The Relevant Characteristics Of Aluminum Doped Zinc Oxide Films

In recent years,Al-doped zinc oxide(AZO) films has been a hot topic in transparent conductive film field not only because of their comparable optical and electrical properties to ITO films,but also because of their low cost,abundance in natural resource,and high stability in a hydrogen plasma environment.Surface textured AZO film,an alternative front contact material of SnO₂ in microcrystalline silicon film solar cells,has been paid much attention to.In this paper,AZO films were prepared on glass substrate by direct current pulse reactive magnetron sputtering(DCP-sputtering) and direct current reactive magnetron sputtering(DC-sputtering),respectively.The effect of deposition parameters on the structural,electrical,and optical properties of AZO films was investigated systematically by scanning electron microscopy(SEM),x-ray diffractometry(XRD), four point probe and UV-VIS-IR spectrophotometry,respectively.The optical constants of the as-deposited AZO films were fitted by envelop method(EM) and spectroscopic ellipsometry(SE),respectively.In addition,the as-deposited AZO films were textured by 5%NH₄Cl aqueous solution.And the texture process and texture mechanism were deeply investigated.The effect of DCP-sputtering and DC-sputtering was also comparably studied on the surface texture of the as-deposited AZO films by using NH₄Cl aqueous solution.The results indicate:(1) The as-deposited AZO films by DCP-sputtering technique lost a(002) c-axis preferential orientation,which might originate from the evolution of the crystal face energy and the transition of film grow mode.The resistivity decreased firstly and then slightly increased at substrate temperature increasing from 210℃to 290℃.The change tendency of the resistivity was explained from the viewpoint of substrate temperature,film grow mechanism,crystal structure,and film surface structure, respectively.The blue and red shifts of the optical absorption edge occurred at substrate temperature below and above 270℃,respectively.The blue and red shifts were explained by Burstein-Moss effect.(2) The as-deposited AZO films by DC-sputtering technique exhibited ZnO-(002) and (103) characteristic diffraction peaks.In particular,the AZO film deposited at a substrate temperature of 200℃exhibited a strongest(002) preferential orientation. The resistivity decreased to 2.93×10^-3Ω·cm when substrate temperature increased from 170℃to 200℃and then increased at substrate temperature over 200℃.(3) The average refractive of AZO films prepared by DCP-sputtering at different substrate temperatures nearly keep constant(n≈2) in the visible wavelength range.SE was used to determine the dielectric constants of AZO films prepared by DCsputtering technique at different substrate temperatures.The real and imaginary parts of dielectric constants of AZO films demonstrate a slight change in the visible light range,while show a sharp change near the optical absorption edge.And the average values ofε₁ andε₂ in the visible light range are 3.4 and 0.25,respectively.The shift of the absorption edge was observed correspondly with the substrate temperature increasing from 170℃to 210℃.(4) The NH₄Cl aqueous solution was able to easily control the surface texture of the as-deposited AZO films by DCP-spttering and obtain an effective surface texture.The reflectivity of the textured AZO films in the visible region drastically decreased from 12%to 7.86%and the resistivity slightly increased.While the as-deposited AZO films by DC-sputtering showed no apparent surface texture.The result was able to be accounted for by relative stress and film compactability.