[1] Chen Q, Yang J W, Osinsky A, Gangopadhyay S, Lim B, Anwar
M Z, Khan M A, Kuksenkov D and Temkin H 1997 Appl. Phys. Lett.
70 2277

[2] Katz O, Garber V, Meyler B, Bahir G, and Salzman J 2001
Appl. Phys. Lett. 79 1417

[3] Carrano J C, Gruowski P A, Eiting S J, Dupuis R D and
Campbell J C 1997 Appl. Phys. Lett. 70 1992

[4] Carrano J C, Li T, Grudowski P A, Eiting C J, Dupuis R D
and Campbell J C 1998 J. Appl. Phys. 83 6148

[5] Zhang S K, Wang W B, Shtau I, Yun F, He L, Morkoc H, Zhou
X, Tamargo M and Alfano R R 2002 Appl. Phys. Lett. 81
4862

[6] Lee M L, Sheu J K, Lai W C, Su Y K, Chang S J, Kao C J,
Tun C J, Chen M G, Chang W H, Chi G C and Tsai J M 2003 J.
Appl. Phys. 94 1753

[7] Van Hove J M, Hickman R, Klaassen J J, Chow P P and Ruden
P P 1997 Appl. Phys. Lett. 70 2282

[8] Osinsky A, Gangopadhyay S, Gaska R, Williams B, Khan M A,
Kuksenkov D and Temkin H 1997 Appl. Phys. Lett. 71 2334

[9] Collins C J, Chowdhury U, Wong M M, Yang B, Beck A L,
Dupuis R D and Campbell J C 2002 Appl. Phys. Lett. 80
3754

[10] Monroy E, Calle F, Munoz E and Omnes F 1999 Appl.
Phys. Lett. 74 3401

[11] McClintock R, Mayes K, Yasan A, Shiell D, Kung P, and
Razeghi M 2005 Appl. Phys. Lett. 86 011117

[12] Sze S M 1981 Physics of Semiconductor Devices 2nd
edn (New York: Wiley)

[13] Zhang X, Kung P, Walker D, Biotrowski J, Rogalski A,
Sazier A and Razeghi M 1995 Appl. Phys. Lett. 67 2028

[14] The freeware program 'AMPS-1D' is supplied by the
Electronic Materials and Processing Research Laboratory of Penn
State University, USA.

[15] Li N, Zhao D G and Yang H 2004 Solid State Commun.
132 701

[16] Brown J D, Yu Zhonghai, Matthews J, Harney S, Boney J,
Schetzina J F, Benson J D, Dang K W, Terrill C, Nohava Thomas, Yang
Wei and Krishnankutty Subash 1999 MRS Internet J. Nitride
Semicond. Res. 4 9

[17] Sabuktagin S, Moon Y T, Dogan S, Baski A A, and Morkoc H
2006 IEEE Electron Device Lett. 67 211

[18] Katz O, Bahir G, and Salzman J 2004 Appl. Phys.
Lett. 84 4092