In this paper, zinc oxide (ZnO) thin films and Al-doped zinc oxide (AZO) films are prepared. The XRD results show that the addition of Al ions at the middle stage of AZO film (ms-AZO) preparation can increase the grain size and change the preferential growth orientation from (100) crystal plane to (002) crystal plane. The results of UV-VIS spectra show that the addition of Al ions at the ms-AZO preparation can greatly increase the absorption intensity in the visible light region, and the addition of Al ions at the early stage of AZO film (es-AZO) preparation can make the blue shift of the ultraviolet absorption edge. The patterns of I–V curves show that the addition of Al ions can increase the forward current of AZO/Si heterojunction, comparing to that of ZnO/Si heterojunction. Furthermore, the leakage current mechanism may dominate the carrier transport.