Off-Cut Sapphire Substrate for M-Plane GaN Growth
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Solution Overview
Problem
Current methods for growing m-plane nitride semiconductor luminescent elements are cumbersome and require expensive substrates like SiC or LiAlO2, while existing vapor phase methods fail to achieve m-plane growth using inexpensive sapphire substrates, limiting the enhancement of electrical characteristics and radiative recombination efficiency.
Innovation Solution
A method involving a sapphire substrate with a predetermined small off-angle cut from the m-plane is used for crystal growth, allowing c-axis GaN to grow on a-plane steps and m-plane terraces in a vapor phase method, integrating steps to form an m-plane GaN single crystal, which increases wave function overlap and reduces piezoelectric field influence, enhancing radiative recombination efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If expensive SiC or LiAlO2 substrates are used for m-plane growth, then m-plane GaN crystal growth is achieved, but substrate cost increases significantly
Solution Approach 1:
The patent replaces expensive SiC or LiAlO2 substrates with inexpensive sapphire substrates for m-plane GaN crystal growth. By introducing a specific off-angle cut (0.5-10 degrees from m-plane) and using a nucleation layer, the invention enables high-quality m-plane GaN growth on cheap sapphire substrates, eliminating the need for costly disposable substrates while maintaining crystal growth quality
Solution Approach 2:
The patent changes the substrate orientation parameter by introducing an off-angle cut from the standard m-plane. This parameter change (creating a-plane steps at a specific angle) enables the sapphire substrate to support m-plane GaN growth instead of requiring expensive substrates, thereby reducing cost while achieving the desired crystal orientation
2Manufacturing precision
If solvothermal method is used for ZnO seed crystal growth, then m-plane crystal growth is achieved, but the fabrication process becomes cumbersome and complicated
Solution Approach 1:
The patent extracts and eliminates the intermediate solvothermal seed crystal growth step from the fabrication process. By directly forming a nucleation layer on the off-cut sapphire substrate and growing GaN crystals in a single vapor phase process, the invention removes the need to temporarily take out the substrate for separate processing, thereby simplifying the overall fabrication process
Solution Approach 2:
The patent merges the substrate preparation and crystal growth steps into a single continuous vapor phase process. Instead of separate solvothermal seed growth followed by MOCVD device fabrication, the invention combines these operations by forming the nucleation layer and growing the GaN crystal structure in one continuous process, eliminating process interruptions and simplifying fabrication
3Ease of manufacture
If m-plane GaN is grown using conventional vapor phase method on standard sapphire substrate, then process simplicity is maintained, but only semipolar GaN is obtained instead of m-plane GaN
Solution Approach 1:
The patent performs preliminary action by pre-cutting the sapphire substrate with a specific off-angle (0.5-10 degrees from m-plane) before crystal growth. This preliminary substrate preparation creates the necessary a-plane steps that guide the vapor phase growth to form m-plane GaN crystals, ensuring the correct crystal plane orientation is achieved without complicating the subsequent growth process
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 m-plane GaN crystals and luminescent elements with improved internal quantum efficiency using inexpensive sapphire substrates, overcoming the limitations of previous methods by integrating steps and controlling the growth surface to minimize defects and nitridation.
Implementation Method 1
a c-plane of GaN is allowed to grow from each step plane formed as an a-plane onto a terrace in a vapor phase method, such as an MOCVD method
Implementation Method 2
an epitaxially-grown excellent GaN single crystal continues to grow, so that the m-plane thereof is opposite to the surplane of the terrace
Implementation Method 3
the respective steps become integrated (fused) with one another. Thus, it is possible to grow an m-plane GaN single crystal
Data Source
AI summary
The present invention provides an inexpensive substrate which can realize m-plane growth of a crystal by vapor phase growth. In a sapphire substrate, an off-angle plane slanted from an m-plane by a predetermined very small angle is prepared as a growth surface, which is a template of the crystal, at the time of growing a crystal of GaN or the like, by a polishing process to prepare a stepwise substrate comprising steps and terraces. According to the above-described configuration, even if an inexpensive sapphire substrate, which normally does not form an m-plane (nonpolar plane) GaN film, is used as a substrate for crystal growth, the following advantages can be attained. Specifically, c-axis growth can be carried out from the plane of each step as an a-plane on the terrace by vapor phase growth, which is advantageous in the fabrication of a device, in order to grow an excellent GaN single crystal which has been epitaxially grown so that the m-plane is opposite to the surplane of the terrace, and, in the mean time, the steps become integrated (fused), whereby a device can be fabricated from a substrate of a GaN single crystal having no significant threading dislocation. Further, the use of the m-plane can advantageously eliminate the influence of piezo electric fields.