Remote plasma ALD of SrTiO3 using cyclopentadienlyl-based Ti and Sr precursors

Remote plasma atomic layer deposition (ALD) of SrTiO3 films with different [Sr]/[Ti] ratios is reported, employing Star-Ti [(pentamethylcyclopentadienyl)trimethoxy-titanium, (CpMe5)Ti(OMe)3] and Hyper-Sr [bis(trisisopropylcyclopentadienyl)-strontium with 1,2-dimethoxyethane adduct, Sr(iPr3Cp)2DME] precursors and O2 plasma. The as-deposited films were amorphous, but crystallized after post-deposition anneal above 500°C. For annealed SrTiO3 films with [Sr]/[Ti]=1.3 and a thickness of 50 nm, a high dielectric constant k>80 and low leakage current of ~10-7 A/cm2 at 1 V were obtained. It is demonstrated that changes in the composition and microstructure are apparent in the optical dielectric function of the SrTiO3 films, as obtained by spectroscopic ellipsometry

Probing charge carrier density in a layer of photodoped ZnO nanoparticles by spectroscopic ellipsometry

Changes in the optical constants of a layer of ZnO nanoparticles (5 nm diameter) induced by UV illumination in O2-free atmosphere are determined by using spectroscopic ellipsometry. The onset of optical absorption of ZnO shifts to higher photon energy after illumination. This is interpreted in terms of a Moss-Burstein shift. From the magnitude of the shift, the charge carrier density in the conduction band after UV illumination was determined to be 2 × 1019 cm-3, about one carrier per particle. Kelvin probe measurements give a lower limit for the density of 1018 cm-3. The free carrier density after illumination is high enough to explain the formation of quasi-ohmic contacts between ZnO and the polymeric p-type conductor poly(3,4-ethylenedioxythiophene) (PEDOT)