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October, 2001 EEEL Provides Data on Index of Refraction of AlGaN |
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The Optoelectronics Division of EEEL has recently determined the refractive indices of aluminum gallium nitride films versus composition and wavelength. AlxGa1-xN is the primary materials system used for semiconductor lasers and LEDs operating in the green through violet portion of the spectrum. Such devices are enabling dramatic advances in solid state lighting, high-density data storage, displays, xerography, and medicine. Knowing the refractive index is one of the keys to more efficient device design and manufacture.
Industrial and university collaborators provided samples grown on sapphire substrates using both hydride vapor phase epitaxy (HVPE) and metal-organic chemical vapor deposition (MOCVD). MSEL's Albert Davydov determined aluminum mole fractions for each specimen by x-ray analysis. Norman Sanford of EEEL developed a prism coupling technique and analysis software to characterize the index, birefringence, and dispersion over a wavelength range from 440 nm to 1060 nm. Thirteen compositions spanning the full composition range of interest were evaluated, and uncertainties as low as ± 0.003 in index were achieved.
The range of material composition examined, combined with the span of wavelengths covered and the full accounting for birefringence, makes this set of measurements the most comprehensive to date.
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