p-type conductive NiO_x: Cu thin films with high carrier mobility deposited by ion beam assisted deposition

Transparent conductive NiO thin films with 18 at% Cu dopant were fabricated by ion beam assisted deposition (IBAD). Their structural and optoelectronic properties were compared with undoped NiO films and NiO films doped with 12 at% Cu, and also compared with NiO:Cu (18 at%) films deposited by RF sputtering as reported in our previous work. The results show that the crystallinity of NiO thin films deposited through IBAD technology is much better than that of the films deposited by RF sputtering. Thanks to this reason, the highest carrier mobility above 45 cm²V⁻¹s⁻¹ for NiO:Cu (18 at%) film can be realized here. Meanwhile, the films’ resistivity remains an acceptable value, varying from 2.05 to 0.064 Ω cm with oxygen ion beam current changing from 0.2 to 0.8 A. This feature is imperative for p-type transparent conductive oxides (TCOs) applied in various domains. In addition, with oxygen ion beam current increase, the increase of the Ni³⁺/Ni²⁺ ratio leads to more Ni²⁺ vacancies be introduced into NiO films, which is beneficial to generate holes and improve carrier concentration. In this work, the optimal carrier mobility of NiO film doped with 18 at% Cu is obtained when the oxygen ion beam current is 0.2 A. Its carrier concentration and electrical resistivity are 7.26 ×10¹⁶ cm⁻³ and 2.05 Ω cm, respectively.