GaN Buffer Layer with Oxygen Gradient for Crystal Quality
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Solution Overview
Problem
The lattice mismatch between gallium nitride (GaN) material and the substrate in LED chip manufacturing reduces crystal quality and luminescent efficiency due to material stress and dislocation density, exacerbated by the introduction of oxygen during reactive sputtering which affects the density and thickness of aluminum nitride (AlN) buffer layers.
Innovation Solution
A buffer layer comprising alternating semiconductor material layers and oxygen-doped material layers is deposited on a substrate, with oxygen concentrations decreasing from the substrate to the epitaxial layer, using a physical vapor deposition process that minimizes gaps between depositions and reduces stress through continuous growth, enhancing lattice matching and crystal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a single-layer AlN buffer layer is deposited using reactive sputtering, then the deposition process is simple and fast, but oxygen is introduced during the process which reduces the density and increases the thickness of the buffer layer, leading to poor crystal quality
Solution Approach 1:
The buffer layer is segmented into multiple alternating layers of AlN and Al-rich AlN with different oxygen concentrations. This segmentation allows control of oxygen content in each sub-layer while maintaining overall buffer functionality, resolving the contradiction between fast deposition and crystal quality by enabling separate optimization of each layer's properties
Solution Approach 2:
Different regions of the buffer layer are given different local qualities through varying oxygen concentrations in alternating layers. The Al-rich AlN layers have higher oxygen content to compensate for oxygen loss during MOCVD, while pure AlN layers provide dense crystal structure, achieving both fast deposition and high crystal quality through spatially varying properties
2Ease of manufacture
If oxygen is introduced during reactive sputtering to form AlN buffer layer, then the buffer layer can be formed, but the oxygen reduces the density of the buffer layer and causes thickness variation, negatively affecting the luminescent efficiency
Solution Approach 1:
The harmful effect of oxygen introduction during reactive sputtering is converted into a benefit by deliberately introducing oxygen in controlled amounts in alternating layers. The Al-rich AlN layers are designed to have higher oxygen content to compensate for oxygen loss during subsequent MOCVD processing, transforming the harmful oxygen introduction into a beneficial pre-doping strategy that improves crystal quality and luminescent efficiency
Solution Approach 2:
The oxygen concentration parameter is changed spatially by creating alternating layers with different oxygen contents. This parameter change allows the buffer layer to have regions optimized for different functions: some regions compensate for oxygen loss during MOCVD while others maintain high density, thereby improving overall reliability and luminescent efficiency
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 solution effectively reduces material stress and dislocation density, improving the crystal quality and luminescent efficiency of epitaxial GaN material grown on the buffer layer, leading to higher-quality LED chips with improved reliability.
Implementation Method 1
using a physical vapor deposition process that minimizes gaps between depositions
Data Source
AI summary
A semiconductor wafer includes a substrate (1), a buffer layer (2) deposited on the substrate (1), and an epitaxial layer (4) above the buffer layer (2). The buffer layer (2) includes a plurality of semiconductor material layers (22) and a plurality of oxygen-doped material layers (21). The semiconductor material layers (22) and the oxygen-doped material layers (21) are deposited in an alternating arrangement on top of each other. Oxygen concentrations of the oxygen-doped material layers (21) gradually decrease along a direction from the substrate (1) to the epitaxial layer (4).