III-V Nitride Epitaxy on Silicon via AlN Buffer Transition Structure
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Solution Overview
Problem
The growth of high-quality nitride films on silicon substrates is hindered by large lattice and thermal mismatches between GaN and silicon, poor wetting of GaN on silicon, high density cracking, and challenges in integrating with Si-based electronic devices, leading to poor film quality and morphology.
Innovation Solution
A transition structure using multiple layers of monocrystalline materials grown by MOCVD, including AlN and AlGaN, is employed to compensate thermal strain and reduce lattice mismatch, with a pre-seeding Al technique to improve wetting and suppress amorphous silicon nitride formation, allowing for high-quality epitaxial growth of GaN and other III-V nitride layers on silicon wafers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If GaN is directly grown on silicon substrate, then the growth process is simple, but the large lattice mismatch (17%) results in high-density dislocations and poor film quality
Solution Approach 1:
A transition structure consisting of multiple buffer layers (AlN, AlGaN, GaN) is introduced as an intermediary between the silicon substrate and the final GaN layer. This multi-layer buffer structure gradually transitions the lattice mismatch, reducing dislocation density from 10^8-10^9 cm^-2 at the Si interface to below 10^6 cm^-2 in the final GaN layer, thereby achieving high film quality without excessive process complexity
2Device complexity
If GaN is directly grown on silicon substrate, then the fabrication process is simplified, but the large thermal mismatch (30%-50%) causes high-density cracking
Solution Approach 1:
The buffer structure is segmented into multiple discrete layers (AlN layer 102, AlGaN layer 104, GaN layer 108) with different thicknesses and compositions. Each layer is optimized to manage thermal stress differently, with the AlN layer providing compressive stress to counteract tensile stress from thermal mismatch, preventing cracking while maintaining a manageable fabrication process
3Quantity of substance
If ammonia is used during nitride growth, then nitrogen supply is adequate, but nitridation of the Si surface occurs forming amorphous silicon nitride
Solution Approach 1:
The silicon substrate surface is pre-treated with a hydrogen-terminated surface formation step before nitride layer growth. This preliminary action passivates the silicon surface, preventing unwanted nitridation when ammonia is introduced during subsequent MOCVD growth, thereby maintaining surface quality while ensuring adequate nitrogen supply
4Device complexity
If GaN is grown directly on silicon, then the process is straightforward, but poor wetting of GaN on silicon impedes nucleation and results in poor morphology
Solution Approach 1:
An AlN buffer layer is introduced as an intermediary between the silicon substrate and GaN growth. The AlN layer exhibits excellent wetting properties on the silicon substrate, providing a suitable nucleation surface that improves GaN film morphology and eliminates the poor wetting issue while maintaining process simplicity
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 high-quality epitaxial nitride layers with reduced dislocation density and crack-free films, enabling the fabrication of semiconductor structures with improved performance and integration with Si-based devices, overcoming the limitations of existing technologies.
Implementation Method 1
by first growing an transition structure as the buffer on a silicon substrate by using a metal organic chemical vapor deposition (MOCVD) technique
Implementation Method 2
the wafer is initially subjected to a flux of aluminium precursor without ammonia for a few seconds. After the surface of the silicon is covered with about 1-2-monolayers of aluminium
Implementation Method 3
High quality epitaxial III-V nitride layers of monocrystalline materials are grown on silicon substrates
Implementation Method 4
The transition structure compensates thermal strain and reduces the lattice mismatch between gallium nitride, GaN, and silicon
Implementation Method 5
The transition structure compensates thermal strain and reduces the lattice mismatch between gallium nitride, GaN, and silicon
Data Source
AI summary
A method and structure for fabricating III-V nitride layers on silicon substrates includes a substrate, a transition structure having AlGaN, AlN and GaN layers, and a superlattice structure having AlGaN and GaN layers. In the invention, the large lattice mismatch (17%) between GaN and silicon is solved by using AlN as the first buffer layer with a 5:4 coincidence between AlN(0001) and Si(111) lattice to reduce the lattice mismatch to 1.3%.