Since their first discovery and subsequent improvements, LEDs have always suffered several drawbacks when compared to traditional incandescent light bulbs, namely efficiency loss at high power and lack of reliable efficient solution for some colors in the spectrum, green for instance being one of the less favorable colors for LEDs.
At low power ranges, conventional LEDs based on gallium nitride are quite efficient, but as the power load increases, the efficiency decreases at faster rates therefore making them unsuitable for applications where high illumination power is needed.
Moreover, this problem is particularly severe with green LEDs.
In order to understand why, it is necessary to understand how LEDs work: light in LEDs is generated by the recombination of electrons and holes in an anode-cathode structure that lead to the release of photons. The wavelength of the light emitted is determined by the energy gap between the electrons and the holes.
Green LEDs are not as efficient as blue and red LEDs and therefore they are not produced in the same way but they are currently manufactured by filtering the blue light through a phosphor layer that changes the light wavelength into green: a solution that works but it is not much efficient
Simulations done by the U.S. Department of Energy show that it may be possible to create nanostructures that may lead to LEDs with better efficiency, especially green LEDs, by using novel nanostructures such as nanowires.
Nanowires, for example, may be customized so to act as LEDs when reduced to dimensions of 1nm or lower as by changing the dimensions of the nanowire to as thin as one atom, a phenomenon known as quantum confinement takes place and the bandgap in the structure increases accordingly moving the emitted light wavelength from the infrared region to visible light.
Moreover, changing the structure of the nanowire, it may be possible to fine-tune the band gap in order to produce light at the desired wavelength: for example, increasing the bandgap for InN nanowires to 2.3eV may produce green light without any need of filter and therefore dramatically improving the efficiency of the LED.
By changing the structure it is therefore possible to create different structures with different bandgaps and therefore emitting light of different colors: red, indigo and violet.
All such structures would produce light directly, therefore becoming much more efficient than LEDs producing light through a filter usually made by an extra layer of material.
Another strong advantage of this approach would be the fact that nanowires would be produced by a single material and therefore not by superimposing two layers of different materials one on another: using this approach there would be no mismatch between the crystal structures of the two materials and therefore the overall efficiency of the LED would be improved.
Lattice mismatch is one of the leading causes producing degradation of light as the holes and electrons in the two structures are not spaced in the same way and therefore mismatches are created within the structure producing a sharp decrease in the production of light.
This problem would not occur in structures made by nanowires and therefore produced using only one material.
If you are interested in GaN LED technology, please visit our GaN LED technology service page.
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