Fig. 3 presents the AFM images of a 44 lm2 scanning area as a function of the substrate temperature. It is seen that the surface morphology varies significantly with increasing substrate temperature. As the substrate temperature increased, the surface of AZO thin films exhibited rougher surfaces and the grain size became larger. The root-mean-square (rms) roughness increased from 1.89 nm to 2.67nm with increasing the substrate temperature from 0 C to 400C. This result is consistent with the application requirements for LEDs for which the rms roughness must be under 3 nm [20]. In general, the increased grain size leads to decreasing the grain boundary, which hinders the movement of carrier, and improving the conductivity. In our case, the contrary results appeared, so that the grain size is not critical parameter in electrical properties. Also, the rougher surface provides more opportunity for surface adsorption on the surface, resulting in degradation of electrical properties in AZO thin film. Therefore, the change of surface adsorption on the surface is observed and discussed below