Columnar Nitride Semiconductor Crystals for Low Dislocation Density
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The existing methods for growing nitride-base compound semiconductor layers on sapphire substrates result in high threading dislocation densities, leading to inadequate crystallinity and light emitting characteristics, and are costly due to complex processes and high costs of low-dislocation-density GaN wafers, with challenges in forming electrodes on columnar crystals for large-area light emitting elements.
Innovation Solution
A method using molecular beam epitaxy or metal-organic vapor phase deposition to grow columnar crystals with controlled anisotropy in the c-axis direction, suppressing lateral growth and transitioning to isotropic growth at a predetermined height, allowing the formation of reverse truncated pyramids for continuous thin films and reducing threading dislocation density, while using efficient growth conditions to prevent electrode material deposition between adjacent crystals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If general MOCVD process is used to grow GaN film on sapphire substrate, then manufacturing process is simple, but threading dislocation density is high (10^9/cm^2)
Solution Approach 1:
The patent divides the continuous film growth into discrete columnar crystal growth stages. By forming isolated columnar crystals that grow vertically to a predetermined height and then fuse laterally, the process segments the growth into controlled phases, achieving low dislocation density (10^6/cm^2) while maintaining manufacturing feasibility through standardized process parameters.
Solution Approach 2:
The patent transitions from conventional two-dimensional lateral epitaxial growth to three-dimensional vertical columnar growth followed by lateral fusion. This dimensional change allows dislocations to be confined within individual columns during vertical growth, then eliminated during the fusion stage, resolving the contradiction between process simplicity and dislocation reduction.
2Manufacturing precision
If lateral epitaxial growth on mask is used to reduce threading dislocation density, then dislocation density is low (10^6/cm^2), but manufacturing process becomes complicated with more steps and higher costs
Solution Approach 1:
The patent extracts the mask formation step from the conventional lateral growth process. By directly growing columnar crystals on the substrate without requiring complex mask patterns, the method achieves low dislocation density through vertical growth and fusion, eliminating the need for mask fabrication, alignment, and removal steps, thus simplifying the manufacturing process while maintaining high precision.
Solution Approach 2:
The columnar crystals self-organize and self-limit their growth through the predetermined height control mechanism. The crystals automatically fuse laterally when they reach the target height, eliminating the need for external mask guidance and complex process control, thereby reducing manufacturing complexity while achieving low dislocation density.
3Ease of manufacture
If conventional electrode formation is used on columnar crystals, then electrode material can be deposited, but material deposits around side faces causing short-circuits and connection failures
Solution Approach 1:
The patent utilizes the curved side faces of the columnar crystals to redirect electrode material deposition. The curvature causes deposited material to follow the crystal contours and accumulate at the top surface rather than adhering to the vertical side walls, preventing short-circuits between adjacent columns while ensuring reliable electrical connection at the crystal tops.
Solution Approach 2:
The patent creates asymmetric electrode deposition patterns by controlling material to preferentially deposit on the top surfaces of columnar crystals rather than their side faces. This asymmetry is achieved through the specific growth geometry and deposition conditions, ensuring electrodes form only where needed for electrical connection while avoiding harmful deposition on lateral surfaces.
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 production of high-luminance light emitting elements with low threading dislocation density at reduced costs, simplifying the manufacturing process and ensuring effective electrode formation by preventing electrode material deposition around the columnar crystals.
Implementation Method 1
forming, on a substrate, columnar crystals of a nitride-base or an oxide-base compound semiconductor, by the molecular beam epitaxy (MBE) process
Implementation Method 2
or under different conditions by the MOCVD (metal-organic vapor phase deposition) process
Implementation Method 3
the columnar crystals are grown while ensuring anisotropy in the direction of c-axis, by controlling ratio of supply of Group-III atoms and nitrogen, or Group-II atoms and oxygen atoms
Implementation Method 4
growth of the nitride-base compound semiconductor layer onto the sapphire substrate results in an insufficient crystallinity as a continuous thin film
Data Source
AI summary
A method of manufacturing a semiconductor element by forming, on a substrate, columnar crystals of a nitride-base or an oxide-base compound semiconductor, and by using the columnar crystals, wherein on the surface of the substrate, the columnar crystals are grown while ensuring anisotropy in the direction of c-axis, by controlling ratio of supply of Group-III atoms and nitrogen, or Group-II atoms and oxygen atoms, and temperature of crystal growth, so as to suppress crystal growth in the lateral direction on the surface of the substrate.