Tiled GaN Seed Crystals for Low-Defect Substrate Growth
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Solution Overview
Problem
Current techniques for growing large-area gallium nitride substrates face challenges such as high defect levels, including threading dislocations, grain boundaries, and strain, which compromise the quality and reliability of optoelectronic and electronic devices, and lack cost-effective and efficient methods for reducing these defects.
Innovation Solution
A method for forming free-standing group III metal nitride crystals with a wurtzite crystal structure, involving a bulk crystal growth process on a tiled array of seed crystals with precise crystallographic orientation and thermal expansion matching, to achieve low defect densities and improved crystallographic registry, resulting in substrates with reduced threading dislocations and stacking faults.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If GaN deposition is performed on non-GaN substrates such as sapphire or GaAs, then large-area substrates can be manufactured, but threading dislocations arise at high concentrations (10^5-10^7 cm^-2)
Solution Approach 1:
The substrate is divided into multiple elementary seed crystals that are tiled together to form a composite substrate. Each seed crystal is grown separately with controlled defect density, and when tiled and overgrown, the defects are distributed rather than concentrated, achieving large area with reduced overall defect concentration.
Solution Approach 2:
The invention changes the substrate parameter from a single continuous non-GaN substrate to an array of discrete seed crystals with specific crystallographic orientations. By controlling the orientation and spacing parameters of the tiled seeds, the defect propagation is managed while maintaining large effective substrate area.
2Productivity
If conventional growth methods are used for gallium nitride crystals, then substrates can be produced, but defect levels remain high compromising device quality
Solution Approach 1:
Elementary seed crystals are prepared in advance with controlled crystallographic properties and defect characteristics before being tiled together. This preliminary preparation allows optimization of each seed's quality, and when assembled into a composite substrate, the overall defect concentration is reduced compared to growing a single large substrate directly.
3Area of stationary object
If vapor-phase methods such as HVPE are used for large area substrate manufacturing, then substrates can be produced, but the process is relatively expensive
Solution Approach 1:
The manufacturing process is segmented into growing multiple smaller elementary seed crystals that can be produced more economically, then tiling them together to achieve large effective area. This avoids the need for expensive single-crystal growth equipment and processes required for manufacturing large-area substrates in one piece.
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 method produces substrates with significantly lower defect densities, improved crystal quality, and reduced strain, enabling the production of large-area, high-quality gallium nitride substrates with enhanced device performance and reliability.
Implementation Method 1
performing a bulk crystal growth process on a tiled array of at least two seed crystals in a crystal growth apparatus
Implementation Method 2
The mechanical fixture comprises at least a backing plate member and a clamp member, each of which has a coefficient of thermal expansion that lies between 80% and 99% of the coefficient of thermal expansion of the at least two seed crystals
Data Source
AI summary
Embodiments of the present disclosure include techniques related to techniques for processing materials for manufacture of group-III metal nitride and gallium based substrates. More specifically, embodiments of the disclosure include techniques for growing large area substrates using a combination of processing techniques. Merely by way of example, the disclosure can be applied to growing crystals of GaN, AlN, InN, InGaN, AlGaN, and AlInGaN, and others for manufacture of bulk or patterned substrates. Such bulk or patterned substrates can be used for a variety of applications including optoelectronic and electronic devices, lasers, light emitting diodes, solar cells, photo electrochemical water splitting and hydrogen generation, photodetectors, integrated circuits, and transistors, and others.