Nitride Semiconductor Light Emitting Element with Bragg and Anti-Reflection Layers

The patent introduces a reflective layer as an intermediary component between the electrode and the active layer. This reflective layer can be made of materials with high reflectance (such as metal films or dielectric mirrors) without requiring the electrode itself to have high reflectance. The intermediary reflective layer enables both high light extraction efficiency and proper electrical contact formation, as the electrode can be made of materials that form good ohmic contacts while the reflective layer handles the light reflection function.

The patent addresses the critical angle limitation by introducing photonic crystal structures that operate in the spatial frequency domain rather than relying solely on geometric optics. The photonic crystal periodic structure creates allowed and forbidden bands for light propagation, enabling light extraction at angles that would normally be below the critical angle. This dimensional change from geometric angle control to spatial frequency control overcomes the interface angle limitation.

The patent segments the substrate function into two separate components: the sapphire substrate provides thermal and chemical stability during growth, while a separate conductive layer (such as a diamond-like carbon layer or metal contact layer) provides electrical conductivity. This segmentation allows each layer to optimize its specific function without compromising the other, enabling the device to benefit from both the stability of sapphire and the conductivity of the conductive layer.