The thickness of the second adhesive layer is preferably selected to be in a range of from 3 nm to 100 nm. [0038] (n-Electrode) [0039] A metal such as Al, V, Sn, Rh, Ti, Cr, Nb, Ta, Mo, W or Hf or an alloy of two or more kinds of metals suitably selected from these metals can be used as the material of the n-electrode joined to the n-type semiconductor layer.