Porous Graphene Buffer Layer for GaN on Sapphire Mismatch
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Solution Overview
Problem
The existing semiconductor technologies face challenges in reducing lattice and thermal mismatches between gallium nitride (GaN) epilayers and sapphire substrates, which affect the crystallinity, electrical, and optical properties of GaN epilayers, and are hindered by the limitations of conventional buffer layer materials.
Innovation Solution
A semiconductor structure utilizing a multi-layer porous graphene film as a buffer layer between the gallium nitride and sapphire substrate, fabricated through metalorganic chemical vapor deposition, etching, and photolithography processes, to address lattice and thermal mismatches, with the graphene film enhancing heat dissipation and reducing defect density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional buffer layer is formed on the sapphire substrate to reduce lattice and thermal mismatch, then the crystallinity and electrical property of gallium nitride epilayer are improved, but the material selection is restricted and the fabrication complexity increases
Solution Approach 1:
The invention changes the material parameter from conventional buffer layer materials to graphene, which has unique physical properties including high thermal conductivity and lattice structure that can accommodate the mismatch between sapphire substrate and gallium nitride epilayer. This parameter change resolves the contradiction by providing a material that improves crystallinity without restricting material selection
Solution Approach 2:
Graphene serves as an intermediary layer between the sapphire substrate and gallium nitride epilayer, mediating the lattice and thermal expansion coefficient mismatch. The graphene layer acts as a buffer that absorbs the mechanical and thermal stress, thereby improving the overall reliability of the semiconductor structure while simplifying the fabrication process
2Reliability
If a thicker graphene and graphene oxide layer is used as the intermediate layer, then the lattice mismatch is reduced, but the thickness cannot be reduced below 2.2 nm even after annealing process
Solution Approach 1:
The invention uses porous graphene with controlled pore sizes and distributions. The porous structure allows the graphene layer to maintain its lattice mismatch reduction functionality while achieving a thickness below 2.2 nm. The pores provide space for stress relaxation and accommodate the lattice difference between substrate and epilayer
Solution Approach 2:
The graphene layer is designed with local variations in pore size, density, and distribution to optimize both thickness reduction and lattice mismatch compensation. Different regions of the graphene layer have different pore characteristics tailored to local stress and lattice requirements, enabling thin film functionality
3Reliability
If graphene is used as the buffer layer material, then the resistance value is reduced and thermal conductivity is improved, but the fabrication process requires additional steps such as annealing and thickness control
Solution Approach 1:
The porous structure is created in the graphene layer before the gallium nitride epilayer growth. This preliminary pore formation allows the subsequent epilayer growth to proceed without requiring additional annealing steps for thickness reduction, as the porous structure already provides the necessary stress relief and lattice accommodation
Solution Approach 2:
The porous graphene layer performs multiple functions simultaneously: it acts as a buffer for lattice mismatch, provides thermal management through high thermal conductivity, offers electrical contact with low resistance, and enables controlled epilayer growth. This multi-functionality reduces the need for separate processing steps
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 multi-layer porous graphene film effectively reduces lattice and thermal mismatches, improving the quality of gallium nitride epilayers, increasing light emitting efficiency of LEDs, and facilitating heat dissipation, while being transparent to maintain light emission in LED applications.
Implementation Method 1
the porous graphene film effectively reduces lattice and thermal mismatches
Implementation Method 2
the porous graphene film effectively reduces lattice and thermal mismatches... facilitating heat dissipation
Implementation Method 3
the thickness of porous graphene is controlled to be less than 2.2 nm... the porous graphene film enhancing heat dissipation
Data Source
AI summary
A semiconductor structure having a multiple-porous graphene layer includes a sapphire substrate, a single or multiple layer porous graphene film, and a gallium nitride layer. A fabrication method for forming the semiconductor structure having a single or multiple layer porous graphene film, includes: firstly, growing up the graphene on the copper foil; then, using the acetone and isopropyl alcohol to wash the sapphire substrate, and then using the nitrogen flow to dry up; transferring the graphene onto the semiconductor substrate, using the Poly(methyl methacrylate) to fix the single or multiple layer porous graphene film, and using the acetone to wash up; using the photolithography process to etch the whole surface of the multiple-porous graphene layer; and, using the metalorganic chemical vapor deposition to deposit gallium nitride on the single or multiple layer porous graphene film and the sapphire substrate.