GaN Mesa Bilayer Porosification for Uniform Micro-LED Substrates
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Solution Overview
Problem
Current methods for porosifying GaN mesas in micro-LEDs face challenges in achieving uniform porosification across large substrates, leading to edge/centre effects and incomplete porosification due to degradation in lateral conductivity and miscibility issues with InGaN materials.
Innovation Solution
A method involving a bilayer structure with different doping levels of GaN, where a lightly doped layer serves as electrical contact and remains integral, while a heavily doped layer is porosified, using an electrolytic solution and voltage to achieve uniform porosification of (Al,In,Ga)N/(Al,In,Ga)N mesas, reducing stress and enhancing crystalline quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single doped GaN layer is used for porosification, then the process is simple, but uniform porosification across large substrates cannot be achieved due to edge/centre effects
Solution Approach 1:
The single doped GaN layer is segmented into two distinct layers with different doping concentrations: a first doped GaN layer (1×10^18 to 1×10^19 atoms/cm³) and a second heavily doped GaN layer (1×10^19 to 1×10^20 atoms/cm³). This segmentation allows the second layer to provide sufficient lateral conductivity for uniform porosification across large substrates while the first layer maintains structural integrity, thereby resolving the contradiction between process simplicity and porosification uniformity.
Solution Approach 2:
Different regions of the GaN structure are assigned different doping qualities: the first doped GaN layer has lower doping concentration (1×10^18 to 1×10^19 atoms/cm³) to remain integral during porosification, while the second heavily doped GaN layer has higher doping concentration (1×10^19 to 1×10^20 atoms/cm³) to enable complete and uniform porosification. This local quality differentiation resolves the contradiction by optimizing each layer's properties for its specific function.
2Stress or pressure
If the doped GaN layer is fully porosified to reduce stress, then stress relaxation is improved, but lateral conductivity degrades leading to edge/centre effects
Solution Approach 1:
The GaN layer is segmented into two layers with different doping concentrations: the first doped GaN layer (1×10^18 to 1×10^19 atoms/cm³) maintains sufficient lateral conductivity after partial porosification, while the second heavily doped GaN layer (1×10^19 to 1×10^20 atoms/cm³) is fully porosified to provide stress relaxation. This segmentation resolves the contradiction between stress reduction and conductivity maintenance.
Solution Approach 2:
Different regions of the GaN structure are assigned different porosification qualities: the first doped GaN layer is partially porosified to maintain lateral conductivity, while the second heavily doped GaN layer is fully porosified to maximize stress relaxation. This local quality differentiation resolves the contradiction by optimizing porosification extent for each layer's function.
3Adaptability or versatility
If InGaN concentration is increased to emit red light, then wavelength coverage is improved, but material quality degrades due to low miscibility and high compressive stress
Solution Approach 1:
The GaN layer is segmented into two layers with different doping concentrations to enable controlled porosification. The second heavily doped GaN layer is fully porosified to relax compressive stress, while the first doped GaN layer is partially porosified to maintain structural integrity. This stress relaxation enables higher InGaN indium concentration (up to 35% for red emission) without degrading material quality, thus resolving the contradiction between wavelength coverage and crystalline quality.
Solution Approach 2:
Different regions of the GaN structure are assigned different porosification qualities to optimize stress distribution. The second heavily doped GaN layer undergoes complete porosification to maximize stress relaxation for high-indium InGaN layers, while the first doped GaN layer undergoes partial porosification to maintain structural support. This local quality differentiation enables high InGaN indium concentration with maintained material quality.
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 allows for complete and uniform porosification of mesas on large substrates, reducing edge/centre effects and improving the quality of InGaN LED structures by relaxing stress and enhancing epitaxy control, enabling the production of high-definition micro-LEDs with reduced alignment issues.
Implementation Method 1
The porosification step is implemented by polarising the heavily doped (Al,In,Ga)N layer with an anodic potential in an electrolytic solution
Implementation Method 2
The porosification step is implemented by polarising the heavily doped (Al,In,Ga)N layer with an anodic potential in an electrolytic solution
Data Source
AI summary
Method for porosifying mesas comprising the following steps:providing a structure (100) comprising a substrate (110) covered with (Al,In,Ga)N/(Al,In,Ga)N mesas (120),the substrate (110) comprising a support layer (114), a first layer of non-doped GaN (111) and a second layer of doped GaN (112),the mesas (120) comprising a third layer of heavily doped (Al,In,Ga)N(123) and a fourth layer of non-doped or lightly doped (Al,In,Ga)N(124),a part (112b) of the second layer (112) of doped GaN being extended in the mesas (120) or a part (123a) of the third layer (123) of heavily doped (Al,In,Ga)N being extended in the base substrate (110),immersing the structure (100) and a counter-electrode in an electrolytic solution,applying a voltage or a current between the structure (100) and the counter-electrode so as to porosify the third layer (123) of heavily doped (Al,In,Ga)N of the mesas (120).