[1] Nakamura S, Mukai T and Senoh M 1994 Appl. Phys.
Lett. 64 1687

[2] Chang S J, Chen C H, Chang P C, Su Y K, Chen P C et al
2003 IEEE. Trans. Electron. Devices 50 2567

[3] Narukawa Y, Kawakami Y, Fujita S and Nakamura S 1999
Phys. Rev. B 59 283

[4] Damilano B, Grandjean N, Massies J, Siozade L and
Ley-maire J 2000 Appl. Phys. Lett. 77 1268

[5] Amano H, Kito M, Hiramatsu K and Akasaki I 1989 Jpn.
J. Appl. Phys. I$\!$I 28 L2112

[6] Nakamura S, Mukai T, Senoh M and Iwasa N 1992 Jpn. J.
Appl. Phys. I$\!$I 31 L139

[7] Xu B, Yu Q X and Wu Q H 2004 Acta Phys. Sin.
53 204 (in Chinese)

[8] Li Z H, Yu T J, Yang Z J, Feng Y C, Zhang G Y, Guo B P and
Niu H B 2005 Chin. Phys. 14 1009

[9] Liu N X, Wang H B, Liu J P, Niu N H, Han J and Shen G D
2006 Acta Phys. Sin. 55 1424 (in Chinese)

[10] Wierer J J, Steigerwald D A et al 2001 Appl. Phys.
Lett. 78 3379

[11] Myers S M and Wright A F 2001 J. Appl. Phys.
90 5612