Considerable efforts are made today to reproducibly grow low-resistive ZnO films since this semiconductor is a very promising material for blue and ultraviolet light-emitting devices fabrication. Like many other wide-band-gap semiconductors, undoped ZnO has naturally n-type conduction, and it is difficult to invert its conduction type. Recently, a co-doping technique [1] were proposed to produce low-resistive p-type ZnO by simultaneous incorporation of group III (Ga, Al, In) and N elements. According to this technique group III metal and N elements are doped at the same time and creating N acceptor centers are stabilized by the formation of N-III-N (III = Ga, Al, In) type complexes. It was reported in [2] on preparation of p-type ZnO films by this way by pulsed laser deposition from Ga-doped ZnO target in N₂ atmosphere.

In our study, the ZnO:Ga films were implanted by N⁺ ions with 180 keV energy at various nitrogen concentrations. ZnO:Ga films were grown by chemical vapor deposition method. The Ga concentration determined by a secondary ion mass spectroscopy (SIMS) was 3*10¹⁸ cm^-3. Implanted nitrogen concentrations in samples were approximately 5*10¹⁷, 6.5*10¹⁸, and 1*10¹⁹ cm^-3. As a reference sample, Ga-undoped ZnO film were also N⁺-implanted with the same concentration. After implantation, the samples were high-temperature annealed in air at 950 ^oC for 2 hours to remove the formed radiation Frenkel-pair defects.

Four point van der Pauw and cathodoluminescense methods were used to measure the electrical and optical properties of the samples. ZnO:(Ga, N) samples with N concentrations 6.5*10¹⁸, and 1*10¹⁹ cm^-3, where there were sufficient number of N atoms to form N-Ga-N bonds, were found to be of p-type conduction with acceptor density 5*10¹⁶, and 3*10¹⁷ cm^-3; respectively. No conduction type inversion was observed in non-Ga-doped ZnO films. These results indicate that co-doping of ZnO with Ga and N is more effective than ZnO doping only with N. Besides, our studies show that the conduction type inversion can be also achieved by the N⁺ implantation of previously Ga-doped ZnO films. Although the acceptor density in the films is apparently low for many electronic applications, the proper optimization of growth parameters can sufficiently improve the electrical properties of p-ZnO films.