LED with Segmented Active Regions for Green Emission
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Solution Overview
Problem
Conventional light emitting diodes (LEDs), particularly those based on gallium nitride (GaN)/indium gallium nitride (InGaN), exhibit low quantum efficiencies in longer wavelength ranges such as green due to electrical current 'droop' caused by mechanisms like Auger recombination, hole injection inefficiencies, and carrier bypassing through crystal defects and dislocations.
Innovation Solution
The design incorporates a light emitting device structure with a first active region for blue or violet emission and a second active region for green emission via photoluminescence, where carrier density is controlled by adjusting the number of quantum wells, and the second active region is spaced apart to minimize carrier bypassing and leakage currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional GaN/InGaN LEDs are used for green wavelength emission, then the device structure is simple, but the quantum efficiency is low due to electrical current droop
Solution Approach 1:
The light emitting device is divided into multiple active regions with different functions: a first active region for generating blue/violet light via electroluminescence, and a second active region for generating green light via photoluminescence. This segmentation allows each region to be optimized for its specific function, resolving the contradiction between structural simplicity and quantum efficiency by distributing complexity across specialized components.
Solution Approach 2:
A transparent conductive layer is introduced as an intermediary between the first and second active regions. This layer facilitates the transmission of blue/violet light from the first region to excite the second region, while also serving as an electrical contact. The intermediary enables efficient energy transfer and addresses the quantum efficiency problem without requiring direct contact between the active regions.
2Device complexity
If the second active region is placed close to the first active region, then the device structure is compact, but carrier bypassing through crystal defects and dislocations increases
Solution Approach 1:
The transparent conductive layer serves as a spatial and functional intermediary between the first and second active regions. It maintains an optimal distance that prevents carrier bypassing through crystal defects while still allowing efficient optical coupling. This intermediary structure resolves the contradiction by providing both electrical functionality and spatial separation.
Solution Approach 2:
The device structure implements local quality by having different regions with distinct properties: the first active region is optimized for electroluminescence with specific carrier injection characteristics, while the second active region is optimized for photoluminescence with appropriate absorption characteristics. The transparent conductive layer has specific optical and electrical properties tailored for its intermediary function. This local optimization allows compact design while maintaining reliability.
3Illumination intensity
If high current density is applied to achieve higher output power, then the illumination intensity increases, but Auger recombination increases causing quantum efficiency to drop
Solution Approach 1:
The device replaces direct electrical injection into the green emission region with optical excitation. Instead of injecting carriers directly into the second active region (which would cause Auger recombination at high currents), blue/violet light from the first region excites the second region via photoluminescence. This substitution of electrical injection with optical pumping eliminates the Auger recombination problem while maintaining high output power capability.
Solution Approach 2:
The device separates the carrier injection function (first active region) from the green light emission function (second active region). By segmenting these functions into different regions with different excitation mechanisms, the device can operate at high current densities in the first region without suffering from Auger recombination losses in the green emission process.
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 configuration enhances quantum efficiency and wavelength stability for green emission, surpassing conventional LEDs by reducing Auger recombination and carrier bypassing issues, resulting in higher output power and efficiency in longer wavelength ranges.
Implementation Method 1
a first active region for blue or violet emission
Implementation Method 2
a second active region for green emission via photoluminescence
Implementation Method 3
carrier density is controlled by adjusting the number of quantum wells
Data Source
AI summary
Various embodiments of light emitting devices with high quantum efficiencies are described herein. In one embodiment, a light emitting device includes a first contact, a second contact spaced apart from the first contact, and a first active region between the first and second contacts. The first active region is configured to produce a first emission via electroluminescence when a voltage is applied between the first and second contacts, and the first emission having a first center wavelength. The light emitting device also includes a second active region spaced apart from the first active region. The second active region is configured to absorb at least a portion of the first emission and produce a second emission via photoluminescence, and the second emission having a second center wavelength longer than the first center wavelength.