Atomic layer deposition (ALD) is a promising nanomaterial synthesis technique due to its excellent confomality over complicated nanostructure. We fabricated ALD semiconducting oxide/semiconductor core-shell nanowire array and characterized the device performances as a photodiode. Si nanowires array with about 100∼300 nm diameter were prepared using electroless etching technique. Nitrogen doped ALD ZnO was carried out using diethylzinc (DEZ) and diluted NH4OH various growth temperature. We measured responsivity and external quantum efficiency of the fabricated device as a function of wavelength of incident light and compared with thin film based photodiode. For NW array device, the photocurrent density and responsivity were significantly enhanced compared to thin film based device. Also, by combining self-assembly process, well ordered core-shell ZnO/Si nanowire arrays were prepared. The device performance made of ordered core-shell NW arrays was significantly enhanced. In addition, ZnO homojunction NW photodiode as well as ALD TiO2 outer shell NW photodiodes were fabricated and their device characterizations were compared to the planar type device.