Intersubband transitions in ZnO multiple quantum wells

Intersubband transitions in ZnO∕MgZnO multiple quantum wells (MQWs) are investigated by a photocurrent spectroscopy. Photocurrent peaks are observed in the energy range from 300to400meV and shifted to higher energy by reducing the ZnO well thickness. Polarization-resolved photocurrent spectra show that these peaks are observed when the polarization of incident lights is TM mode, following the intersubband selection rule. Calculation indicates that the photocurrent peaks are the intersubband transition from the first to the third subband in ZnO∕MgZnO MQWs.