“…At first, a 150-nm-thick polycrystalline ZnO layer was prepared on SiO 2 (fused silica glass) substrates by metalorganic chemical vapor deposition (MOCVD) 18) or molecular beam epitaxy (MBE). 19,20) These techniques provide device-grade ZnO 18,19,[21][22][23][24][25][26][27][28] and thus ensure to minimize the interfering effects of ZnO quality, such as crystallinity or impurity incorporation. Deposition temperatures of MOCVD-and MBE-ZnO were 400 °C and room temperature, respectively.…”