Ultrathin Al-doped transparent conducting zinc oxide films fabricated by pulsed laser deposition

Abstract

Al-doped transparent conducting zinc oxide (AZO) films, approximately 20–110 nm-thick, were deposited on glass substrates at substrate temperatures between 200 and 300 °C by pulsed laser deposition (PLD) using an ArF excimer laser ( λ = 193 nm). When fabricated at a substrate temperature of 260 °C, a 40-nm-thick AZO film showed a low resistivity of 2.61 × 10 − 4 Ω·cm, carrier concentration of 8.64 × 10 20 cm − 3 , and Hall mobility of 27.7 cm 2/V·s. Furthermore, for an ultrathin 20-nm-thick film, a resistivity of 3.91 × 10 − 4 Ω·cm, carrier concentration of 7.14 × 10 20 cm − 3 , and Hall mobility of 22.4 cm 2/V·s were obtained. X-ray diffraction (XRD) spectra, obtained by the θ–2 θ method, of the AZO films grown at a substrate temperature of 260 °C showed that the diffraction peak of the ZnO (0002) plane increased as the film thickness increased from 20 to 110 nm. The full-width-at-half-maximum (FWHM) values were 0.5500°, 0.3845°, and 0.2979° for film thicknesses of 20, 40, and 110 nm, respectively. For these films, the values of the average transmittance in visible light wavelengths (400–700 nm) were 95.1%, 94.2%, and 96.6%, respectively. Field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM) observations showed that even the 20-nm-thick films did not show island structures. In addition, exfoliated areas or vacant and void spaces were not observed for any of the films.