Group III Nitride Single Crystal Layer on Sapphire
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Solution Overview
Problem
The challenge is to achieve stable group III polarity growth and high light transmittance in ultraviolet ray emitting devices using group III nitride semiconductor crystals grown on sapphire substrates, as existing methods often result in poor crystal quality and low light transmittance due to mixed polarity domains and surface roughness.
Innovation Solution
A method involving a two-step metal-organic chemical vapor deposition process where an initial single crystal layer with controlled oxygen concentration is formed on a sapphire substrate, followed by a second layer with reduced oxygen concentration, promoting stable group III polarity growth and enhancing crystallinity and light transmittance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If group III nitride semiconductor crystal is grown on sapphire substrate using conventional MOCVD method, then light transmittance in ultraviolet range is improved, but crystal quality deteriorates due to mixed polarity domains and surface roughness
Solution Approach 1:
The crystal growth process is divided into two distinct stages: first growing an initial layer with mixed polarity to establish a foundation on the sapphire substrate, then growing a second layer with controlled group III polarity to achieve smooth surface and high crystallinity. This segmentation allows each stage to serve its specific function without compromising the other.
Solution Approach 2:
Different polarity characteristics are intentionally created in different regions/layers of the crystal structure. The initial layer contains mixed polarity domains suitable for substrate attachment, while the upper layer maintains uniform group III polarity for optimal optical properties and surface smoothness.
2Productivity
If N polarity growth is performed on sapphire substrate, then crystal growth proceeds, but surface roughness significantly deteriorates and polarity inversion domains are generated
Solution Approach 1:
Instead of attempting N polarity growth directly on sapphire substrate (which causes roughness), the invention inverts the approach by first creating an initial layer that establishes group III polarity orientation, then growing the main crystal layer in the group III polarity direction, which produces smooth surfaces and avoids polarity inversion domains.
3Manufacturing precision
If group III polarity growth is performed to obtain smooth crystal surface, then surface smoothness is improved, but control of growth condition becomes more difficult
Solution Approach 1:
The initial layer is grown first to pre-establish the group III polarity orientation and create a template structure on the sapphire substrate. This preliminary action simplifies subsequent growth conditions, as the polarity is already determined and surface smoothness is maintained throughout the second growth stage.
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 group III nitride semiconductor crystals with smooth surfaces and high crystallinity, improving the light emitting properties of ultraviolet devices by maintaining high light transmittance even in the ultraviolet range.
Implementation Method 1
a crystal growth of the group III nitride semiconductor thin film on the single crystal substrate using a chemical vapor deposition method such as the metal-organic chemical vapor deposition method (MOCVD method)
Implementation Method 2
a first growing step of supplying an oxygen source gas to the sapphire substrate with a raw material gas for growing the group III nitride single crystal, thereby growing the initial single crystal layer comprising the group III nitride and containing oxygen in a concentration of 1×1020 cm−3 or more and 5×1021 cm−3 or less
Data Source
AI summary
A layered body having a single crystal layer including a group III nitride having a composition AlxGayInzN (wherein, X, Y and Z are rational numbers respectively satisfying 0.9≦X≦1.0, 0.0≦Y≦0.1, 0.0≦Z≦0.1, and X+Y+Z=1.0) on a sapphire substrate. The layered body includes an initial single crystal layer that includes the group III nitride composition, an oxygen concentration of 1×1020 cm−3 or more and 5×1021 cm−3 or less and a thickness of 15 nm or more and 40 nm or less on the sapphire substrate and a second group III nitride single crystal layer including the group III nitride composition and having a reduced oxygen concentration than the initial single crystal layer.