GaN Thin Film on Si-Diffused Sapphire Substrate
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Solution Overview
Problem
High defect density in gallium nitride (GaN) thin films grown on foreign substrates like sapphire due to lattice mismatches, which hinders their application in optoelectronic and high-power devices.
Innovation Solution
A thin film structure with a compliant intermediate layer, such as a Si-diffused or Si-ion-implanted sapphire layer, is used to reduce defect density by accommodating dislocations, where the bulk and shear moduli of the intermediate layer are lower than those of the substrate and epilayer, effectively mitigating lattice mismatch-induced defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If heteroepitaxy is used on foreign substrates like sapphire, then GaN thin films can be grown, but high defect density is generated due to lattice mismatches
Solution Approach 1:
A compliant layer is introduced as an intermediary between the sapphire substrate and the GaN epilayer. This compliant layer has lower bulk and shear moduli than both the substrate and epilayer, allowing it to accommodate lattice mismatches and reduce threading dislocation density in the GaN thin film.
Solution Approach 2:
The elastic properties (bulk modulus and shear modulus) of the intermediate layer are specifically engineered to be lower than those of the substrate and epilayer. This parameter change creates a compliant layer that can elastically deform to accommodate lattice mismatches, thereby reducing defect propagation to the GaN layer.
2Manufacturing precision
If lateral epitaxy techniques are used to reduce threading dislocation density, then defect density can be reduced to 10^6 cm^-2 or lower, but this is still much higher than GaAs homoepitaxy
Solution Approach 1:
The compliant layer serves as a mediator that fundamentally changes the dislocation behavior at the substrate-epilayer interface. By having lower elastic moduli, it allows dislocations to remain confined to the compliant layer through elastic relaxation, achieving ultra-low threading dislocation density without complex lateral epitaxy processes.
Solution Approach 2:
The patent utilizes a phase transition approach where the compliant layer undergoes elastic deformation to accommodate lattice mismatches. This elastic phase allows the system to absorb strain energy without generating threading dislocations in the GaN epilayer, achieving low defect density with simpler processing.
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
Significantly reduces defect density in GaN thin films, enabling their use in high-quality device applications by controlling strain and accommodating misfits, thus improving the structural integrity and performance of GaN-based devices.
Implementation Method 1
the intermediate layer may be elastically softer than the epilayer to accommodate dislocations generated due to lattice mismatches between the first material and the third material
Implementation Method 2
an upper part of the supporting substrate facing the epilayer includes a layer of the sapphire into which silicon (Si) is diffused or ion-implanted through a top surface of the supporting substrate
Implementation Method 3
an upper part of the supporting substrate facing the epilayer includes a layer of the sapphire into which silicon (Si) is diffused or ion-implanted through a top surface of the supporting substrate
Data Source
AI summary
Provided are a thin film structure capable of remarkably reducing the defect density of gallium nitride (GaN), and a method of fabricating the same. The thin film structure includes a supporting substrate including sapphire, and an epilayer disposed on the supporting substrate and including gallium nitride (GaN). An upper part of the supporting substrate facing the epilayer includes a layer of sapphire into which silicon (Si) is diffused or ion-implanted through a top surface of the supporting substrate.