Eur. Phys. J. B (2013) 86: 194
https://doi.org/10.1140/epjb/e2013-30595-4

Regular Article

Wavelength modulated excitonic spectra of Cu₂O thin films sandwiched by MgO plates^*

¹ Graduate School of Science and Technology, Kumamoto University, 2-39-1, Kurokami Chuo-ku, 860-8555 Kumamoto, Japan
² Shockwave and Condensed Matter Research Center, Kumamoto University, 2-39-1, Kurokami Chuo-ku, 860-8555 Kumamoto, Japan

^a e-mail: ayuohs.5780@gmail.com

Received: 13 July 2012
Received in final form: 24 December 2012
Published online: 29 April 2013

Abstract

We have investigated stress effects on yellow exciton states in a Cu₂O thin film sandwiched by MgO plates by measuring wavelength modulated (WM) absorption spectra and their thermal variations. In the WM absorption spectra, dispersive spectral structures owing to 2P~4P states in the yellow excitons are clearly resolved in the thin film sample. A stress due to the lattice mismatch between Cu₂O and MgO provides a large red shift of the band gap in the green excitonic system. However, in the yellow excitonic transitions, it is found that a red-shift of the 2P excitonic state is much smaller than that in the green excitonic system. This result suggests that a shallow potential minimum for the yellow excitons is built up in the Cu₂O thin film sandwiched by MgO plates.