Franz-Keldysh effect in epitaxial ZnO thin films

FERREYRA, J.M.; M. VILLAFUERTE; B. STRAUBE; G. NIEVA; J. GUIMPEL; C. A. FIGUEROA; G. BRIDOUX; S. P. HELUANI

Bariloche

Simposio; XXIII Latin American Symposium on Solid State Physics; 2018

Photoconductance spectroscopy has been studied in epitaxial ZnO thin films with different thicknesses that range between 136 and 21 nm. We report asystematic decrease of photoconductivity and a red shift of the band edge photoconductance spectra when the thickness is reduced. For thinner films, it isfound that the effective energy gap value diminish. By time dependent photoconductivity measurements we found a lower contribution of their slowercharacteristic relaxation times when thickness is diminished. These e_ects can be understood considering a band-bending contribution where the Franz-Keldysh effect and the polarization of the ZnO films play a major role for thinner films.