Low temperature photoluminescence and infrared dielectric functions of pulsed laser deposited ZnO thin films on silicon

C-axis oriented ZnO thin films were grown on silicon (100) and (111) substrates by pulsed laser deposition. Low temperature photoluminescence spectra show besides the peaks of free excitons, of defect bound excitons, and of a donor-acceptor pair transition a new doublet at 3.328/3.332 eV. The doublet seems to originate from the columnar textured ZnO film structure. A corresponding structural dependence of the broadening parameter of the infrared dielectric functions was derived from spectroscopic ellipsometry in the spectral range from 380 to 1200 cm^{- 1}. The wave numbers of the E₁ transverse optical and A₁ longitudinal optical phonon modes of the ZnO films on silicon are determined to be 406 and 573 cm^{- 1}, respectively. These values are slightly smaller than those of single-crystalline ZnO thin films on sapphire.