[1] [1] J. K. Wade, L. J. Mawst, D. Botez, and J. A. Morris, Electron. Lett. 34, 1100 (1998).

[2] [2] F. Dittmar, B. Sumpf, J. Fricke, G. Erbert, and G. Trankle, IEEE Photon. Technol. Lett. 18, 601 (2006).

[3] [3] G. Fang, X. Ma, G. Wang, M. Tan, and Y. Lan, Chinese J. Lasers (in Chinese) 31, 649 (2004).

[4] [4] J. Li, J. Han, J. Deng, D. Zou, and G. Shen, Chinese J. Lasers (in Chinese) 33, 1159 (2006).

[5] [5] D. Botez, Appl. Phys. Lett. 74, 3102 (1999).

[6] [6] M. Buda, W. C. van der Vleuten, Gh. Iordache, G. A. Acket, T. G. van de Roer, C. M. van Es, B. H. van Roy, and E. Smalbrugge, IEEE Photon. Technol. Lett. 11, 161 (1999).

[7] [7] K. Shigihara, K. Kawasaki, Y. Yoshida, S. Yamamura, T. Yagi, and E. Omura, IEEE J. Quantum Electron. 38, 1081 (2002).

[8] [8] J. J. Lee, L. J. Mawst, and D. Botez, J. Cryst. Growth 249, 100 (2003).

[9] [9] L. Zhong, J. Wang, X. Feng, Y. Wang, C. Wang, L. Han, F. Chong, S. Liu, and X. Ma, Chinese J. Lasers (in Chinese) 34, 1037 (2007).

[10] [10] G. Xin, R. Qu, Z. Fang, and G. Chen, Laser Optoelectron. Prog. (in Chinese) 43, (2) 3 (2006).

[11] [11] L. Li, G. Liu, Z. Li, M. Li, X. Wang, H. Li, and C. Wan, Chin. Opt. Lett. 6, 268 (2008).