GaN LED Fabrication with Inverted Pyramid Rough Side Walls
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Solution Overview
Problem
The light-emitting efficiency of gallium nitride (GaN) LEDs is limited due to significant light reflection and energy loss when light is emitted from the semiconductor layer to air, leading to increased heat dissipation burdens, and existing surface roughening techniques are complex, costly, and insufficiently effective.
Innovation Solution
A fabrication method involving heat treatment of substrates with hydrogen or mixed gases, followed by growth of specific buffer and quantum-well layers, and subsequent wet etching to form an inverted pyramid structure with a rough side wall, changing growth conditions to transition from three-dimensional to two-dimensional GaN growth and doping Si near the quantum-well layer to enhance light emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If surface roughening technology is applied to improve light-emitting efficiency, then light extraction is enhanced, but process complexity and cost increase
Solution Approach 1:
The patent applies preliminary action by forming the rough surface structure during the epitaxial growth process itself, before chip fabrication. The growth parameters (temperature, pressure, rotation rate) are dynamically adjusted during layer deposition to create the desired rough morphology, eliminating the need for subsequent complex surface treatment processes.
Solution Approach 2:
The epitaxial growth process serves dual purposes: it both deposits the functional semiconductor layers and simultaneously creates the rough surface structure for light extraction enhancement. The system uses its own growth mechanisms to achieve the surface modification, without requiring external processing steps.
2Illumination intensity
If conventional surface roughening is applied, then some light extraction improvement is achieved, but the roughening area is limited to chip grain surface resulting in insufficient overall improvement
Solution Approach 1:
The patent extends the rough surface formation from the traditional top surface only to include the side surfaces of the chip grains. By controlling epitaxial growth conditions, the rough morphology is developed in multiple dimensions, significantly increasing the total surface area available for light extraction while maintaining process simplicity.
3Illumination intensity
If light is emitted from semiconductor layer to air, then light emission occurs, but large refractive index difference causes complete reflection and energy loss
Solution Approach 1:
The patent applies local quality by creating regions with different surface properties. The rough surface structures are formed in specific locations (top and side surfaces) to locally modify light extraction characteristics, while the bulk semiconductor material maintains its original properties. This localized approach reduces overall energy loss without requiring complete material replacement.
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 method significantly improves light-emitting efficiency by forming an inverted pyramid structure with a rough side wall, enhancing light extraction without adding epitaxy or chip fabrication steps, thus reducing heat dissipation and increasing commercial viability.
Implementation Method 1
take heat treatment for the substrate with hydrogen or with mixed gas of hydrogen, nitrogen and ammonia gas
Implementation Method 2
grow a low-temperature AlxGa1-xN (0≦x≦1) buffer layer, an undoped gradient GaN layer, an N-type gradient GaN layer, a multiple quantum-well layer, an AlxGa1-xN (0≦x≦1) electron blocking layer and a P-type layer over the substrate after heat treatment
Implementation Method 3
set the growth pressure from high to low and temperature and rotation rate from low to high to realize change from three-dimensional growth to two-dimensional growth of the GaN structure layer
Implementation Method 4
Si is doped at position approximate to the multiple quantum-well layer to form an undoped gradient GaN layer and an N-type gradient GaN layer with gradient growth mode
Implementation Method 5
immerse them in chemical solutions for wet etching; and form an inverted pyramid structure with rough side wall over the multiple quantum-well layer
Data Source
AI summary
A LED fabrication method includes: providing a substrate; forming a low-temperature AlxGa1-xN (0≦x≦1) layer over the growth substrate; setting the growth pressure from high to low and temperature and rotation rate from low to high to realize change from three-dimensional growth to two-dimensional growth of the GaN structure layer before growth of the multiple quantum-well layer, in which, Si is doped at position approximate to the multiple quantum-well layer to form an undoped gradient GaN layer and an N-type gradient GaN layer; growing a multiple quantum-well layer, an AlxGa1-xN (0≦x≦1) layer and a P-type layer; and during later chip fabrication, dividing the epitaxial wafer over the etched N-type platform into chip grains and immersing them in chemical solutions for wet etching; and forming an inverted pyramid structure with rough side wall over the multiple quantum-well layer to improve light-emitting efficiency.