1. Department of Communication Engineering, Okayama Prefectural University, 111 Kuboki, Soja-shi, Okayama-ken 719-1197, Japan
2. GlobalWafers Japan Co., Ltd., 30 Soya, Hadano, Kanagawa, 257-8566, Japan
3. Department of Solid State Sciences, Ghent University, Krijgslaan 281-S1, Ghent B-9000, Belgium