N codoping induced ferromagnetism in ZnO:Co $(101¯)$ thin films

By first-principles density functional calculations with generalized gradient approximation ZnO:Co $(101¯0)$ thin films have been demonstrated not to exhibit a ferromagnetic behavior in the absence of any additional carrier doping. Virtual crystal approximation is employed to introduce controlled hole concentrations by N codoping in dilute concentrations of 1–5 at. %. The results show that N codoping can change the ground state from antiferromagnetic to ferromagnetic while maximum ferromagnetic state stability occurs for a N concentration of 2 at. % which is practically achievable. Density of states analyses confirm that the substitutional N in the ZnO:Co thin film provides shallow acceptor states. N codoping is suggested to be a promising technique to realize $p$-type dilute magnetic semiconducting thin films in the dominantly paramagnetic ZnO:Co $(101¯0)$ system.