Pressure controlled tunable magnetic, electrical and optical properties of (Cu, Li)-codoped ZnO thin films

• Three conductivity regimes were seen for the films with varying the growth pressure.
• Red-shift in optical band gap (Eg) happened as the growth pressure increased.
• Magnetism of the Zn(Cu, Li)O films could be tuned by controlling growth conditions.
• Only the film with n-type conduction exhibited room temperature ferromagnetism.

Zn0.989Cu0.01Li0.001O thin films have been deposited on c-plane sapphire substrates by pulsed laser deposition (PLD). The films deposited at 500 °C and the oxygen pressures (PO2) ranging from 0.04 to 40 Pa were of good crystallinity with a (0002) preferential orientation. Three conductivity regimes were observed for the films with varying the PO2. The n-type film obtained at 0.04 Pa had a low resistivity of 1.95×10−2 Ω cm, Hall mobility of 14.8 cm2 V−1 s−1, and carrier concentration of 2.16×1019 cm−3. The p-type Zn0.989Cu0.01Li0.001O film could achieve when oxygen ambient reached as high as 40 Pa and with a hole concentration of 1.12×1018 cm−3. Films grown at PO2 between 0.4 and 4 Pa commonly exhibited insulating behavior. All the Zn0.989Cu0.01Li0.001O films had a high transmittance above 80% in visible regions and the red-shift in optical band gap (Eg) happened as the PO2 increased. Magnetic measurements showed that only the film fabricated at 0.04 Pa with n-type conduction exhibited room temperature ferromagnetism (RTFM) of 0.25μB/Cu while others obtained at higher PO2 were paramagnetic. Oxygen vacancies (VO) are speculated that would play a crucial role for the ferromagnetic behavior observed.