N doping using N2O and NO sources:: From the viewpoint of ZnO

A study of N doping using N2O and NO sources on ZnO, which may prove important for the N doping of oxide materials, was performed by investigating the doping processes of N atoms by each source together with the various properties for the grown N doped ZnO films. N2O was employed as the radio-frequency (rf) plasma source to produce radical N-2* species that could effectively incorporate N atoms above 10(20) cm(-3) into ZnO, which was similar to N doping using N-2 as the source. In contrast, it was found that the ZnO films doped with a N concentration above 10(20) cm(-3) were easily obtained using a gas flow of NO. The N concentration could be controlled systematically by the simultaneous gas flow of NO and O-2 sources. The basis of N doping using a NO source could be related to the free radical characteristic of NO molecular. This idea was proposed from the results that the N concentrations doped to ZnO using a gas flow of N2O and N-2, which have the characteristics of neutral and nonreactive molecules in air, were in the ranges from 10(18) to 10(19) cm(-3). Further, our investigations clarified that the structural, optical, and electrical properties for the N doped ZnO films were not quite dependent on the N-2, N2O and NO sources used as N dopants. This work proposes that NO is a promising source as a N dopant that can be employed without using a rf plasma source in the application of physical vapor deposition techniques that are indispensable for producing radical N-2* species through a rf plasma source to achieve the efficient incorporation of N atoms when N-2 and N2O sources are used as N dopants. (C) 2004 American Institute of Physics.