[1] Service R F 1997 Science 276 895

[2] Cong G W, Wei H Y, Zhang P F, Peng W Q, Wu J J, Liu X L, Jiao C M,
Hu W G, Zhu Q S and Wang Z G 2005 Appl. Phys. Lett. 87
231903

[3] \"Ozg\"ur U, Alivov Y I, C Liu, Teke A, Reshchikov M A, Doian S,
Avrutin V, Cho S J and Morko\c c H 2005 J. Appl. Phys. 98
041301

[4] B\o rseth T Moe, Svensson B G and Kuznetsov A Yu 2006 Appl.
Phys. Lett. 89 262112

[5] Leiter F H, Alves H, Pfisterer D, Romanov N G, Hofmann D M and
Meyer B K 2003 Physica B 340--342 201

[6] Kang H S, Kang J S, Kim J W and Lee S Y 2004 J. Appl. Phys.
95 1246

[7] Vanheusden K, Seager C H, Warren W L, Tallant D R and Voigt J A
1995 Appl. Phys. Lett. 68 403

[8] Wu X L 2001 Appl. Phys. Lett. 78 2285

[9] Lin B X and Fu Z X 2001 Appl. Phys. Lett. 79 943

[10] Lin Y J and Tsai C L 2006 J. Appl. Phys. 99 093501

[11] Coleman V A, Bradby J E, and Jagadish C 2006 Appl. Phys.
Lett. 89 082102

[12] Jejurikar S M, Banpurkar A G., Limays A V, Date S K, Patil S I and
Adhi K P 2006 J. Appl. Phys. 99 014907

[13] Van de Walle C G 2001 Physica B 308-310 899

[14] Chen M, Wang X, Yu Y H, Pei Z L, Bai X D, Sun C, Huang R F and Wen
L S 2000 Appl. Surf. Sci. 158 134

[15] Islam M N, Ghosh T B, Chopra K L and Acharya H N 1996 Thin
Solid Films 280 20

[16] Yang X J, Miao X Y, Xu X L, Xu C M, Xu J and Liu H T 2005
Opt. Mater. 27 1602

[17] Wang Z G, Zu X T, Zhu S and Wang L M 2006 Physica E 35
199