Effects of Thermal Annealing on the Structural, Electrical and Mechanical Properties of Al-Doped ZnO Thin Films Deposited by Radio-Frequency Magnetron Sputtering

The structural, electrical and nanomechanical properties of Al-doped ZnO (AZO) thin films are investigated by means of X-ray diffraction (XRD), atomic force microscopy (AFM), Hall measurement and nanoindentation techniques. AZO thin films grown on glass substrates by using radio-frequency magnetron sputtering were annealed at the temperatures ranging from 300 to 500 degrees C. XRD results indicated that the annealed AZO thin films are textured, having a preferential crystallographic orientation along the hexagonal wurtzite (002) axis. Both the grain size and surface roughness of the annealed AZO thin films exhibit an increasing trend with increasing the annealing temperature. The carrier concentration of the as-deposited AZO thin films is 7.42 x 10(19) cm(-3) and decrease to 5.20 x 10(17) cm(-3) for the 500 degrees C annealing AZO thin films. Furthermore, the hardness and Young's modulus of the annealed AZO thin films were measured by a Berkovich nanoindenter operated with the continuous contact stiffness measurements (CSM) option. Nanoindentation results reveal that the hardness increases from 7.1 +/- 0.3 GPa to 11.2 +/- 0.4 GPa for films annealed at 300 degrees C and 500 degrees C, respectively. On the other hand, Young's modulus for the former is 98.6 +/- 3.9 GPa as compared to a value of 122.4 +/- 5.2 GPa for the latter.