Multijunction LED Stacks With Tunnel Junctions for Efficiency Droop
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Solution Overview
Problem
LED efficiency is compromised at high drive-currents due to resistive losses and material-related challenges such as Auger recombination and carrier confinement losses, necessitating improved materials and device designs.
Innovation Solution
A multijunction light emitting diode (LED) structure incorporating tunnel junctions and multiple stacks with specific alloy compositions and quantum well configurations, allowing for increased efficiency by reducing current requirements and enhancing voltage matching with system components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If high drive-current is used to increase light output, then brightness is improved, but efficiency is worsened due to resistive losses and Auger recombination
Solution Approach 1:
The LED device is divided into multiple independent light-emitting stacks (first stack, second stack, etc.) connected in series through tunnel junctions. Each stack operates at a lower current density, avoiding the efficiency droop that occurs at high currents in single-junction LEDs. This segmentation allows the device to achieve high total light output while maintaining high efficiency in each individual stack.
2Loss of energy
If multiple stacks are connected in series to reduce current requirements, then efficiency is improved, but device complexity is worsened
Solution Approach 1:
Multiple LED stacks are merged into a single integrated device structure with shared substrate and contact layers. The stacks are connected in series through thin tunnel junctions that are integrated within the same growth structure, rather than being separate components. This merging approach reduces overall device complexity compared to connecting separate LEDs in series, while still achieving the efficiency benefits of reduced current operation.
3Reliability
If tunnel junctions are introduced to connect stacks, then current distribution is improved, but manufacturing complexity is worsened
Solution Approach 1:
The tunnel junctions are formed by modifying the doping parameters and layer thickness in the AlGaAs barrier layers that connect the GaInAs quantum well stacks. By adjusting these growth parameters during MOCVD fabrication, the tunnel junctions are created as an integral part of the standard LED growth process, rather than requiring separate fabrication steps. This approach maintains ease of manufacture while achieving reliable current distribution across multiple stacks.
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 multijunction LED design enhances quantum efficiency and reduces resistive losses, achieving greater than 50% efficiency at 500 mA/cm2 and facilitating easier integration into low power circuits by matching operating voltage with other system components.
Implementation Method 1
a tunnel junction, with the tunnel junction positioned between the p-type cladding layer of the first stack and the n-type cladding layer of the second stack
Implementation Method 2
at least one quantum well
Implementation Method 3
The device is capable of emitting light having a wavelength between 880 nm and 1300 nm
Data Source
AI summary
The present disclosure relates to a device that includes a first stack and a second stack, with each stack including, in order: an n-type cladding layer constructed of an alloy selected from at least one of GaInP, AlGaAs, GaInAsP, and/or AlGaInP, an n-type outer barrier layer constructed of at least one of GaAs and/or GaP; at least one quantum well; a p-type outer barrier layer constructed of at least one GaAs or GaP; and a p-type cladding layer constructed an alloy selected from at least one of GaInP, AlGaAs, GaInAsP, and/or AlGaInP; and a tunnel junction.