1. Department of Electrical Engineering, Shiraz University, P.O. Box: 71345‐1457, Shiraz, Iran
2. Institute for Material Research, Tohoku University, Sendai 980‐8577, Japan
3. Department of Electrical Engineering, Tarbiat Modares University, P.O. Box 14115‐143, Tehran, Iran
4. Semiconductor Group, Laser Research Center, AEOI, Tehran, Iran