LED Buffer Layer Pixelation for Stress Relaxation
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Solution Overview
Problem
The formation of light-emitting diodes (LEDs) is hindered by lattice mismatch and thermal coefficient of expansion (TCE) mismatch between GaN and substrate materials, leading to stress, defects, and warping in the GaN buffer layer and multiple quantum wells, which affects the emission color and yield.
Innovation Solution
A method involving the pixelation of the buffer layer into discrete islands by forming trenches into the buffer layer and substrate, allowing for stress relaxation and minimizing defects, enabling the growth of high-quality multiple quantum wells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick layer of AlN/GaN buffer growth is grown on the substrate to reduce defects, then the buffer layer thickness increases, but residual stress remains in the buffer layer affecting MQW growth
Solution Approach 1:
The buffer layer is segmented into discrete islands separated by trenches, transforming the continuous stressed layer into isolated regions. This segmentation allows each island to relax independently, eliminating residual stress while maintaining the protective function against defects.
Solution Approach 2:
Trenches are formed to extract and remove the stressed portions of the buffer layer, creating discrete islands. This extraction process eliminates the continuous stress path while retaining the functional buffer regions needed for defect protection.
2Strength
If the buffer layer is made continuous to provide uniform support, then structural support is improved, but stress relaxation is prevented leading to defects
Solution Approach 1:
The continuous buffer layer is divided into discrete islands, which provides localized structural support while allowing stress relaxation. Each island maintains its structural integrity for supporting MQWs while the separation enables stress relief.
Solution Approach 2:
Different regions serve different functions: the discrete buffer islands provide local structural support and stress relaxation, while the trenches provide stress relief pathways. This local differentiation resolves the contradiction between continuous support and stress relaxation.
3Productivity
If temperature is increased to facilitate GaN growth, then growth rate improves, but lattice mismatch and TCE mismatch cause expanded bowing and cracking
Solution Approach 1:
The buffer layer is segmented into discrete islands that can thermally expand and contract independently. This segmentation prevents the propagation of thermal stress-induced bowing and cracking that would occur in a continuous layer during temperature cycling.
Solution Approach 2:
The structural configuration of the buffer layer is changed from continuous to discrete islands, fundamentally altering how the layer responds to thermal parameters. This parameter change allows the system to tolerate temperature variations without developing excessive stress.
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 defect-free, stress-free LED structures with tight spectral distribution and high yield, suitable for various display applications, including TVs, mobile devices, and virtual/augmented/mixed reality products.
Implementation Method 1
relaxing the buffer layer by pixelating the buffer layer into discrete islands
Implementation Method 2
the use of GaN on a substrate has both a lattice mismatch and thermal coefficient of expansion (TCE) mismatch with the substrate
Implementation Method 3
a temperature ramp up can expand the GaN buffer layer about 2× more than the underlying Si material
Data Source
AI summary
The present disclosure generally relates to semiconductor structures and, more particularly, to light emitting diode (LED) structures and methods of manufacture. The method includes: forming a buffer layer on a substrate, the buffer layer having at least a lattice mismatch with the substrate; and relaxing the buffer layer by pixelating the buffer layer into discrete islands, prior to formation of a quantum well.