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Antireflective package for optoelectronics


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Hello you all!


A decade ago I suggested to mix a nano-powder of high index ceramic in plastic to produce thinner spectacle lens. If the powder is fine enough, the composite acts as a uniform material and doesn't diffuse light.


Now I read that at light-emitting diodes (LED), laser diodes, photodetectors, photovoltaic cells... the high index of the semiconductor is said to create parasitic reflections at the chip's surface. I'm not quite convinced this is still the case: maybe books and Internet pages describe the situation several decades ago.


Anyway, a solution would be to encapsulate the chip in a transparent plastic loaded with nano-powder of high-index ceramic. This can be cheaper than anti-reflective coatings made by semiconductor processes, and work over a larger bandwidth. It's easier than for spectacle lens, since many opto components accept some diffusion.


Plastics for opaque encapsulation of semiconductors are commonly filled with a ceramic like silica. This stabilizes the dimensions against curing, humidity, temperature, to avoid mechanical stress. Opto components could choose a better ceramic like TiO2, ZrO2, GaN, SiC... The ceramic's composition, and its concentration in the plastic, can vary along light's path to optimize performance or price. Mixing several particle sizes eases high filling ratios, like in concrete.


Well, just in case this isn't already done...

Marc Schaefer, aka Enthalpy

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