[1] Dongguk Univ, Quantum Funct Semicond Res Ctr, Seoul 100715, South Korea
[2] Dongguk Univ, Dept Phys, Seoul 100715, South Korea
[3] Hanyang Univ, Dept Elect & Comp Engn, Adv Semicond Res Ctr, Seoul 133791, South Korea
[4] Chungbuk Natl Univ, Dept Phys, Cheongju 361763, South Korea
[5] DongbuAnam Semicond, Nano Etch Grp, Eumseong 369852, South Korea