the present invention now will be described more fully hereinafter with reference to the accompanying drawings , in which embodiments of the invention are shown . it is understood that when an element such as a layer , region or substrate is referred to as being “ on ” another element , it can be directly on the other element or intervening elements may also be present . it is understood that if part of an element , such as a surface , is referred to as “ outer ”, it is near from the outside of the device than other parts of the element . furthermore , the term “ directly ” means that there are no intervening elements . referring to fig1 , a first substrate 11 is provided . the first substrate 11 may be one of sapphire , si , gaas , inp , sic , or other suitable materials . referring to fig2 , a lapping stop layer 12 is formed on or directly formed on the first substrate 11 . a hardness of the lapping stop layer 12 is larger than that of the first substrate 11 . the lapping stop layer 12 is preferred to transparent , whereby it is not needed to be removed in the following procedure . it is understood that the lapping stop layer 12 may also be opaque which should be removed in the following procedure to increase a light emitting efficiency of the light emitting diode . the lapping stop layer 12 may be one of diamond , diamond like carbon ( dlc ), sic , al 2 o 3 , quartz , si 3 n 4 , sio 2 , gan , aln , inn or other suitable materials , or a mixture of two or more of diamond , dlc , sic , al 2 o 3 , quartz , si 3 n 4 , sio 2 , gan , aln , inn . the lapping stop layer 12 may be formed on the first substrate 11 by a process of metal organic chemical vapor deposition ( mocvd ), plasma - enhanced chemical vapor deposition ( pecvd ), evaporating , sputtering , or other chemical or physical processes . the lapping stop layer 12 may be configured as dots , islands , plates or other suitable shapes . the lapping stop layer 12 is evenly distributed on a surface of the first substrate 11 . voids defined in the lapping stop layer 12 may be a path of circuit , and also a place for deposition of an epitaxial layer 13 ( fig3 ) with high quality . the lapping stop layer 12 is 0 . 7 - 2 μm thick , which is a benefit for growing the epitaxial layer 13 . as shown in fig3 , the epitaxial layer 13 is grown on the lapping stop layer 12 . the epitaxial layer 13 is a multi - layered structure composed of semiconductor compounds . the semiconductor compounds include semiconductors of group iii - v or group ii - vi , and a typical one is a gan - based semiconductor . referring to fig4 , a second substrate 14 is bonded to the epitaxial layer 13 . the second substrate 14 may be one of si , al , cu or other suitable conductive materials . bonding the second substrate 14 on the epitaxial layer 13 may be accomplished with metallic bonding , adhesion , electronic plating , chemical plating or spin - coating , etc . as shown in fig5 , the first substrate 11 is removed by grinding , lapping or polishing . since the lapping stop layer 12 is harder than the first substrate 11 , lapping speeds of the two are quite different , and the lapping can be stopped precisely as soon as the lapping tool touches the lapping stop layer 12 . thereby , the epitaxial layer 13 is avoided to be lapped away by the lapping tool . as shown in fig6 , the lapping stop layer 12 is still remained in the epitaxial layer 13 . an exposed bottom portion of the epitaxial layer 13 and an exposed bottom portion of the lapping stop layer 12 cooperatively form a compound surface 16 . when the lapping stop layer 12 is transparent , there is no need to remove the lapping stop layer 12 , and an electrode 15 can be directly formed on the compound surface 16 to form a vertical light emitting diode 10 . in addition , the present embodiment comprises roughening the compound surface 16 by wet or dry etching for increasing a light output efficiency of the light emitting diode 10 , as illustrated in fig7 . referring to fig8 , in an alternative embodiment , the lapping stop layer 12 can be removed by etching ( such as inductively coupled plasma etching ) to expose the epitaxial layer 13 . the electrode 15 can be plated on the epitaxial layer 13 . accordingly , an outer surface of the epitaxial layer 13 can also be roughened to increase the light output efficiency of the light emitting diode 10 . the method of the present disclosure utilizing the characteristic of the different lapping speeds between the first substrate 11 and the lapping stop layer 12 , to precisely control a lapping value and prevent from destroying the epitaxial layer 13 . the method of the present disclosure is more suitable for manufacturing larger wafer and may save time and cost . it is believed that the present embodiments and their advantages will be understood from the foregoing description , and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the disclosure or sacrificing all of its material advantages , the examples hereinbefore described merely being preferred or exemplary embodiments of the disclosure .