Al-doping and Properties of AZO Thin Films Grown at Room Temperature: Sputtering Pressure Effect

Abstract

Aluminum zinc oxide (AZO) thin films were synthesized on glass substrates by radio frequency (rf) magnetron sputtering from a metallic Zn-Al (5 at. %) target at room temperature. The morphological, structural, electrical and optical properties of the films were studied as a function of the sputtering pressure, which was varied from 0.1 to 6.7 Pa. X-ray diffraction (XRD) analyses revealed that the films obtained were polycrystalline, having a hexagonal wurtzite structure with a preferential orientation in the (002) plane. In addition, the crystallite size increased as a function of sputtering pressure. Owing to the re-sputtering of the Zn atoms from the growing film, the aluminum concentration presented a maximum value of 13 at. %. At pressures close to 0.16 Pa, we obtained films with values of electrical resistivity and mobility of 2.8 10-3 Ω cm and 17 cm 2 /Vs, respectively. Finally, our results indicate that the structure zone diagram proposed by Thornton and later modified by Kluth does not fully predict the structural/morphological behavior of the AZO films, since plasma interactions must also be taken into account. With the methodology used, transparent conductive electrodes can be deposited on substrates at low temperatures.

Thickness-Dependent Growth Behaviors of Sputtered Amorphous InGaZnO Films Depending on the Substrates and Sputtering Conditions

“…Previous studies confirmed the existence of negative, positive, and neutral ions by analyzing particles during the oxide thin-film sputtering . Resputtering phenomena caused by negative ions, especially oxygen anions, were reported in various deposition processes. − Oxygen anions, with their high energies of hundreds of eV, can impact the substrate surface and remove the deposited material, causing resputtering . No oxygen gas was added during the sputtering up to this point in this work.…”

Preferential zinc sputtering during the growth of aluminum doped zinc oxide thin films by radio frequency magnetron sputtering

“…[33,34] Very recently it was demonstrated that gallium doped zinc oxide and ITO exhibit the same dependence of the selfbias with pressure as reported for AZO, however, only AZO exhibited the most noticeable correlation of the optoelectronic properties with the erosion track. [35] The optoelectronic and analytical properties of AZO thin films by sputtering have been intensively studied including X-ray photoelectron spectroscopy (XPS), [36][37][38][39] , X-ray diffraction (XRD) [36,[39][40][41][42] and Raman [37,40] for various parameters (pressure [43][44][45] , power [46][47][48] , target to substrate distance [32,49] , substrate material [50] , oxygen gas fraction [51,52] , substrate temperature [39] , plasma excitation mode [18,53,54] , annealing temperature, [55,56] target erosion [16] , Al doping fraction [57] ). However, so far, no conclusive correlation has been reported between the role of negative oxygen ions and the physical and chemical properties of AZO thin films as to be able to obtain resistivities below 10 -3 cm for a deposited area comparable with that of the target.…”

“…34 The optoelectronic and analytical properties of AZO thin films by sputtering have been intensively studied by X-ray photoelectron spectroscopy (XPS), 35–38 X-ray diffraction (XRD) 35,38–41 and Raman spectroscopy 36,39 for various parameters ( e.g. , pressure, 42–44 power, 45–47 target to substrate distance, 31,48 substrate material, 49 oxygen gas fraction, 50,51 substrate temperature, 38 plasma excitation mode, 18,52,53 annealing temperature, 54,55 target erosion, 16 and Al doping fraction 56 ). However, so far, no conclusive correlation has been reported between the role of negative oxygen ions and the physical and chemical properties of AZO thin films as to be able to obtain resistivities below 10 −3 Ω cm for a deposited area comparable with that of the target.…”

Selected properties of AlxZnyO thin films prepared by reactive pulsed magnetron sputtering using a two-element Zn/Al target

“…Moreover, in the literature regarding AZO thin films it can be found that the aluminium content can be as high as even ca. 20 atom % taking into account only Al and Zn [ 24 – 25 30 – 31 ].…”