Photoluminescence studies of ZnO thin films on porous silicon grown by plasma-assisted molecular beam epitaxy

ZnO thin films were grown on porous silicon (PS) by plasma-assisted molecular beam epitaxy (PA-MBE). The optical properties of the ZnO thin films grown on PS were studied using temperature-dependent photoluminescence (PL). At room temperature, the full width at half maximum (FWHM) of the near-band-edge emission (NBE) from the ZnO thin films was 98 meV, which was much smaller than that of ZnO thin films grown on a Si substrate. This value was even smaller than that of ZnO thin films grown on a sapphire substrate. The Huang–Rhys factor S associated with the FX emission from the ZnO thin films was found to be 0.124. The Eg(0) value obtained from the fitting was 3.37 eV, with α = 3.3 × 10−2 eV/K and β = 8.6 × 103 K. The activation energies of the low- and high-temperature region were 9 and 28 meV, respectively. The exciton radiative lifetime in the ZnO thin films showed a non-linear behavior, which was established using a quadratic equation.

► ZnO thin films were grown on buffer layers with different thicknesses.
► The films were also grown on both Si and porous silicon substrates.
►  The properties of the films were enhanced with increasing the thickness.
► By introducing PS as a substrate, the properties of the films were improved.