total reflection at the interface between the semiconductor buffer layer 23 and the voids therefore the light is scattered by the depressions of the patterned substrate 21 a after the formation of the semiconductor buffer layer 23 a light emitting stack layer 24 and a transparent conductive layer 25 are sequentially formed thereon as shown in fig2 d in the preferred embodiment the light emitting stack layer 24 is made of gan based materials and comprises a first semiconductor layer 241 of first conductivity type an active layer 242 and a second semiconductor layer 243 of second conductivity type the first conductivity type is n type or p type whereas the second conductivity type is different from the first conductivity type the structure of the active layer 242 can be a double heterojunction dh structure or a multi quantum well mqw structure for achieving higher internal quantum efficiency the transparent conductive layer 25 comprises metal or metallic oxide which is selected from the group consisting of nickel gold indium tin oxide cadmium tin oxide antimony tin oxide indium zinc oxide zinc aluminum oxide and zinc tin oxide a portion of light emitting stack layer 24 is removed by the conventional lithography etching process so as to expose a portion of the first semiconductor layer 241 a first electrode 27 is formed on the exposed first semiconductor layer and a second electrode 28 is formed on the transparent conductive layer 25 in a preferred embodiment the method further comprises forming a reflecting layer 28 on the lower surface of the patterned substrate 21 a for enhancing the light extracted from the sidewall of the substrate the reflecting layer 28 comprises at least one material selected from the group consisting of sn al au pt.