Comparison of ferromagnetism in n- and p-type magnetic semiconductor thin films of ZnCoO

Both n- and p-type diluted magnetic semiconductor ZnCoO are made by magnetron co-sputtering with, respectively, dopants of Al and dual dopants of Al and N. The two sputtering targets are compound ZnCoO with 5% weight of Co and pure metal Al. Sputtering gases for n- and p-type films are pure Ar and N2, respectively. These films are magnetic at room temperature and possess free electron- and hole-concentration of 5.34×1020 and 5.27×1013 cm−3. Only the n-type film exhibits anomalous Hall-effect signals. Magnetic properties of these two types of films are compared and discussed based on measurements of microstructure and magneto-transport properties.

Research highlights
► n-type ZnCoO:Al and p-type ZnCoO:(Al, N) films are made and are both ferromagnetic at room temperature.
► Signal of anomalous Hall-effect (AHE) is clearly observed only for n-type film but not for p-type film.
► Photoluminescence (PL) spectrum shows a peak attributed to shallow acceptor band of N.
► Ferromagnetic exchange coupling between magnetic ions in n-type film is through spin polarized free electrons.
► Ferromagnetism in p-type film is not attributed to the free hole-carriers mediation but to the overlap of BMP.