Study of stable p-type conductivity in bismuth-doped ZnO films grown by pulsed-laser deposition J. W. Lee, N. G. Subramaniam, J. C. Lee, S. Kumar S and T. W. Kang EPL, 95 4 (2011) 47002 Published online: 15 July 2011 DOI: 10.1209/0295-5075/95/47002