[1] Alivov Y I, Look D C et al Solid State Electron.
2004 48 2343

[2] Makino T, Chia C H et al 2000 Appl. Phys. Lett.
77 1632

[3] Look D C, Mater. Sci. Eng. B 2001 80 383

[4] Ozgur U, Alivov Y I et al J. Appl. Phys. 2005
98 041301

[5] Look D C, Claflin B, Alivov Y I and Park S J 2004
Phys. Status Solidi 10 2203

[6] Look D C and Claflin B 2004 Phys. Status Solidi
241 624

[7] Klingshirn C 2007 Chem. Phys. Chem. 8 782

[8] LV J G, YE Z Z et al 2002 Chin. Phys. Lett. 19
1494

[9] Vaithianathan V, Lee B T, Chang C H, Asokan K and Kim S S
2006 Appl. Phys. Lett. 88 112103

[10] Limpijumnong S, Smith M F and Zhang S B 2006 Appl.
Phys. Lett. 89 222113

[11] Yan Y, Al-Jassim M M and Wei S H 2006 Appl. Phys.
Lett. 89 181912

[12] Krtschil A, Dadgar A et al 2005 Appl. Phys. Lett.
87 262105

[13] Bian J M, Li X M, Gao X D, Yu W D and Chen L D 2004
Appl. Phys. Lett. 84 541

[14] Bian J M, Li X M, Zhang C Y, Chen L D and Yao Q 2004
Appl. Phys. Lett. 84 3783

[15] Bian J M, Li X M, Zhang C Y, Yu W D and Gao X D 2004
Appl. Phys. Lett. 85 4070

[16] Fujimura N, Nishihara T, Goto S, Xu J F and Ito T 1993
J. Crystal Growth 130 269