Ultrafast carrier dynamics and third order nonlinear optical properties of aluminum doped zinc oxide (AZO) thin films

• Published in: Optical materials 2017-04, Vol.66, p.580-588
• Main Authors: Htwe, Zin Maung, Zhang, Yun-Dong, Yao, Cheng-Bao, Li, Hui, Yuan, Ping
• Format: Article
• Language: English
• Subjects: Al doped ZnO; Nonlinear optics; Simultaneous RF/DC sputtering; Thin film; Ultrafast carrier dynamics
• ISSN: 0925-3467; 1873-1252
• DOI: 10.1016/j.optmat.2017.03.009

Aluminum doped zinc oxide (AZO) thin films were fabricated by simultaneous RF/DC magnetron sputtering technique on sapphire (Al2O3) substrate with different DC sputtering power 2, 6, 8 and 10 W respectively. The sputtered thin films were annealed at 350 °C in order to improve the crystal quality. AZO thin films are systematically analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV-VIS spectrometer for structural and optical properties. XRD patterns show that all sputtered thin films are well crystallized with hexagonal wurtzite structure. SEM images reveal the average crystallite sizes are increased after doping Al in ZnO which agreed with the calculated values from XRD. All thin films possess high optical transmittance in visible region and optical band gap values are relatively increased with Al concentration. The ultrafast transient absorption (TA) of AZO was analyzed by femtosecond pump-probe spectroscopy. The kinetic TA curves were fitted by tri-exponential decay function and obtained decay time constants are found to be in few picosecond and nanosecond range for ultrafast and slow processes respectively. Third order nonlinear optical absorption and refraction coefficients were investigated by using Z-scan technique. The observed nonlinear coefficients are enhanced with Al concentration in ZnO. [Display omitted] •Crystal quality of ZnO thin films is improved after doping Al in ZnO.•All thin films show high optical transmittance in visible region.•Ultrafast and fast decay processes are dominated in AZO.•Nonlinear optical coefficients are relatively enhanced with Al concentration.