Photoluminescence, photoacoustic and Raman spectra of zinc oxide films grown by LP-MOCVD using diethylzinc and water as precursors

Polycrystalline zinc oxide (ZnO) films were grown on alkali-free glass substrates by low pressure metalorganic chemical vapor deposition (LP-MOCVD) using diethylzinc (DEZn) and water (H2O) as precursors. Photoluminescence (PL) spectra of the films were composed of the near-band-edge (NBE) emission at similar to 380 nm and the orange band (OB) emission at similar to 600 nm. Variations of the intensity ratio of the NBE emission to the OB emission (I-NBE/I-OB) and the photon energy of the knee on the photoacoustic spectrum (PA edge) as a function of substrate temperature (T-S) could be divided into two regions at the boundary temperature (T-B). Below T-B, the NBE emission exhibited the tail extending to the higher energy than the bandgap of ZnO and the I-NBE/I-OB value became smaller with increasing T-S. In addition, the PA edge shifted towards lower energies with increasing T-S. Concerning the Raman results, these tendencies seem to have some relations with the decrease in concentration of the secondary phase Zn(OH)(2) with increasing T-S. Above T-B, however, the I-NBE/I-OB became larger and the PA edge shifted towards higher energies with increasing T-S, which is probably due to the removal of defect levels related to the excess oxygen atoms. (C) 2010 Elsevier B.V. All rights reserved.