*Long Yang1,2, Lixia Zhao1,2, Huiwang Wu1,2, Yafei Liu3, Balaji Raghothamachar3, Michael Dudley3
(1. Hebei Key Lab. of New Semiconductor Materials(China), 2. Hebei Poshing Electronics Tech. Corp. Ltd.(China), 3. Stony Brook Univ.(United States of America))