GaN Substrate Trench Segmentation for Dislocation Reduction
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Solution Overview
Problem
Current techniques for growing large-area gallium nitride substrates suffer from high defect levels, including threading dislocations, grain boundaries, and strain, which compromise the quality and reliability of optoelectronic and electronic devices, and are costly and inefficient.
Innovation Solution
The development of a free-standing group III metal nitride crystal with a wurtzite structure, featuring a maximum dimension greater than 40 millimeters, low average concentration of stacking faults, and varying threading dislocation density, achieved through a combination of processing techniques including lateral epitaxial overgrowth and ammonothermal growth, with a patterned mask layer and trench formation to reduce dislocation density and miscut variation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If GaN deposition is performed on a non-GaN substrate such as sapphire or GaAs, then large-area substrates can be grown, but threading dislocation concentration increases to 10^5-10^7 cm^-2
Solution Approach 1:
The substrate surface is segmented into multiple independent growth regions separated by trenches. Each region grows as an isolated crystal domain, preventing dislocation propagation between regions. The trenches act as physical barriers that segment the continuous substrate surface into discrete growth zones, thereby reducing overall dislocation concentration in the final large-area substrate.
Solution Approach 2:
The harmful element (dislocations) is extracted or removed from the growth process by using trenches to isolate and contain dislocations within specific regions. The trenches effectively 'take out' the dislocation propagation pathway, preventing defects from spreading across the entire substrate area and allowing large-area growth with reduced dislocation concentrations.
2Reliability
If conventional growth methods are used to overcome defects, then device performance may be maintained, but fabrication processes become complex and tedious
Solution Approach 1:
The trenches are formed and the growth regions are defined before the actual crystal growth process begins. This preliminary structuring of the substrate with pre-defined growth zones and barriers eliminates the need for complex post-growth defect correction processes. By preparing the substrate architecture in advance, the method simplifies the overall fabrication process while ensuring high device performance from the outset.
3Area of stationary object
If large-area substrates are grown by vapor-phase methods such as HVPE, then substrate size can be increased, but manufacturing cost increases significantly
Solution Approach 1:
The trenches serve as an intermediary structure that enables cost-effective large-area substrate growth. By introducing this simple geometric feature into the substrate, the method allows the use of more economical growth techniques while still achieving large substrate areas with acceptable quality. The trenches mediate between the requirements for large area and low cost, making the manufacturing process more economically viable.
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 substrates with significantly reduced defect densities, improved crystal growth quality, and increased substrate size, enabling the production of high-performance optoelectronic and electronic devices with enhanced reliability and efficiency.
Implementation Method 1
Ammonothermal crystal growth has a number of advantages over HVPE as a means for manufacturing GaN boules
Implementation Method 2
a free-standing laterally-grown ammonothermal group III metal nitride crystal or wafer
Implementation Method 3
Lateral epitaxial overgrowth (LEO) is a method that has been widely applied to improvement in the crystallographic quality of films grown by vapor-phase methods
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.