a nanorod stack structure comprising a first semiconductor layer, a multi-quantum well layer, a second semiconductor layer, and an electrode layer sequentially stacked in a vertical direction and emitting light from a side surface of the nanorod stack structure, the side surface facing a horizontal direction perpendicular to the vertical direction, wherein each of a side surface of the electrode layer and a side surface of the second semiconductor layer extends in the vertical direction, and the side surface of the electrode layer is in line with the side surface of the second semiconductor layer; and

a functional material layer configured to cover the side surface of the nanorod stack structure and to enhance the light emission through the side surface of the nanorod stack structure by increasing a total internal reflection angle of the nanorod stack structure,

wherein the functional material layer is in contact with the side surface of the electrode layer and has a refractive index between a refractive index of the nanorod stack structure and a refractive index of air, and comprises a plurality of material layers having a refractive index distribution in which a refractive index decreases as a distance from the side surface of the nanorod stack structure increases.