Magnetic and optical studies of hydrogenated Cu-doped ZnO film

Significantly enhanced ferromagnetism and strong green emission were observed for Cu-doped ZnO films undergoing a hydrogenation process. After H₂ treatment at 500 °C, the saturation magnetization of 2 at% Cu-doped ZnO film (50 nm) is significantly increased from ∼1.65 emu cm^‑3 (0.3 µ_B/Cu) to ∼11.7 emu cm^‑3 (1.5 µ_B/Cu). The areal magnetization of the hydrogenated Cudoped ZnO is dependent on the film thickness, thus suggesting that it is Cu dopants that play dominant roles rather than surface magnetism arising from OH attachment. Detailed XPS and Raman analysis demonstrated that H₂ treatment may introduce more Cu (Cu¹⁺-like) impurities and oxygen vacancies that coupled with each other, resulting in ferromagnetic ordering. Furthermore, strong green emission can be obtained in hydrogenated Cu-doped ZnO films. The green emission is unlikely related with Cu dopants, but H₂ treatment can generate a unique structure with porous morphology and coexistence of complex defects that favors the green emission. The "green defects" are not simple O vacancies or H-incorporation and are stable after annealing at 700 °C under O₂ atmosphere. The high room temperature ferromagnetism and strong green light emission of hydrogenated Cu-doped ZnO film pave a way to its novel applications in future spintronics and optoelectronic devices.