A light emitting diode includes: an electrically conductive permanent substrate having a reflective top surface; an epitaxial film disposed on the reflective top surface of the permanent substrate and having an upper surface and a roughened lower surface that is opposite to the upper surface, the roughened lower surface having a roughness with a height of not less than 300 nm and a plurality of peaks which are in ohmic contact with the reflective top surface; an optical adhesive filled in a gap between the lower surface and the reflective top surface and connecting the epitaxial film to the permanent substrate; and a top electrode disposed on the upper surface and in ohmic contact with the epitaxial film.