Growth Activation of ZnO Layers with H2O Vapor on a-Face of Sapphire Substrate by Metalorganic Molecular-Beam Epitaxy

H2O vapor‐activated ZnO layers have been grown on the a‐face of sapphire substrates. The grown ZnO layers revealed a crystalline orientation of c‐face ZnO ‖ a‐face sapphire. For the II/VI flux ratio of 14, the ZnO layers showed a bandedge luminescence with the emission energy of 3.376 and 3.304 eV at 17 K and room temperature, respectively. The amount of the blue‐shifted energy in the Zn‐rich ZnO is estimated to be ∼30 meV in comparison to the donor‐bound exciton emission reported previously. The energy shifting towards the higher level could be attributed to the drastic reduction of carrier concentration in the order of ∼1017 cm—3 for the II/VI flux ratio of 14. With this growth condition, electron mobility is recorded typically to be ∼90 cm2/Vs which is considerably higher for the same carrier concentrations reported previously with plasma as oxygen source.