Indium gallium nitride

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InGaN blue LED (380–405 nm)
Spectrum of a white-light LED where GaN or InGaN blue source pumps Ce:YAG phosphor

Indium gallium nitride (InGaN,

bandgap
can be tuned by varying the amount of indium in the alloy. InxGa1−xN has a direct bandgap span from the infrared (0.69 eV) for InN to the ultraviolet (3.4 eV) of GaN. The ratio of In/Ga is usually between 0.02/0.98 and 0.3/0.7.[1]

Applications

LEDs

Indium gallium nitride is the light-emitting layer in modern blue and green

solar photovoltaic devices, specifically for arrays for satellites
.

It is theoretically predicted that

segregation has been observed in experimental local structure studies.[2] Other experimental results using cathodoluminescence and photoluminescence excitation on low In-content InGaN multi-quantum wells have demonstrated that providing correct material parameters of the InGaN/GaN alloys, theoretical approaches for AlGaN/GaN systems also apply to InGaN nanostructures.[3]

GaN is a defect-rich material with typical dislocation densities

diode lasers.[6][7][8] The indium-rich regions have a lower bandgap than the surrounding material and create regions of reduced potential energy for charge carriers. Electron-hole pairs are trapped there and recombine with emission of light, instead of diffusing to crystal defects where the recombination is non-radiative. Also, self-consistent computer simulations have shown that radiative recombination is focused where regions are rich of indium.[9]

The emitted wavelength, dependent on the material's band gap, can be controlled by the GaN/InN ratio, from near ultraviolet for 0.02In/0.98Ga through 390 nm for 0.1In/0.9Ga, violet-blue 420 nm for 0.2In/0.8Ga, to blue 440 nm for 0.3In/0.7Ga, to red for higher ratios and also by the thickness of the InGaN layers which are typically in the range of 2–3

nm[citation needed]. However, atomistic simulations results have shown that emission energies have a minor dependence on small variations of device dimensions.[10] Studies based on device simulation have shown that it could be possible to increase InGaN/GaN LED efficiency using band gap engineering, especially for green LEDs.[11]

Photovoltaics

The ability to perform bandgap engineering with InGaN over a range that provides a good spectral match to sunlight, makes InGaN suitable for

solar photovoltaic cells.[12][13] It is possible to grow multiple layers with different bandgaps, as the material is relatively insensitive to defects introduced by a lattice mismatch between the layers. A two-layer multijunction cell with bandgaps of 1.1 eV and 1.7 eV can attain a theoretical 50% maximum efficiency, and by depositing multiple layers tuned to a wide range of bandgaps an efficiency up to 70% is theoretically expected.[14]

Significant photoresponse was obtained from experimental InGaN single-junction devices.[15][16] In addition to controlling the optical properties,[17] which results in band gap engineering, photovoltaic device performance can be improved by engineering the microstructure of the material to increase the optical path length and provide light trapping. Growing nanocolumns on the device can further result in resonant interaction with light,[18] and InGaN nanocolumns have been successfully deposited on SiO
2 using plasma enhanced evaporation.[19] Nanorod growth may also be advantageous in the reduction of treading dislocations which may act as charge traps reducing solar cell efficiency [20]

Metal-modulated epitaxy allows controlled atomic layer-by-layer growth of thin films with almost ideal characteristics enabled by strain relaxation at the first atomic layer. The crystal's lattice structures match up, resembling a perfect crystal, with corresponding luminosity. The crystal had indium content ranging from x ~ 0.22 to 0.67. Significant improvement in the crystalline quality and optical properties began at x ~ 0.6. Films were grown at ~400 °C to facilitate indium incorporation and with precursor modulation to enhance surface morphology and metal adlayer diffusion. These findings should contribute to the development of growth techniques for nitride semiconductors under high lattice misfit conditions.[21][22]

Quantum heterostructures

Quantum heterostructures are often built from GaN with InGaN active layers. InGaN can be combined with other materials, e.g. GaN, AlGaN, on SiC, sapphire and even silicon.

Nanorods

InGaN nanorod LEDs are three-dimensional structures with a larger emitting surface, better efficiency and greater light emission compared to planar LEDs [citation needed].

Safety and toxicity

The toxicology of InGaN has not been fully investigated. The dust is an irritant to skin, eyes and lungs. The

MOVPE sources have been reported recently in a review.[23]

See also

References

  1. doi:10.1002/anie.201105633
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  3. doi:10.1002/pssc.200460305.{{cite journal}}: CS1 maint: numeric names: authors list (link
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  5. ^ P. G. Eliseev. "Radiative processes in InGaN quantum wells". Archived from the original on 8 April 2013.
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  7. ^ HJ Chang; et alter. "Strong luminescence from strain relaxed InGaN/GaN nanotips for highly efficient light emitters" (PDF). Retrieved 20 September 2013.
  8. S2CID 97464128.{{cite journal}}: CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link
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  14. ^ A nearly perfect solar cell, part 2 Archived 17 September 2020 at the Wayback Machine. Lbl.gov. Retrieved on 2011-11-07.
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  19. S2CID 53506014
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  20. PMID 24785272
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  21. ^ "Controlled atomic-layer crystal growth is 'breakthrough' for solar-cell efficiency". KurzweilAI. Retrieved 31 October 2013.
  22. doi:10.1063/1.4822122
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  23. doi:10.1016/j.jcrysgro.2004.09.007
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