Investigation of the thermal photocarrier interaction-recombination in ZnO nanostructures fabricated by the hydrothermal method

The characteristics of the photocarrier transfer process in ZnO nanostructures fabricated on silicon substrates by the hydrothermal method are studied using temperature-dependent photoluminescence (PL) measurements. The luminescence shows distinct features arising from the dynamics of the excited carriers which occur as a consequence of the different size distributions of the ZnO nanostructures. It is found that the temperature-dependent photoluminescence phenomena can be attributed to the carrier-thermalization processes that occur in the ZnO nanostructures. The photogenerated carrier redistribution leads to a blueshift in the emission energy of the radiative transitions in the ZnO nanostructures. The random configuration of the photogenerated carriers in the ZnO nanostructures can be qualitatively understood in terms of the transition enthalpy and the transition entropy in the photocarrier transfer process. The oxygen vacancy induced emission with the trapping of electrons and spontaneous fluctuations of ZnO nanostructures has an influence on the variation of the full width at half maximum (FWHM). The carrier thermal escape and retrapping anomalies affect the temperature-dependence of the photoluminescence phenomena. The activation energy is larger for ZnO nanostructures with larger size distributions and the carrier confinement is better. Thermally-related spectroscopy allowed observation of the photon-phonon interactions associated with ZnO nanostructures with different size distributions.