Deep ultraviolet LED and method for manufacturing the same
Provided is a deep ultraviolet LED with a design wavelength λ, including a reflecting electrode layer, an ultra-thin metal layer, and a p-type contact layer that are arranged in this order from a side opposite to a substrate; and a hemispherical lens bonded to a rear surface of the substrate on a side of the p-type contact layer, the hemispherical lens being transparent to light with the wavelength λ. The refractive index of the hemispherical lens is greater than or equal to the average value of the refractive index of the substrate and the refractive index of air and is less than or equal to the refractive index of the substrate. The hemispherical lens has a radius that is greater than or equal to the radius of an inscribed circle of the substrate and is about equal to the radius of a circumscribed circle of the substrate.
1. A deep ultraviolet LED with a design wavelength λ (200 to 350 nm), comprising:
a reflecting electrode layer, a metal layer, a p-GaN contact layer, a p-AlGaN layer, an electron blocking layer, a barrier layer, a quantum well layer, a second barrier layer, a n-AlGaN layer, an AlN buffer layer, and a sapphire substrate that are arranged in this order; and
a photonic crystal periodic structure having a plurality of air holes provided in a range of a thickness direction including at least an interface between the p-GaN contact layer and the p-AlGaN layer such that the photonic crystal periodic structure does not extend beyond the p-AlGaN layer toward the substrate,
the photonic crystal periodic structure consists of air and the p-GaN contact layer and the p-AlGaN layer,
the photonic crystal periodic structure has a photonic band gap,
the photonic band gap is open for transverse electric polarized components,
the wavelength λ, a period a of the photonic crystal periodic structure, and an average refractive index n av of materials forming the photonic crystal periodic structure satisfy a Bragg condition of mλ/n av =2a,
the average refractive index nav is obtained by two materials of the air and the p-AlGaN layer, having different refractive indices, on a bottom face of the photonic crystal structure,
an order m of the Bragg condition is in a range of 2<m<5,
a depth h of the air holes is greater than or equal to ⅔ a length of the period a,
a rear surface of the sapphire substrate has bonded thereto a quartz hemispherical lens that is transparent to light with the wavelength λ and
a radius of the hemispherical lens is greater than or equal to a radius of a circumscribed circle of the substrate.