Structural, optical, and thermoelectric properties of the ZnO : Al films synthesized by atomic layer deposition

Aluminum-doped zinc oxide thin films have been grown by atomic layer deposition at a temperature of 200$^\circ$C. Using X-ray diffraction, it has been established that the ZnO:Al thin films exhibits the reflections from the (100), (002), (110), and (201) ZnO hexagonal phase planes. The (101) and (102) planes have also been detected by electron diffraction. The ZnO:Al thin films grow smooth with a root-mean-square roughness of $R_q$ = 0.33 nm and characteristic nanocrystallite sizes of $\sim$70 and $\sim$15 nm without additional aluminum or aluminum oxide phases. The transmission at a wavelength of 550 nm with regard to the substrate has been found to be 96%. The refractive indices and absorption coefficients of the ZnO:Al thin films in the wavelength range of 250–900 nm have been determined. The maximum refractive indices and absorption coefficients have been found to be 2.09 at a wavelength of 335 nm and 0.39 at a wavelength of 295 nm, respectively. The optical band gap is 3.56 eV. The resistivity, Seebeck coefficient, and power factor of the ZnO:Al thin films are $\sim$1.02 $\times$ 10$^{-3}$ $\Omega$ cm, –60 $\mu$V/K, and 340 $\mu$W m$^{-1}$ K$^{-2}$ at room temperature, respectively. The maximum power factor attains 620 $\mu$W m$^{-1}$ K$^{-2}$ at a temperature of 200$^\circ$C.