GaN Nanostructure Template for Low-Defect Substrate Growth
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Solution Overview
Problem
The production of high-quality, thick, and commercially viable free-standing GaN substrates is hindered by lattice mismatch and thermal expansion coefficient differences between deposited films and substrates, leading to high dislocation densities and substrate bending/cracking in nitride-based optoelectronic and microelectronic devices.
Innovation Solution
A method involving the growth of semiconductor nanostructures using a template with a dielectric and metal mask, followed by epitaxial lateral overgrowth and vertical growth using HVPE, which reduces defect density and strain by decoupling the substrate's impact through nano-column compliant layers, allowing for the production of thick, flat, and low-defect GaN films.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If alternative substrates (sapphire, SiC) are used for GaN growth, then device fabrication becomes feasible, but high dislocation density and wafer bending/cracking occur due to lattice mismatch and thermal expansion differences
Solution Approach 1:
The invention segments the GaN layer into numerous nanocolumns (10-100 nm diameter) grown on the substrate, rather than forming a continuous thin film. This segmentation allows each nanocolumn to accommodate lattice mismatch and thermal stress independently, preventing wafer bending and cracking while maintaining overall structural integrity for device fabrication
Solution Approach 2:
The invention changes the morphological parameters of the GaN layer from a continuous two-dimensional film to a three-dimensional array of nanocolumns with controlled diameter (10-100 nm), spacing, and height. This parameter change enables the structure to tolerate lattice mismatch and thermal expansion differences, reducing dislocation density to 10^6-10^7 cm^-2 while preserving substrate compatibility
2Reliability
If conventional epitaxial lateral overgrowth (ELOG) is used, then dislocation density is reduced to 10^7 cm^-2, but only one fifth of the wafer surface area achieves low defect density
Solution Approach 1:
The invention uses a self-organized nanocolumnar growth mode where numerous nanocolumns (occupying the entire wafer surface) are formed simultaneously, rather than relying on lateral overgrowth from limited oxide stripe regions. This segmentation approach distributes low-defect regions across the entire wafer area, not just localized zones
Solution Approach 2:
The nanocolumns serve a dual function: they act as both the growth template and the final low-defect semiconductor structure. The nanocolumns self-organize during growth to accommodate dislocations at their bases, allowing the upper portions to achieve ultra-low defect densities across the entire wafer surface
3Reliability
If bulk GaN growth techniques are used, then low dislocation density is achieved, but very high pressure (~15 kbar) is required
Solution Approach 1:
The invention introduces an intermediary nanocolumnar structure that mediates between the substrate and the overgrown GaN layer. These nanocolumns, grown at moderate pressures, serve as defect-filtering templates that enable subsequent low-pressure growth of high-quality GaN, avoiding the need for extreme bulk growth pressures
Solution Approach 2:
The invention changes the growth parameters from bulk high-pressure conditions to a two-stage process: first growing nanocolumns at moderate pressure, then overgrowing at lower pressure. This parameter change achieves comparable or superior defect reduction without requiring the extreme ~15 kbar pressure needed for bulk growth
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 enables the mass production of high-quality, thick, and strain-free GaN substrates with reduced defect density and minimal substrate tilting, facilitating the growth of continuous, crack-free GaN films that can be readily separated and used as seeds for further growth, thus overcoming the limitations of existing techniques.
Implementation Method 1
The semiconductor layer may formed by deposition onto the substrate by epitaxial growth methods
Implementation Method 2
in step (c), the nanostructures are formed by etching the template material, which may be by wet, dry or combined wet and dry etching
Implementation Method 3
Epitaxial lateral overgrowth technique (so-called ELOG and its modifications: facet initiated epitaxial lateral overgrowth (FIELO) and Pendeo
Implementation Method 4
nanopendeo growth bends all defects strongly at the interface of ELOG GaN and nanocolumns
Implementation Method 5
The small dimension of the nanocolumns will also minimize the facet tilt in the grain boundary of lateral overgrown layer. The controlled dimension of the nanocolumns and the localized stress between the nanocolumn and lateral-grown layer also allows the thick semiconductor
Data Source
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AI summary
A method of producing single-crystal semiconductor material comprises: providing a template material; creating a mask on top of the template material; using the mask to form a plurality of nanostructures in the template material; and growing the single-crystal semiconductor material onto the nanostructures.