TiN Buffer Layer for GaN on Silicon Crack Prevention
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Solution Overview
Problem
The use of silicon substrates in GaN-based light emitting devices is hindered by thermal expansion issues causing cracks between the silicon substrate and the GaN thin film layer, and existing buffer layers like AlN do not fully utilize the higher electrical conductivity of silicon substrates due to their lower conductivity.
Innovation Solution
A method of growing GaN single crystals on a silicon substrate using a TiN group metal nitride buffer layer, accompanied by a nano-pattern of silicon oxide, which reduces lattice mismatch and thermal expansion-related cracks, and allows for the formation of electrodes on the substrate's lower surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a silicon substrate is used to reduce manufacturing costs, then manufacturing cost is reduced, but thermal expansion causes severe cracks between the silicon substrate and the GaN thin film layer
Solution Approach 1:
A buffer layer comprising a TiN group metal nitride is introduced as an intermediary between the silicon substrate and the GaN thin film layer. This buffer layer has a thermal expansion coefficient that is intermediate between silicon and GaN, thereby reducing the thermal expansion mismatch and preventing crack formation while allowing the use of cost-effective silicon substrates.
Solution Approach 2:
The invention changes the material parameter (thermal expansion coefficient) by selecting a TiN group metal nitride for the buffer layer, which has suitable thermal and electrical conductivity properties. This parameter selection resolves the contradiction by matching the buffer layer's thermal expansion characteristics to reduce stress while maintaining electrical conductivity for substrate bias application.
2Reliability
If an AlN buffer layer is used to prevent cracks, then crack formation is reduced, but the higher electrical conductivity of the silicon substrate cannot be utilized due to the lower conductivity of the AlN layer
Solution Approach 1:
The invention changes the material selection from AlN to TiN group metal nitrides, which have higher electrical conductivity while maintaining suitable thermal expansion properties. This parameter change allows both crack prevention and utilization of the silicon substrate's high electrical conductivity for applying substrate bias to improve carrier concentration and device performance.
Solution Approach 2:
The invention uses a composite structure where the TiN group metal nitride buffer layer combines the beneficial properties of both AlN (crack prevention through thermal expansion matching) and highly conductive materials (electrical conductivity for substrate bias). This composite approach resolves the contradiction by integrating multiple functions in a single buffer layer material.
3Ease of manufacture
If a sapphire substrate is used, then the GaN thin film layer can be formed, but the substrate is non-conductive making it impossible to form an electrode on the lower surface
Solution Approach 1:
The TiN group metal nitride buffer layer serves as a conductive intermediary between the silicon substrate and the GaN thin film layer. This allows the silicon substrate's high electrical conductivity to be utilized for forming an electrode on the lower surface, simplifying the device structure and enabling substrate bias application while still supporting GaN film formation.
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 growth of high-quality GaN single crystals with improved crystallinity and electrical conductivity, reducing manufacturing costs and increasing productivity by utilizing a larger silicon substrate and enabling a vertical electrode structure for enhanced light emission efficiency.
Implementation Method 1
thermal expansion may cause severe cracks to form between the silicon substrate and the GaN thin film layer
Implementation Method 2
reduces lattice mismatch and thermal expansion-related cracks
Implementation Method 3
due to the higher electrical conductivity of the silicon substrate or other like substrate, an electrode may be formed on a lower surface of the silicon substrate
Implementation Method 4
due to the higher electrical conductivity and higher thermal conductivity of the silicon substrate
Data Source
AI summary
Example embodiments are directed to a method of growing GaN single crystals on a silicon substrate, a method of manufacturing a GaN-based light emitting device using the silicon substrate, and a GaN-based light emitting device. The method of growing the GaN single crystals may include forming a buffer layer including a TiN group material or other like material on a silicon substrate, forming a nano-pattern including silicon oxide on the buffer layer, and growing GaN single crystals on the buffer layer and the nano-pattern.