Pulsed laser deposited stoichiometric ZnO thin films

Room temperature free-exciton emission was observed in stoichiometric ZnO epilayers grown on Al₂O₃ substrates by pulsed laser deposition. Absorption and photoluminescence measurements clearly showed the free-exciton emissions at 3.30~3.31 eV. This free-exciton recombination results from the high-quality single-crystalline ZnO epilayers. Temperature-dependent excitonic properties revealed the higher thermal stability of stoichiometric ZnO epilayers with the effective phonon energy, electron-phonon interaction and exciton-phonon coupling of 65.2 meV, 0.093 meV/K and 680 meV, respectively. The strong exciton-phonon coupling has been attributed to the high Frohlich constant due to the strong localization energy in the stoichiometric ZnO epilayers.