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High Bandgap Phosphide Approaches for LED Applications

A new approach to fabricating high-efficiency Amber LEDs

National Renewable Energy Laboratory

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NREL's amber LED prototype.
NREL's amber LED prototype.

RGBA Color-Mixing
RGBA Color-Mixing

GaInP - AlInP Efficiency Comparison
GaInP - AlInP Efficiency Comparison

Technology Marketing Summary

NREL is closing the LED "green gap" with a patent-pending technology that allows for easy manufacturing of low-cost amber LEDs that—when combined with red, green, and blue LEDs—produce brilliant broad-spectrum white light more efficiently than current LEDs. This RGBA color-mixing technique enables low-cost, easy-to-manufacture white LEDs with improved luminosity.

This novel device architecture achieves nearly double the efficiency of current amber LEDs by increasing electron confinement with the employment of a disordered/ordered/disordered AlInP alloy composition. In addition, the color-mixing approach avoids the Stokes losses associated with producing white light via conventional (phosphor-converted blue) LEDs.

NREL's game-changing innovation could transform the market for solid-state lighting (SSL) for industry, businesses, and consumers. It also will impact the performance of lasers and photovoltaics.

Description

Light emitting diodes (LEDs) have seen increased commercialization and investment into R&D as energy efficiency begins to play a larger role in cutting emissions.  The U.S. Department of Energy expects to phase out tungsten bulbs by 2014, and compact fluorescents by 2020, leaving LEDs with virtually the entire lighting market. LED fixtures prices have also seen a 25% drop over the last two years, along with higher adoption in large commercial buildings and outdoor applications.  Market research predicts that the LED enterprise lighting market will surpass $1 billion annual revenue by 2014.  While the growth of the LED market has spurred many companies into different parts of the value chain, there are still technical hurdles that need to be addressed.  One of the most significant challenges is obtaining white light with LEDs.

Flexibility in color rendering index (CRI) for “white” light can be obtained using a RGB (red-green-blue) or RGBA (red-green-blue-amber) color-mixing with a set of three or four different LEDs, respectively.  While efficient red (or magenta) and blue (or cyan) LEDs are commercially available, green and amber LEDs with high quantum efficiencies remain elusive.  The ideal amber emission wavelength for a three-color mixing scheme is approximately 590 nm, which maximizes the CRI and relaxes the requirements for the red and blue emission as well. 

In most III-V semiconductor compounds and alloys that are lattice-matched to a readily obtainable bulk substrate occurs at energies below 2.4 eV.  NREL scientists have found a way to addresses the efficiency losses associated with inter-valley transfer incurred in most III-V material systems where green emission occurs at an energy range in the vicinity of the direct to indirect band gap crossover point.  Al1-xInxP is a promising material for amber LEDs due to its more favorable peak in the direct bandgap, undergoing a direct to indirect transition at 2.4 eV (x = 0.46, assuming no bandgap bowing), which is the largest energy of any of the non-nitrides.  Accounting for bandgap reduction necessary to prevent inter-valley carrier transfer, photon emission in the 2.1-2.3 eV range (540-590 nm) is possible using the Al1-xInxP approach.  Furthermore, an innovative approach toward growth of lattice-mismatched semiconductor alloys allows the fabrication of previously-impossible combinations of materials on readily-available substrates.

This approach allows for highly efficient luminescence from LEDs operating in these spectral regions without the traditional penalty of photocarrier losses due to inter-valley carrier transfer.  Moreover, these innovations provide additional benefits from minimal mismatch strain, thus significantly simplifying device growth and fabrication.  As a result, this approach allows the production of highly efficient LED devices operating near the peak of the “human eye spectral response" and providing efficient light emission in the region of the green/amber gap.

Benefits

NREL's innovative amber LED technology offers significant advantages over current LED techniques, such as:

  • Proven efficiency increases: Demonstrates twice the efficiency of current amber LEDs
  • Easy manufacturing: Can be fabricated simply on a large scale with existing MOCVD manufacturing equipment
  • Low-cost materials: Uses the same commercially available substrates as for current amber and red LEDs—gallium arsenide (GaAs)
  • Better white LEDs: Enables color-mixing white LED architectures that:
    • Emit more white light, with an estimated 20% increase in luminosity
    • Avoid Stokes-shift energy losses while minimizing photocarrier losses
    • Improved color with a color rendering index (CRI) greater than 95.
Applications and Industries

NREL's amber LED will have a major impact on the trend toward energy efficiency across multiple industries, including:

  • SSL
    • Conventional LED-based solid-state lamps
    • General lighting, backlighting, etc.
    • Industrial and residential lighting
    • Components for automotive, medical, consumer electronics, etc.
  • Photovoltaics (PVs)
  • Ultra-high efficiency solar PVs
  • Utility-scale and industrial solar PVs
  • Lasers
More Information

See additional publications:

Patents and Patent Applications
ID Number
Title and Abstract
Primary Lab
Date
Application 20120032187
Application
20120032187
Lattice-Mismatched GaInP LED Devices and Methods of Fabricating Same
A method (100) of fabricating an LED or the active regions of an LED and an LED (200). The method includes growing, depositing or otherwise providing a bottom cladding layer (208) of a selected semiconductor alloy with an adjusted bandgap provided by intentionally disordering the structure of the cladding layer (208). A first active layer (202) may be grown above the bottom cladding layer (208) wherein the first active layer (202) is fabricated of the same semiconductor alloy, with however, a partially ordered structure. The first active layer (202) will also be fabricated to include a selected n or p type doping. The method further includes growing a second active layer (204) above the first active layer (202) where the second active layer (204) Is fabricated from the same semiconductor alloy.
National Renewable Energy Laboratory 04/15/2010
Filed
Application 20130221326
Application
20130221326
High Bandgap III-V Alloys for High Efficiency Optoelectronics
High bandgap alloys for high efficiency optoelectronics are disclosed. An exemplary optoelectronic device may include a substrate, at least one Al.sub.1-xIn.sub.xP layer, and a step-grade buffer between the substrate and at least one Al.sub.1-xIn.sub.xP layer. The buffer may begin with a layer that is substantially lattice matched to GaAs, and may then incrementally increase the lattice constant in each sequential layer until a predetermined lattice constant of Al.sub.1-xIn.sub.xP is reached.
National Renewable Energy Laboratory 10/12/2011
Filed
Technology Status
Technology IDDevelopment StageAvailabilityPublishedLast Updated
NREL ROI 09-36, 10-64. US and International Patents filed.Prototype - A p-i-n diode structure device has been synthesized which, when forward biased, functions as an LED that emits amber light well within the green/amber gap (see image). Available - Please contact the NREL Commercialization and Technology Transfer Office for information concerning a license to use the technology, or a partnership to further develop it. 08/10/201007/28/2014

Contact NREL About This Technology

To: Bill Hadley<bill.hadley@nrel.gov>