GaN Growth on Sapphire via Boron Nitride Buffer Layer
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Solution Overview
Problem
Conventional methods for growing wurtzite-structure AlGaInBN nitride semiconductors on sapphire substrates are complex, costly, and inefficient, with issues such as amorphous crystal deposition, high temperature requirements, and difficulties in transferring films to flexible or inexpensive substrates, leading to compromised device performance and light extraction efficiency.
Innovation Solution
A method involving the growth of a hexagonal boron nitride (h-BN) thin film on a sapphire substrate, followed by a wurtzite-structure AlxGa1-xN thin film, allowing for the deposition of a single-crystal wurtzite structure GaN thin film, which can be easily mechanically separated and transferred to alternative substrates using a graphite-type boron nitride buffer layer with van der Waals bonds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a buffer layer is grown on a sapphire substrate using conventional methods (LT-AlN, LT-GaN, or AlON), then single-crystal wurtzite-structure nitride semiconductor can be grown, but the process becomes complex and costly with multiple temperature changes and equipment requirements
Solution Approach 1:
The patent introduces a graphite-type boron nitride (t-BN) buffer layer as an intermediary between the sapphire substrate and the wurtzite-structure AlGaInBN layer. This t-BN layer serves as a mediator that accommodates the lattice mismatch and thermal expansion differences, enabling high-quality single-crystal growth without requiring complex multi-step buffer layer processes like LT-AlN or AlON. The t-BN layer is grown at a moderate temperature of 1000-1100°C, simplifying the overall process while maintaining crystal quality.
2Reliability
If wurtzite-structure AlGaInBN is grown on a sapphire substrate, then devices can be manufactured, but the large lattice mismatch and thermal expansion coefficient difference make it difficult to grow single-crystal structures
Solution Approach 1:
The graphite-type boron nitride (t-BN) buffer layer acts as a mediator that resolves the lattice mismatch and thermal expansion coefficient difference between the sapphire substrate and the wurtzite-structure AlGaInBN. The t-BN layer has a hexagonal structure that provides a suitable template for wurtzite-phase nucleation, enabling high-quality single-crystal growth despite the significant differences between sapphire and nitride semiconductor materials.
Solution Approach 2:
The patent changes the substrate temperature parameter to 1000-1100°C for growing the t-BN buffer layer, which is optimal for forming a high-quality interface between the sapphire substrate and the subsequent wurtzite-structure AlGaInBN layer. This temperature parameter change enables single-crystal growth by providing sufficient thermal energy for atomic rearrangement while avoiding excessive thermal stress that would degrade crystal quality.
3Adaptability or versatility
If conventional buffer layers are used, then nitride semiconductor can be grown on sapphire substrate, but transferring films to flexible or inexpensive substrates is difficult
Solution Approach 1:
The graphite-type boron nitride (t-BN) buffer layer serves as a transferable intermediary that can be mechanically separated from the sapphire substrate along with the wurtzite-structure AlGaInBN layer. The t-BN layer maintains its structural integrity during transfer, enabling the nitride semiconductor film to be moved to flexible or inexpensive substrates such as plastic, glass, or metal substrates, thereby improving adaptability and ease of manufacture.
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 simplifies the growth process, reduces costs, and enables the transfer of high-quality wurtzite-structure GaN thin films to various substrates, including flexible and inexpensive ones, improving device characteristics and light emission efficiency while avoiding damage and thermal issues.
Implementation Method 1
a buffer layer including a hexagonal boron nitride (h-BN) thin film is formed on a sapphire substrate
Implementation Method 2
a wurtzite-structure AlxGa1-xN thin film is formed on the hexagonal boron nitride film
Implementation Method 3
using a graphite-type boron nitride buffer layer with van der Waals bonds
Data Source
Figure 1
Figure 2A~2B
Figure 3
AI summary
A nitride semiconductor structure of the present invention is obtained by growing an h- or t-BN thin film (12) and a wurtzite-structure AlxGa1-xN (x>0) thin film (14) as buffer layers and forming a single-crystal wurtzite-structure AlGaInBN thin film (13) thereon. While GaN, AlGaN, AlN, and the like have the wurtzite structure with sp3 bonds, h-BN or t-BN has the graphite structure with sp2 bonds, and has a completely different crystal structure. Accordingly, it has heretofore not been considered that a wurtzite-structure AlGaInBN thin film can be grown on a graphite-structure h-BN thin film. However, when a wurtzite-structure AlxGa1-xN (x>0) thin film (14) is formed as a buffer layer on a graphite-structure boron nitride thin film (12), a wurtzite-structure AlGaInBN (13) nitride semiconductor structure such as GaN can be grown on the buffer layer.