OPTICAL AND ELECTRICAL CHARACTERISTICS OF ALUMINUM-DOPED ZNO THIN-FILMS PREPARED BY SOLGEL TECHNIQUE

Pure and aluminum-doped ZnO thin films of high quality were prepared b y the solgel deposition method. ZnO thin films are formed by a three-s tep decomposition of the chemical complex (Zn(CH3COO)(2). 2H(2)O) to Z nO. The aluminum doping was achieved by the addition of AlCl3. 2H(2)O and Al(NO3)(3). 9H(2)O in the methanol solution of the chemical comple x at an atomic ratio of Al/Zn = 10(-3)-10(-2). The films are transpare nt (90% optical transmittance) in the near UV, VIS and near IR ranges. X-ray diffraction analysis indicates that the crystallites of both Zn O and ZnO : Al thin films are preferentially oriented along the c-axis , [0 0 2] direction of the hexagonal crystal structure. The electrical conductivity of ZnO thin films increases with film thickness, under s elected heat treatments and with aluminum doping. The dark conductivit y and photoconductivity values of the films are in the range 10-100 [O mega cm](-1), which are considered adequate for certain solar cell and electrochromic applications. Measurements of the activation energy sh ow that pure and aluminum doped ZnO thin films have generally one dono r level around 50 meV and another at 120 meV below the conduction band . These results are used to explain the high electrical conductivity o f the films. (C) 1998 Published by Elsevier Science B.V. All rights re served.