Light emitting diodes are commonly used in various kinds of daily life products and applications such as illuminations, signal indicators, displays, computers, etc. Light emitting diodes transform electricity into light through combination of electrons and holes. Since the light emitted from light emitting diodes is luminescence, light emitting diodes have many advantages such as energy saving, fast response, no idling time needed, long life time, etc. Moreover, light emitting diodes are small in volume, have good impact resistivity, and may be mass produced by semiconductor manufacturing processes, so it is easy to fabricate small-sized or array-type devices in demands.
In recent years, energy issues have grown worse and worse and the whole world has put great effort into energy saving and carbon reduction, so it is a goal for industries to promote light extraction efficiency of light emitting diodes. In a perfect light emitting diode, the light generated by combination of electrons and holes may completely radiate to an external environment, achieving a light extraction efficiency of 100%. However, in fact, the internal structure and materials of a light emitting diode may lead to various light propagation loss, thus light can't completely radiate to an external environment and light extraction efficiency is reduced.
In order to promote light extraction efficiency of a light emitting diode, industries have already developed patterned sapphire substrates (PSSs) for light emitting diodes. Such patterned sapphire substrates may scatter light and reduce total reflection within the substrates so as to increase possibility of light radiating to an external environment and promote light extraction efficiency of light emitting diodes. However, the conventional patterned sapphire substrates still can't provide sufficient light extraction efficiency for light emitting diodes. Therefore, a patterned substrate for light emitting diode to further improve light extraction efficiency for light emitting diode is extremely needed.