The photoluminescence and stimulated emission characteristics of two types of periodically polarity-inverted ZnO grating structures have been investigated in detail. Strong photoluminescence in the step regions is observed for all the samples. However, electron-hole plasma emission is observed only for one type of sample consisting of Zn-polar ZnO/CrN and O-polar ZnO/Cr2 O 3 layers. Moreover, strong stimulated emission occurs only in the Zn-polar layers. These optical phenomena have been discussed in terms of the diffusion of excitons and local crystal quality.