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 ~ 380 nm and the orange band (OB) emission at ~ 600 nm. Variations of the intensity ratio of the NBE emission to the OB emission (INBE/IOB) and the photon energy of the knee on the photoacoustic spectrum (PA edge) as a function of substrate temperature (TS) could be divided into two regions at the boundary temperature (TB). Below TB, the NBE emission exhibited the tail extending to the higher energy than the bandgap of ZnO and the INBE/IOB value became smaller with increasing TS. In addition, the PA edge shifted towards lower energies with increasing TS. 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 TS. Above TB, however, the INBE/IOB became larger and the PA edge shifted towards higher energies with increasing TS, which is probably due to the removal of defect levels related to the excess oxygen atoms.