Industrial Technologies
Building Energy Efficiency
Advanced Materials
High Bandgap Phosphide Approaches for LED Applications
A new approach to fabricating green LEDs
National Renewable Energy Laboratory
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Device under forward bias emitting in the green gap.
Room temperature electroluminescence spectra of the device under different forward bias.
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 CMYK (cyan-magenta-yellow-black) 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 green emission wavelength for a three-color mixing scheme is approximately 560 nm, which maximizes the CRI and relaxes the requirements for the red and blue emission as well. Alternatively, amber LED with emission centered around 590 nm, which would enable CMYK color mixing. NREL scientists have devised a set of innovations to allow the manufacture of green and amber LEDs with high quantum efficiencies to enable white light with flexible CRI characteristics.
DescriptionIn 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 green and 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. NREL scientists have also been approaching the green gap not from the lower limit (540 nm) but from the upper limit (590 nm) using GaInP grown on conventional GaAs substrates.
These innovations enable a novel approach for obtaining LEDs that emit in the green, yellow and red regions of the visible spectrum. 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 and amber gap.
BenefitsIncreased efficiency, increased luminescence, lower photocarrier losses
Applications and IndustriesLED lighting, solid state lighting, building energy efficiency
More InformationSee additional publications:Patents and Patent Applications
ID Number |
Title and Abstract | Primary Lab |
Date |
|---|---|---|---|
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 20110070495 |
METHOD OF FABRICATING ELECTRODES INCLUDING HIGH-CAPACITY, BINDER-FREE ANODES FOR LITHIUM-ION BATTERIES
An electrode (110) is provided that may be used in an electrochemical device (100) such as an energy storage/discharge device, e.g., a lithium-ion battery, or an electrochromic device, e.g., a smart window. Hydrothermal techniques and vacuum filtration methods were applied to fabricate the electrode (110). The electrode (110) includes an active portion (140) that is made up of electrochemically active nanoparticles, with one embodiment utilizing 3d-transition metal oxides to provide the electrochemical capacity of the electrode (110). The active material (140) may include other electrochemical materials, such as silicon, tin, lithium manganese oxide, and lithium iron phosphate. The electrode (110) also includes a matrix or net (170) of electrically conductive nanomaterial that acts to connect and/or bind the active nanoparticles (140) such that no binder material is required in the electrode (110), which allows more active materials (140) to be included to improve energy density and other desirable characteristics of the electrode. The matrix material (170) may take the form of carbon nanotubes, such as single-wall, double-wall, and/or multi-wall nanotubes, and be provided as about 2 to 30 percent weight of the electrode (110) with the rest being the active material (140). |
National Renewable Energy Laboratory | 09/23/2009
Filed |
| Technology ID | Development Stage | Availability | Published | Last Updated |
|---|---|---|---|---|
| NREL ROI 09-36 | Prototype - A p-i-n diode structure device has been synthesized which, when forward biased, functions as an LED that emits green light well within the green 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. | 08/10/2010 | 01/21/2013 |
