Moreover, when the window layer 510 is n-type, the schottky electrode 516 can be made of the material selected from the group consisting of Au, Zn, Be and other metal or alloy that can form the schottky contact surface 518 with the window layer 510; when the window layer 510 is p-type, the schottky electrode 516 can be made of the material selected from the group consisting of Au, Ge, Ni and other