Microstructural, electrical and optical properties of ZnO:Mo thin films with various thickness by spray pyrolysis

Abstract

Transparent conductive Mo-doped ZnO (MZO) thin films with different thickness are prepared by spray pyrolysis method on glass substrates. The structural, surface morphological, electrical and optical properties of these films have been investigated as a function of the film thickness by a series of characterization techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), energy-dispersive X-ray (EDX) analysis, Hall effect measurements, UV–vis and luminescence spectroscopy. The structural analysis results show that the films are crystallized in the wurtzite phase type. The structural disorder decreases and the crystalline quality of the films is gradually improved up to an optimum thickness of 1865nm. The SEM–EDX and elemental mapping results show that Mo is incorporated and distributed uniformly in all the MZO films. Hall measurement results indicated that the electrical properties depend considerably on film thickness. The resistivity decreases from 1.04×101 to 5.24×10−3Ωcm with the increase of MZO film thickness from 632nm to 1865nm, and thereafter resistivity increases as thickness increases to 2290nm. UV–vis measurements show that the average transmittance of the MZO thin films is 71.2% and average surface reflectance is about 8.8% in the visible range. The optical band gap and Urbach energy of the MZO films are also significantly influenced by the film thickness. The photoluminescence (PL) measurements indicate that the intensity of deep level emission significantly vary with the film thickness.