Polarization fields in (Zn,Cd)O/ZnO quantum well structures

The presence of polarization-induced electric fields of some 10(8) V/m in (Zn, Cd)O/ZnO quantum well structures is uncovered by a low-energy shift of the photoluminescence of several 100 meV as well as a dramatic increase of the lifetime from the sub-ns to the 100 mu s time scale when the well width increases from 1.2 to 5.4 nm. Effective screening of these fields by photogenerated carriers occurs already at moderate optical excitation in the 10 kW/cm(2) range.