3D GaN Pillar Structures for Enhanced Light Extraction
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Solution Overview
Problem
The high cost and inefficiency of producing high-quality gallium nitride (GaN) for LED devices due to high-temperature growth processes, substrate mismatch, and limited light emission caused by the high index of refraction of GaN, which results in threading dislocations and reduced quantum efficiency.
Innovation Solution
A method for fabricating three-dimensional GaN structures with planar surfaces using a combination of damage etching and wet etching techniques to form cavities and pillars, reducing defect density and enhancing light extraction by creating micro-rod or pillar LEDs with controlled crystallographic orientations, eliminating the need for additional surface texturing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If high-temperature growth processes (MOCVD/MBE) are used to produce GaN on substrates with different CTE, then GaN film can be grown with desired thickness and composition, but threading dislocations form that adversely affect device performance and reliability
Solution Approach 1:
The invention segments the GaN structure into multiple quantum well layers separated by barrier layers, creating a multi-layered quantum well structure. This segmentation allows stress to be distributed across multiple interfaces rather than accumulating in a single continuous layer, reducing threading dislocation formation while maintaining film quality and desired thickness
Solution Approach 2:
The invention changes the compositional parameters by introducing aluminum gallium nitride (AlGaN) barrier layers with varying aluminum content between the gallium nitride quantum wells. This parameter change in composition allows control over the lattice mismatch and stress distribution, enabling high-quality film growth with reduced dislocations while maintaining the desired GaN properties
2Ease of manufacture
If planar LED structure is used, then fabrication is simple following conventional MOCVD sequence, but light extraction is limited due to high index of refraction of GaN confining light to narrow angular cone
Solution Approach 1:
The invention introduces vertical dimensionality by creating three-dimensional micro-rod or pillar structures from the planar quantum well layers. This dimensional transformation from 2D planar to 3D vertical structures increases the emission surface area and modifies light extraction pathways, allowing light to escape from multiple surfaces (top and lateral) rather than being confined to a single planar interface, thereby improving extraction efficiency while maintaining fabrication simplicity
3Reliability
If film stress limits are considered in GaN growth, then threading dislocation density is reduced, but the amount of dopants that can be incorporated is limited which restricts range of emission characteristics
Solution Approach 1:
The invention segments the doped structure into alternating undoped GaN quantum wells and doped AlGaN barrier layers. This segmentation allows dopants to be concentrated in the barrier layers rather than distributed throughout the entire structure, reducing stress-induced dislocations in the quantum wells while still achieving the desired doping levels and emission characteristics through the barrier layer composition and thickness control
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 improves the internal quantum efficiency and light extraction of GaN LEDs by reducing defect density and increasing the emission area, while avoiding the limitations of conventional planar structures and high-temperature growth processes.
Implementation Method 1
The cavities are wet etched, forming planar sidewalls extending into the GaN film
Implementation Method 2
The cavities are formed using a laser ablation, ion implantation, sand blasting, or dry etching process
Data Source
AI summary
A method is provided for fabricating three-dimensional gallium nitride (GaN) pillar structures with planar surfaces. After providing a substrate, the method grows a GaN film overlying a top surface of the substrate and forms cavities in a top surface of the GaN film. The cavities are formed using a laser ablation, ion implantation, sand blasting, or dry etching process. The cavities in the GaN film top surface are then wet etched, forming planar sidewalls extending into the GaN film. More explicitly, the cavities are formed into a c-plane GaN film top surface, and the planar sidewalls are formed perpendicular to a c-plane, in the m-plane or a-plane family.