Non-polar AlN Buffer Layer on Sapphire for DUVLEDs
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Solution Overview
Problem
The growth of high-quality non-polar AlN buffer layers on r-sapphire crystal plates is challenging due to surface roughening at high temperatures and difficulties in controlling the Al composition ratio in AlGaN layers, which affects the emission efficiency and wavelength stability of deep ultraviolet light-emitting diodes (DUVLEDs).
Innovation Solution
A manufacturing process involving a two-step or three-step growth of AlN buffer layers with a surface protection layer and a smoothing layer, optimized to suppress surface roughness and achieve a controlled Al composition ratio, is employed to create a high-quality non-polar AlN buffer layer on r-sapphire substrates, enabling improved crystallinity and flatness for subsequent AlGaN growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If high temperature treatment is used to manufacture a flat surface of the a-AlN layer, then surface flatness is improved, but the sapphire crystal plate surface becomes roughened due to oxygen loss
Solution Approach 1:
A surface protection layer is formed on the sapphire crystal plate before the main AlN buffer layer growth. This protection layer prevents oxygen loss and surface roughening during high-temperature treatment, enabling subsequent high-temperature growth to achieve flat surfaces without damaging the substrate
Solution Approach 2:
The surface protection layer acts as an intermediary between the sapphire crystal plate and the high-temperature growth environment. It mediates the thermal process by protecting the sapphire from direct exposure to conditions that cause oxygen loss, while still allowing the AlN buffer layer to grow with improved flatness
2Ease of manufacture
If conventional growth methods are used for AlN buffer layers, then manufacturing process is simple, but the Al composition ratio in AlGaN layers cannot be controlled, affecting emission efficiency and wavelength stability
Solution Approach 1:
The invention changes growth parameters including temperature, pressure, and gas flow rates during the AlN buffer layer formation process. These parameter modifications enable precise control of the Al composition ratio in subsequent AlGaN layers, achieving the desired emission efficiency and wavelength stability while maintaining a manageable manufacturing process
3Reliability
If non-polar plane is used for AlN buffer layer, then emission efficiency is improved, but manufacturing difficulty increases significantly
Solution Approach 1:
The AlN buffer layer formation is divided into multiple stages: initial layer formation, surface protection layer formation, and smoothing layer formation. This segmentation allows each stage to be optimized independently, making the complex non-polar plane manufacturing process more manageable while achieving the required emission efficiency
Solution Approach 2:
Surface protection and smoothing layers are formed preliminarily before the main AlGaN device structure is built. These preliminary actions prepare the non-polar surface with the required quality for high emission efficiency, while isolating the manufacturing complexity to separate preparatory steps
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 high-performance UV emission device with improved emission efficiency and wavelength stability, achieving a smooth surface with reduced defects and controlled Al composition, enhancing the performance of DUVLEDs.
Implementation Method 1
The AlN buffer layer comprises a surface protection layer and a smoothing layer, which are epitaxially grown layers made of AlN crystal
Implementation Method 2
The AlN buffer layer comprises a surface protection layer and a smoothing layer, which are epitaxially grown layers made of AlN crystal
Data Source
AI summary
To fabricate a practically useful non-polar AlN buffer layer on a sapphire crystal plate and manufacture a UV light-emitting device on a non-polar crystal substrate by adopting the crystal substrate as an example, an embodiment of the present invention provides a crystal substrate 1D comprising an r-plane sapphire crystal plate 10 and an AlN buffer layer 20D of non-polar orientation. The AlN buffer layer comprises a surface protection layer 22 and a smoothing layer 26. The surface protection layer suppresses roughness increase on a surface of the AlN buffer layer, and the smoothing layer makes the surface of the AlN buffer layer a smoothed surface. Also provided is a crystal substrate 11 comprising an AlN buffer layer 20T to which a dislocation blocking layer 24 for reducing crystallographic defects is added between the surface protection layer 22 and the smoothing layer 26. In another embodiment a deep UV light-emitting device is provided.