness light-emitting elements with enhanced reliability and reduced manufacturing costs.
Implementation Method 1
When an AlN layer is formed by the HYPE method, AlCl and NH3 are generally used as source materials
Implementation Method 2
the Cl-free AlN buffer layer formed by the MOCVD method prevents diffusion of Cl from the Cl-containing AlN buffer layer
Data Source
AI summary
A nitride semiconductor template includes a substrate, an AlN layer that is formed on the substrate and that includes Cl, and a nitride semiconductor layer formed on the AlN layer. In the AlN layer, a concentration of the Cl in a region on a side of the substrate is higher than that in a region on a side of the nitride semiconductor layer. Also, a light-emitting element includes the nitride semiconductor template, and a light-emitting layer formed on the nitride semiconductor template.