LED Sidewall Passivation Layer for Higher Micro-LED Quantum Efficiency
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Solution Overview
Problem
Group III-nitride LEDs face challenges with surface recombination due to crystal defects and the termination of the periodic crystal structure, leading to reduced internal quantum efficiency (IQE).
Innovation Solution
A light-emitting diode (LED) precursor is developed with a passivation layer comprising crystalline Group III-nitride with a higher bandgap than the active layer, covering the sidewalls to prevent trap site formation and charge carrier leakage, and aligning the sidewalls with non-polar crystal planes to avoid two-dimensional electron gas formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the LED size is reduced to create micro LED arrays, then the luminance and power density are improved, but the surface area to volume ratio increases leading to enhanced surface recombination and reduced internal quantum efficiency
Solution Approach 1:
A passivation layer is introduced as an intermediary between the active layer and the external environment. This passivation layer specifically targets and neutralizes surface defects and trap sites at the sidewalls of the micro LED, preventing non-radiative recombination without interfering with the radiative recombination process in the bulk active region. The passivation layer acts as a protective mediator that allows the micro LED to maintain high luminance while suppressing surface recombination losses.
2Reliability
If conventional LED structures are used without passivation, then the device complexity is low, but non-radiative recombination at surface defects reduces internal quantum efficiency
Solution Approach 1:
The passivation layer modifies the surface properties of the micro LED sidewalls by changing the electrical and chemical parameters at the surface. Specifically, it alters the surface potential, carrier concentration, and defect density at the sidewall interface, transforming the surface from a high-recombination region to a low-recombination region. This parameter change approach effectively suppresses non-radiative recombination without requiring fundamental structural redesign.
3Reliability
If sidewalls are not passivated, then the manufacturing process is simple, but trap sites and charge leakage paths reduce internal quantum efficiency
Solution Approach 1:
The passivation layer is applied in advance to the sidewall surfaces before final device assembly and operation. This preliminary passivation action prevents the formation and activation of trap sites during subsequent processing steps and operational stress. By performing the passivation early in the manufacturing sequence, the process actually simplifies overall fabrication by eliminating the need for complex in-situ surface treatments or post-processing surface repair steps.
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
The solution significantly reduces trap sites and charge leakage paths, enhancing the internal quantum efficiency of the LEDs by maintaining the periodic crystal structure and preventing non-radiative recombination events.
Implementation Method 1
The passivation layer comprises a crystalline Group III-nitride with a bandgap higher than a bandgap of the active layer
Implementation Method 2
Each layer of the Group III-nitride layers comprises a crystalline Group III-nitride. The passivation layer comprises a crystalline Group III-nitride
Implementation Method 3
Group III-nitride LEDs are inorganic semiconductor LEDs containing GaN and its alloys with InN and AlN in the active light-emitting region
Data Source
AI summary
A light emitting diode (LED) precursor is provided. The LED precursor comprises a substrate (10), an LED structure (30) comprising a plurality of Group III-nitride layers, and a passivation layer (40). The LED structure comprises a p-type semiconductor layer (36), an n-type semiconductor layer (32), and an active layer (34) between the p-type and n-type semiconductor layers. Each of the plurality of Group III-nitride layers comprises a crystalline Group III-nitride. The LED structure has a sidewall (37) which extends in a plane orthogonal to a (0001) crystal plane of the Group III-nitride layers. The passivation layer is provided on the sidewall of the LED structure such that the passivation layer covers the active layer. The passivation layer comprises a crystalline Group III-nitride with a bandgap higher than a bandgap of the active layer. The LED structure is shaped such that the sidewall of the LED structure is aligned with a non-polar crystal plane of each the Group III-nitride layers of the LED structure.