Core-Shell μLED Structure for Quantum-Confined Stark Effect Mitigation
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Solution Overview
Problem
Achieving high-efficiency, high-brightness, and stable micro-light emitting diodes (μLEDs) with dimensions as small as one micrometer for applications like virtual and augmented reality has been challenging due to efficiency cliffs caused by surface damage and quantum-confined Stark effects, especially for long wavelength LEDs.
Innovation Solution
The development of a light emitting device with a silicon substrate, a core-shell structure, and polarization doping, featuring strain compensation barriers and a negative Al composition gradient in the AlGaN shell to mitigate piezoelectric field issues and enhance indium incorporation, resulting in stable operation and negligible quantum-confined Stark effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If conventional quantum well LED structures are shrunk to micrometer or submicron scale, then device size is reduced for VR/AR applications, but external quantum efficiency drops to well below 1% due to surface damage and nonradiative surface recombination
Solution Approach 1:
The device is segmented into distinct functional regions: a top-down etched broad area LED structure is divided into multiple micrometer or submicron scale micro-LED arrays. Each micro-LED is further segmented into quantum well active regions separated by barrier layers. This segmentation allows the large area structure to be divided into smaller efficient emitting units, maintaining high external quantum efficiency while achieving the required small device size for VR/AR applications.
Solution Approach 2:
Different regions of the device are given different local qualities: the active regions use specific quantum well compositions and thicknesses optimized for high efficiency emission, while barrier regions use different compositions to prevent carrier leakage. The contact regions have specialized doping and metallization for optimal electrical injection. This local optimization ensures each part performs its function at maximum efficiency, preventing the efficiency cliff that occurs when uniformly scaling down conventional structures.
2Length of moving object
If top-down etching is used to create micrometer scale LEDs, then device dimensions are reduced, but surface damage and nonradiative surface recombination increase causing efficiency cliff
Solution Approach 1:
The patent applies beforehand cushioning by implementing multiple protective measures before the harmful effects of surface damage can manifest: (1) Careful control of the top-down etching process parameters to minimize surface damage accumulation, (2) Application of passivation layers to chemically passivate surface states and reduce nonradiative recombination centers, (3) Optimization of quantum well structures to confine carriers away from damaged surfaces. These preventive measures cushion against the efficiency cliff that would otherwise occur due to surface damage in etched micro-LEDs.
3Illumination intensity
If long wavelength LEDs are fabricated, then emission wavelength is extended for full-color emission, but efficiency and stability deteriorate due to enhanced defect formation from large misfit between InN and GaN
Solution Approach 1:
The patent employs parameter changes to achieve long wavelength emission while maintaining reliability: (1) Precise control of indium composition parameters in InGaN quantum wells to optimize wavelength without excessive lattice mismatch, (2) Adjustment of quantum well thickness parameters to balance emission wavelength and carrier confinement, (3) Modification of barrier layer composition and thickness parameters to compensate for strain and prevent defect formation. These parameter optimizations allow full-color emission capability while preventing the efficiency and stability deterioration that occurs with high indium content materials.
4Illumination intensity
If long wavelength LEDs are fabricated, then emission spectrum is extended, but performance suffers from quantum-confined Stark effect
Solution Approach 1:
The patent uses intermediary structures to mitigate the quantum-confined Stark effect: (1) Insertion of polarization-compensating barrier layers between quantum wells that act as intermediaries to screen internal electric fields, (2) Use of graded composition buffer layers as intermediaries to gradually transition between materials with different piezoelectric properties, reducing abrupt field effects. These intermediary structures enable extended emission spectrum while preventing the performance degradation caused by quantum-confined Stark effect in long wavelength devices.
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 enables the creation of high-performance μLEDs with stable wavelength emissions and reduced thermal accumulation, suitable for integration with CMOS electronics, addressing the efficiency challenges and achieving ultrahigh resolution in emerging applications.
Implementation Method 1
a shell comprising a gradient configuration with piezoelectric field compensation characteristics
Implementation Method 2
an active region, a shell comprising a gradient configuration with piezoelectric field compensation characteristics
Data Source
AI summary
Systems and methods presented herein include efficient and effective Light Emitting Devices (LED) devices. In one embodiment, a light emitting device comprises: a substrate comprising silicon; a first portion comprising a group III-V compound component with a first type of doping; a second portion comprising an active region, a shell comprising a gradient configuration with piezoelectric field compensation characteristics; and a third portion comprising a group III-V compound component with a second type of doping, The silicon substrate is coupled to the first portion. The first portion and shell are coupled to the second portion with is in turn coupled to the third portion. The active region comprises a quantum core structure with strain compensation barriers and polarization doping. The strain compensated barriers form multiple quantum wells. In one embodiment, the strain compensation barriers include AlGaN in a configuration that compensates tensile strain within the active region. The AlGaN can also be configured to induce polarization charges and enhance indium incorporation. In one embodiment, the shell comprises AlGaN with a negative Al composition gradient.