Zinc oxide is an II-VI compound semiconductor with a wide direct band gap of 3.37 eV at room temperature. Undoped ZnO is usually n-type, which is associated with native point defects and/or residual hydrogen. On the other hand, Mn doped p-type ZnO is predicted to be ferromagnetic with the Curie temperature reaching 300K [1].
ZnMnO layers were fabricated by thermal oxidation of nitrogen doped ZnMnTe films grown by MBE on GaAs and ZnTe substrates. In samples grown on GaAs, As is accumulated in the ZnO region as revealed by the SIMS analysis. Arsenic most probably, diffused from the GaAs substrate during the oxidation process. As a consequence samples were doped with both As and N acceptors. The Hall measurements demonstrated p-type conductivity with the high hole concentration. The XRD on ZnMnO samples present wurtzite polycrystalline character with metallic Te inclusion.
In photoluminescence spectrum from p-ZnMnO sample we observe an intensive peak located at 3.357eV, probably related to exciton bound to a neutral acceptor A0X or possible to an exciton bound to a neutral donor D0X is resolved.
Magnetooptical studies were performed in the Faraday configuration. PL peak dependence on the magnetic field shows an energy shift and a characteristic saturation. Magnetization measurements show a paramagnetic behavior and allow to evaluate the molar faction of Mn to be x=0.003, 0.0045 and 0.006. We fit the PL peak position vs. magnetic field using the Brillouin function and estimate the exchange constant No(α-β)=0.1eV. This extremely small value in II-VI DMS is discussed.
We acknowledge the support from the foundation for Polish Science through a Subsidy 8/2003. Part of the research was supported by the grant 1 P03B 084 30.
[1] T. Dietl, et al. Science, 287, 5455, pp. 1019-1022. (2000).