A co-activating route was employed to fabricate ZnO light-emitting diode (LED) by using molecular beam epitaxy. N-2 was used as the acceptor dopant source and O-2 was used as assistant gas for N-2 decomposing more than only oxygen source. Emission spectra of the N-2 + O-2 mixture plasma were monitored in situ in order to adjust growth parameters timely. Under the assistance of O-2, N atoms content in the plasma of the mixture shows a significant increase compared to the case without O-2 assistance. Electrical measurements of the as-grown p-type ZnO on sapphire show a carrier concentration of 1.2 x 18 cm(-3) and a mobility approaching 1 cm(2)V(-1)s(-1). A ZnO LED was fabricated by depositing undoped n-type ZnO on the p-type layer. The turn-on voltage at 100 K is about 3.70 V, which approaches the bandgap of ZnO. Electroluminescence spectra show two bands: one is centered at 423 and the other centered at 523 nm, respectively. (c) 2006 Elsevier B.V. All rights reserved.