H2O-vapor-activated ZnO growth on a-face sapphire substrates by metalorganic molecular-beam epitaxy

ZnO layers have been grown on a-face sapphire substrates using H2O vapor and O-2 plasma as oxygen sources. The growth rate of HO-vapor-assisted growth of ZnO (v-ZnO) is similar to3 times higher than that of plasma-assisted growth of ZnO (p-ZnO) for the same DEZn flux. This report addresses the higher growth activation of ZnO layers with H2O vapor than with O-2 plasma at the same substrate temperature. A sharp and intense photoluminescence (PL) spectrum is observed in v-ZnO at the neutral donor-bound exciton energy of 3.368eV at 16K. The PL excitation spectrum measurement revealed A and B free exciton energies of 3.382 and 3.388eV, respectively. On the other hand, the p-ZnO showed the band-edge emission energy of 3.373eV but with a very weak PL intensity and broader half width, The PL intensity from v-ZnO was similar to10(4) times brighter than that of p-ZnO and the integrated PL intensity measured at room temperature was kept to similar to1/8 of that measured at 16 K.