Composite Substrate for GaN Growth via Laser Lift-Off
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Solution Overview
Problem
Current GaN-based semiconductor devices face challenges due to lattice mismatch and thermal stress when grown on sapphire or SiC substrates, leading to poor crystal quality, reduced efficiency, and high costs, making it difficult to produce high-power LEDs with vertical structures and good heat dissipation.
Innovation Solution
A composite substrate with a thermally and electrically conductive layer bonded to a GaN mono-crystalline layer, allowing for iso-epitaxial growth and reducing production costs, enabling the formation of high-quality vertical structure LEDs with improved light emission efficiency and heat dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If GaN epitaxial films are grown on sapphire substrates, then the substrates are widely available and the growth process is well-established, but large lattice mismatch and thermal stress produce high concentration of dislocations
Solution Approach 1:
The patent uses SiC as an intermediary substrate layer between the sapphire carrier and the GaN epitaxial layer. The SiC layer acts as a mediator that reduces the lattice mismatch and thermal stress between sapphire and GaN, thereby decreasing dislocation concentration while maintaining the manufacturing advantages of sapphire substrates
Solution Approach 2:
The patent creates a composite substrate structure consisting of multiple layers: sapphire carrier substrate, SiC buffer layer, and GaN epitaxial layer. This composite structure combines the advantages of each material - the availability of sapphire, the lattice matching of SiC, and the desired GaN film properties
2Manufacturing precision
If SiC substrates are used for GaN growth, then lattice parameters are most close to GaN and lattice mismatch is smaller, but SiC is expensive making it unsuitable for many GaN-based optoelectronic devices
Solution Approach 1:
The patent segments the substrate function into two separate components: the sapphire carrier substrate provides mechanical support and thermal stability at low cost, while the SiC buffer layer provides the lattice-matched surface for GaN growth. This segmentation allows each material to perform its optimal function without requiring the entire substrate to be expensive SiC
3Manufacturing precision
If GaN mono-crystalline substrates are used, then iso-epitaxy is achieved and crystal quality is improved, but the high cost severely restricts usage in LED devices
Solution Approach 1:
The SiC buffer layer serves as an intermediary that enables the growth of high-quality GaN epitaxial films on inexpensive sapphire substrates. This intermediary layer provides the necessary crystallographic template and stress management to achieve near-iso-epitaxial quality without requiring expensive GaN mono-crystalline substrates
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 composite substrate enhances the crystalline quality of GaN epitaxial sheets, increases quantum efficiency, and allows for the direct preparation of vertical structure LEDs, overcoming the limitations of traditional substrates while reducing production costs.
Implementation Method 1
a thermally and electrically conductive layer (1) and a GaN mono-crystalline layer (2) on the thermally and electrically conductive layer
Implementation Method 2
iso-epitaxy is a optimal selection... GaN epitaxy return to iso-epitaxy, and improves the quality of epitaxially grown GaN crystal
Data Source
Figure 1~3
Figure 4~7
Figure 8(a)~8(d)
AI summary
The present application discloses method for preparing a composite substrate for GaN growth. The method comprises: first growing a GaN mono-crystalline epitaxial layer on a sapphire substrate, then bonding the GaN epitaxial layer onto a temporary substrate with an epoxy-type instant adhesive, lifting off the sapphire substrate by laser, then bonding the GaN epitaxial layer on the temporary substrate with a thermally and electrically conductive substrate, shedding the temporary substrate, and so obtaining the composite substrate in which the GaN layer of face-up gallium polarity is bonded to the thermally and electrically conductive substrate. When the GaN layer on the sapphire substrate is directly bonded to the thermally and electrically conductive substrate and the sapphire substrate is lifted off by laser, a composite substrate in which a GaN epitaxial sheet of face-up nitrogen polarity is bonded to the thermally and electrically conductive substrate is obtained. The composite substrate prepared in the present invention not only has homo-epitaxy and improves the quality of crystals but also can be used directly for the preparation of LEDs with a vertical structure, and merely uses a thin layer of GaN mono-crystalline , greatly reducing costs and possessing advantages in applications.