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

Abstract

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 (H 2O) 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 ( 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.