Nitride LED Fabrication Using AlGaN Buffer Layer
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Solution Overview
Problem
The conventional methods for fabricating light emitting diodes using chemical vapor deposition (CVD) result in large lattice mismatch and stress between AlN thin film layers deposited by Physical Vapor Deposition (PVD) and nitride layers, leading to poor quality and low luminous efficiency, as well as warpage and non-uniform electric properties due to thick buffer layers and limited doping concentrations.
Innovation Solution
A fabrication method involving the deposition of an AlxInyGa1-x-yN material layer by CVD between the PVD AlN thin film layer and the CVD nitride layer, which reduces stress and improves lattice quality, and using a patterned substrate with a larger depth to enhance light extraction efficiency and reduce warpage, while allowing high-concentration doping for improved voltage characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If AlN thin film layer is deposited by PVD method, then the film is flat with low roughness and good lattice quality, but large stress and lattice mismatch occur with subsequent CVD nitride layers
Solution Approach 1:
An AlGaN intermediate layer is introduced between the PVD-deposited AlN thin film layer and the CVD-grown nitride layers. This intermediate layer serves as a transition layer that gradually adjusts the lattice constant from AlN to GaN, reducing the lattice mismatch and stress between the PVD AlN layer and subsequent CVD nitride layers. The AlGaN layer has compositional gradient or isotype structure that mediates the interface between two deposition methods.
2Manufacturing precision
If thick buffer layer is laminated to achieve smooth epitaxial layer surface, then the surface quality improves for subsequent layer lamination, but greater stress and warpage occur in LED structure
Solution Approach 1:
The thickness parameter of the buffer layer is optimized and reduced to minimal necessary thickness. Instead of using thick buffer layers, the patent employs precise control of buffer layer thickness combined with the AlGaN intermediate layer to achieve sufficient surface smoothness. This parameter optimization reduces the total buffer layer thickness, thereby reducing stress accumulation and warpage in the final LED structure.
3Illumination intensity
If pattern depth on substrate surface is increased to improve light extraction efficiency, then photon extraction improves, but MOCVD method cannot produce quality epitaxial film layer
Solution Approach 1:
The deposition process is segmented into two distinct stages: first, PVD method is used to deposit AlN thin film layer directly on the patterned substrate surface with deep patterns; second, CVD method is used to grow high-quality nitride layers on top of the PVD AlN layer. This segmentation allows the patterned substrate to retain its deep pattern structure for light extraction while the CVD process operates on a flat PVD AlN surface, ensuring high epitaxial layer quality.
4Reliability
If doping concentration of active layer is increased to improve voltage characteristics, then voltage performance improves, but quality of underlayer limits the maximum achievable doping level
Solution Approach 1:
The AlGaN intermediate layer acts as a mediator that decouples the underlayer quality constraints from the active layer doping requirements. By providing a high-quality transition interface between PVD AlN and CVD nitride layers, the AlGaN intermediate layer enables high doping concentrations in the active layer without being limited by underlayer quality issues. This intermediate structure allows independent optimization of underlayer and active layer properties.
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 method enhances the overall quality and luminous efficiency of light emitting diodes by reducing stress and warpage, improving electric uniformity, and increasing doping levels without affecting leakage, thus improving the yield and performance of light emitting diodes.
Implementation Method 1
Physical vapor deposition (PVD) refers to a technology that under a vacuum condition, material source—the solid or liquid surface—is gasified into gaseous atoms or molecules, or part of them is ionized into ions, and then through the low-pressure gas (or plasma) process, a special-purpose film is deposited on the substrate surface
Implementation Method 2
the deposition of the crystal layer by the chemical vapor deposition method
Implementation Method 3
the roughened GaN/substrate interface diffuses the photons emitted from the active region, so that the originally full-emitted photons have the opportunity to exit from the device
Data Source
AI summary
A fabrication method of a nitride semiconductor LED includes, an AlxInyGa1-x-yN material layer is deposited by CVD between an AlN thin film layer by PVD and a gallium nitride series layer by CVD, to reduce the stress effect between the AlN thin film layer and the nitride layer, improve the overall quality of the LED and efficiency. An AlN thin film layer is deposited on a patterned substrate having a larger depth by PVD, and a thin nitrogen epitaxial layer is deposited on the AIN thin film layer by CVD, which reduces the stress by reducing the thickness of the epitaxial layer and improves warpage of the wafer and electric uniformity of the single wafer; the light extraction efficiency is improved by using the large depth patterned substrate; further, the doping of high-concentration impurity in the active layer effectively reduces voltage characteristics without affecting leakage, thereby improving the overall yield.