Enhancing AZO thin films for optoelectronics: the impact of substrate temperature and vacuum annealing

Abstract

Aluminum-doped zinc oxide (AZO) thin films, a promising candidate for advanced optoelectronic applications, were deposited using a direct-current (DC) magnetron sputtering system at various substrate temperatures. This study systematically investigates the impact of deposition temperature and post-deposition annealing on the structural, electrical, optical, and chemical properties of AZO thin films. Films deposited at mid-temperature (MT, 160 °C) exhibited superior electrical performance, including high carrier mobility (21.35 cm²/Vs) and low resistivity, compared to films deposited at low and high temperatures. Post-deposition annealing at 300 °C for 30 min under vacuum further enhanced the conductivity by significantly increasing the carrier concentration, as confirmed by photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS), which revealed the role of oxygen vacancies (V_O) and zinc-related defects (O_Zn) in the conduction band. To optimize light-trapping properties, AZO thin films were etched using 0.5% hydrochloric acid (HCl) for 35 s, achieving a haze ratio of 36% and a sheet resistance of 10 Ω/sq. These optimized films were integrated into a-Si:H/μc-Si:H tandem solar cells, resulting in a short-circuit current density (J_SC) of 13.66 mA/cm² and an efficiency (η) of 13.52%. These findings highlight the importance of controlling deposition and annealing conditions to optimize the performance of AZO thin films, paving the way for their integration into next-generation photovoltaic and optoelectronic devices.