Room Temperature Ferromagnetism and Fast Ultraviolet Photoresponse of Inkjet-Printed Mn-Doped ZnO Thin Films

We have synthesized Mn-doped ZnO thin films by inkjet printing using a two-step annealing process at 200°C for the decomposition of the organic compounds, and at various temperatures above 400°C to tailor room temperature ferromagnetism. Highly c axis oriented 80 to 400 nm thin films on (001) Si substrates are obtained with a magnetic moment as large as 2.1¿B/Mn²⁺. X-ray absorption and emission spectra measurements at the O K edge and the Mn L edge suggest strong p-d hybridization between the Mn²⁺ and O^2-. Furthermore, Mn L edge XAS indicates the emergence of Mn³⁺/Mn⁴⁺ mixed valence states for films annealed above 500°C that leads to suppression of ferromagnetic ordering. All of these films show large and fast ultraviolet (UV) photoresponse with the decay times of about 0.5 ms, suggesting the potential for designing multifunctional UV sensors.