gold but can be other materials the fusing layer may be evaporated sputtered or otherwise attached to the second metal layer block 122 represents fusing the fusing layer on the first substrate and the fusing layer on the second substrate together the fusion is accomplished by placing the two fusing layers in close contact and then placing the two wafers in an oven at 300 degrees centigrade for four hours the temperature of the oven is ramped up at 1 degree centigrade per minute stays at 300 degrees for four hours and then is ramped back to room temperature at one degree centigrade per minute block 124 represents removing the second substrate from the fused assembly the second substrate is removed using wet or dry etch processes the removal of the second substrate can be aided by using a stop etch layer between the substrate and the epitaxial layer block 126 represents etching the n contact and n cladding layers the etch process may be more than one actual etch the etch process may also use the n contact layer as a mask to etch the n cladding layer there are masked regions of the wafer where the n contact layer and.