Tunnel Junction μLED Hydrogen Diffusion for Low Resistance
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Solution Overview
Problem
GaN-based micro light-emitting diodes (μLEDs) face challenges due to poor conductive anode conductivity resulting from high resistance of the p-doped GaN layer, leading to degradation of wall-plug efficiency and current crowding, which is exacerbated by the low miscibility of Mg atoms and the formation of magnesium-hydrogen complexes, making it difficult to form good ohmic contacts.
Innovation Solution
The implementation of a tunnel junction in μLEDs, which is annealed after mesa etching, allows for hydrogen diffusion out of the p-doped semiconductor layer through exposed side walls, reducing resistivity and eliminating the need for a regrowth step, thereby improving current spreading and contact formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Mg-doped p-GaN layer is used to create the anode, then the p-n junction can be formed, but the high resistance of the p-doped layer degrades wall-plug efficiency and causes current crowding
Solution Approach 1:
The anode structure is segmented into multiple layers: a highly doped p++-GaN contact layer with thickness of 50-200 nm for low resistance contact, and a lightly doped p-GaN layer for carrier injection. This segmentation allows each layer to optimize its function - the contact layer minimizes resistance while the active layer maintains proper doping for light emission
Solution Approach 2:
Different doping concentrations are applied to different regions of the p-GaN layer. The contact region uses heavy p++ doping (10^19-10^20 cm^-3) to reduce resistance, while the light-emitting region uses lighter p doping (10^18-10^19 cm^-3) to maintain proper carrier injection and avoid excessive free carrier absorption
2Object-affected harmful factors
If Mg doping concentration is increased to reduce resistivity, then conductivity improves, but low miscibility of Mg atoms and Mg-H complex formation increase resistivity
Solution Approach 1:
A thin highly doped p++-GaN contact layer is deposited first before the main p-GaN layer. This preliminary highly doped layer provides immediate low-resistance contact path, allowing the subsequent lightly doped layer to be optimized for light emission without worrying about resistance issues
Solution Approach 2:
The tunnel junction acts as an intermediary structure between the p-GaN anode and the external circuit. It provides a low-resistance current path that bypasses the high-resistance p-GaN layer, effectively decoupling the electrical contact requirement from the light-emitting layer properties
3Object-affected harmful factors
If regrowth process is used to activate p-GaN, then conductivity improves, but processing complexity and cost increase
Solution Approach 1:
The highly doped p++-GaN contact layer is deposited with such high doping concentration that it self-activates upon deposition, providing immediate low-resistance contact without requiring subsequent regrowth or annealing steps. This preliminary action eliminates the need for complex post-processing
Solution Approach 2:
The activation step is extracted and eliminated from the process by using a deposition method that directly creates a highly conductive layer. The high doping concentration achieved during deposition bypasses the need for thermal activation that would otherwise be required to activate Mg dopants
4Reliability
If tunnel junction is implemented, then current spreading improves and forward voltage reduces, but additional processing steps are required
Solution Approach 1:
The tunnel junction structure is merged with the existing p-GaN contact layer structure. The highly doped p++-GaN layer serves dual functions as both the contact layer and the tunnel junction, eliminating the need for separate tunnel junction processing steps
Solution Approach 2:
The highly doped p++-GaN contact layer is designed to perform multiple functions: providing low-resistance ohmic contact, enabling tunnel junction current spreading, and serving as the anode contact. This multi-functionality reduces the number of separate components and processing steps required
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 enhances wall-plug efficiency, reduces forward voltage, increases light extraction efficiency, simplifies processing, and improves the reliability of ohmic contacts by facilitating easier contact formation on the n-GaN layer, all while eliminating the need for costly regrowth processes.
Implementation Method 1
allows for hydrogen diffusion out of the p-doped semiconductor layer through exposed side walls
Implementation Method 2
which is annealed after mesa etching
Data Source
AI summary
A light emitting diode (LED) is manufactured using a process in which hydrogen diffuses out of a p-doped semiconductor layer via an exposed side wall of the p-doped semiconductor layer. The process includes forming a light generation layer on a base semiconductor layer and forming the p-doped semiconductor layer on the light generation layer. A tunnel junction layer is formed on the p-doped semiconductor layer and a contact layer is formed on the junction layer. The process also includes etching through at least the contact layer, the tunnel junction layer, and the p-doped semiconductor layer to expose the side wall of the p-doped semiconductor layer and enabling hydrogen to diffuse out of the p-doped semiconductor layer at least partially through the exposed side wall.