Franz-Keldysh effect in epitaxial ZnO thin films

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

San Carlos de Bariloche

Congreso; SLAFES; 2018

Instituto Balseiro

Photoconductance spectroscopy has been studied in epitaxial ZnO thin films with different thicknesses that range between 136 and 21 nm. We report a systematic decrease of photoconductivity and a red shift of the band edge photoconductance spectra when the thickness is reduced. For thinner films, it is found that the effective energy gap value diminish. By time dependent photoconductivity measurements we found a lower contribution of their slower characteristic relaxation times when thickness is diminished. These effects 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.