ZnO thin film sample is grown on sapphire substrate by MOCVD. The optical properties of the sample are investigated by Raman scattering, optical reflection, photoluminescence and stimulated emission. ₁ ^-1 ₁ ^-1 ₁ ^-1 ₂ ^-1...[ Read more ]

ZnO thin film sample is grown on sapphire substrate by MOCVD. The optical properties of the sample are investigated by Raman scattering, optical reflection, photoluminescence and stimulated emission.

The Raman spectra of the thin film sample are similar to that of the bulk crystal. A₁(TO) 377 cm^-1, A₁(LO) 575 cm^-1, E₁(TO) 410 cm^-1, E₂ 106 and 437 cm^-1, and various multi-phonon processes are observed. The intensity of these lines indicates the good quality of the thin film lattice structure.

Optical reflectance is obtained from cryogenic temperature to room temperature with vertical and horizontal polarized incident light. Three excitons A, B and C are observed in their ground state and n=2 state. Kramers-Kronig relations are employed to transform the reflection spectra into absorption spectra.

Photoluminescence spectra are also acquired from cryogenic temperature to room temperature. The dependence of the exciton emission intensity and the temperature is investigated. The energy between exciton and LO phonon interaction deviates from the value in literature, which may imply new aspect of their interaction.

Stimulated emission is performed by using different pumping rate at room temperature only. Emissions due to exciton-exciton collision and electron-hole plasma are observed. The buffer layer between ZnO thin film and sapphire substrate costs a huge loss, which reduces the emission efficiency greatly.