Structural, electrical, and optical properties of atomic layer deposition Al-doped ZnO films

Al-doped ZnO (AZO) films of similar to 100 nm thickness with various Al doping were prepared at 150 degrees C by atomic layer deposition on quartz substrates. At low Al doping, the films were strongly textured along the [100] direction, while at higher Al doping the films remained amorphous. Atomic force microscopy results showed that Al-O cycles when inserted in a ZnO film, corresponding to a few atomic percent Al, could remarkably reduce the surface roughness of the films. Hall measurements revealed a maximum mobility of 17.7 cm(2)/V s. Film resistivity reached a minima of 4.4 X 10(-3) Omega cm whereas the carrier concentration reached a maxima of 1.7 X 10(20) cm(-3), at 3 at. % Al. The band gap of AZO films varied from 3.23 eV for undoped ZnO films to 3.73 eV for AZO films with 24.6 at. % Al. Optical transmittance over 80% was obtained in the visible region. The detrimental impact of increased Al resulting in decreased conductivity due to doping past 3.0 at. % is evident in the x-ray diffraction data, as an abrupt increase in the optical band gap and as a deviation from the Burstein-Moss effect. (C) 2010 American Institute of Physics. [doi:10.1063/1.3466987]