Patterned Si Substrate LED Wafer with Al2O3 Coating
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Solution Overview
Problem
The challenge in preparing high-quality GaN epitaxial layers on Si substrates is due to melt-back reactions and surface defects, which hinder the growth of single crystal films and lead to stress-induced cracking, while conventional substrates like sapphire have limitations in thermal conductivity and cost.
Innovation Solution
A patterned Si substrate with an Al2O3 coating is used, allowing for the growth of a GaN or AlGaN nucleation layer and a stress buffer layer, enabling single crystal growth and reducing dislocation density, thereby improving light extraction efficiency and device stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If GaN epitaxial layer is grown directly on Si substrate, then manufacturing cost is reduced and thermal conductivity is improved, but surface cracking occurs due to large stress and melt-back reaction
Solution Approach 1:
The patent introduces an Al2O3 coating layer as an intermediary between the Si substrate and GaN epitaxial layer. This coating prevents the melt-back reaction between Si and Ga atoms while reducing thermal stress, thereby eliminating surface cracking without sacrificing the cost advantages of Si substrates
Solution Approach 2:
The Al2O3 coating is applied to the Si substrate before epitaxial growth of GaN. This preliminary action prevents the harmful melt-back reaction from occurring during the subsequent high-temperature GaN growth process, ensuring surface integrity from the outset
2Reliability
If AlN nucleation layer is grown on patterned Si substrate to avoid melt-back reaction, then surface defects are reduced, but single crystal growth is hindered due to columnar growth mode
Solution Approach 1:
The Al2O3 coating serves as a superior intermediary compared to AlN nucleation layer. It provides a stable platform that promotes epitaxial growth of GaN in the preferred (002) orientation, enabling single crystal growth while still preventing the melt-back reaction between Si and Ga
Solution Approach 2:
The patent changes the coating material from AlN to Al2O3, which fundamentally alters the growth characteristics. Al2O3 promotes single crystal GaN growth by suppressing columnar growth mode and enabling epitaxial orientation control, thereby resolving the single crystal growth issue
3Illumination intensity
If sapphire substrate is used for GaN growth, then light extraction efficiency is improved, but thermal conductivity is reduced making heat dissipation difficult
Solution Approach 1:
The patent applies the patterned substrate concept to Si, creating local optical field modulation through patterns on the Si substrate. This enables light extraction enhancement at specific locations while maintaining the overall high thermal conductivity advantage of the Si substrate
Solution Approach 2:
The patent creates a composite structure combining Si substrate with Al2O3 coating and patterned features. This composite approach retains the high thermal conductivity of Si while adding the light extraction enhancement capabilities through the coating and patterns
4Illumination intensity
If Si substrate is stripped and back surface roughening is performed to improve light extraction, then light extraction efficiency increases, but device complexity and process difficulty increase
Solution Approach 1:
The Al2O3 coating is applied in advance to the Si substrate before any other processing steps. This preliminary coating simplifies subsequent processes by eliminating the need for substrate stripping and complex back surface roughening operations, as the coating itself can be patterned to provide light extraction enhancement
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 enables the production of high-power, cost-effective GaN-based LED epitaxial wafers with enhanced light extraction and reduced surface cracking, improving the operational stability and efficiency of LED devices.
Implementation Method 1
the Si substrate may react with Ga atoms in the atmosphere of ammonia (NH3) (referred to as a 'melt-back reaction'), causing a large amount of surface defects
Implementation Method 2
A patterned Si substrate with an Al2O3 coating is used, allowing for the growth of a GaN or AlGaN nucleation layer and a stress buffer layer
Implementation Method 3
the other is to prepare the LED epitaxial wafer on the patterned Sapphire Substrate (PSS), so that to increase the light reflected from the bottom by using the bottom of the patterned substrate
Implementation Method 4
the main problem with epitaxially growing GaN on a Si substrate is the presence of large stress in the GaN-on-Si epitaxial film, which causes surface cracking problems
Data Source
AI summary
An patterned Si substrate-based LED epitaxial wafer and a preparation method therefor, the LED epitaxial wafer comprising: a patterned Si substrate (1) and an Al2O3 coating (2) growing on the patterned Si substrate (1); sequentially growing on the Al2O3 coating (2) are a nucleating layer (3), a first buffer layer (4), a first insertion layer (5), a second buffer layer (6), a second insertion layer (7), an n-GaN layer (8), a quantum well layer (9), a p-GaN layer (10), an n-electrode (14) electrically connected to the n-GaN layer and a p-electrode (13) electrically connected to the p-GaN layer. The present invention is suitable for the preparation of large-sized LED epitaxial wafers. Furthermore, the crystal quality is improved, and the light extraction efficiency of the LED die is improved.