A shallow acceptor complex in Al-doped ZnO using N+ ion beam irradiation

Abstract

The co-doping strategy has been widely employed to obtain p-type ZnO. However, Al-doped ZnO has not been achieved for p-type character so far. Here, we have investigated a non-radiative defect introduced by a 40 keV N+ ion beam irradiation for Al-doped ZnO (AZO) films. We find that the shallow acceptor complex of NO-H-VZn can be created by irradiation with the N+ beam and an unintentional dopant of H in AZO films, and thus may contribute to the p-type conductivity. The activation energy for the acceptor complex was revealed to be 26 to 38 meV by analyzing low-temperature electron spin resonance (ESR) spectra. The resolved hyperfine signals in ESR spectra evidence an N-related acceptor with 14N (I=1), giving the hyperfine coupling constant of 12.3 MHz. Further, theoretical calculation supports that the defect complex introduced in the AZO systems features the p-type character. As a result, we demonstrate for the first time that the acceptor-donor of N-H co-doping may cause AZO to p-type character. Our intriguing findings pave the way for achieving p-type AZO with a proper acceptor-to-donor ratio, since the acceptor complex depends on the N+ beam irradiation dose.